TRIAC Progress Report - KEK

TRIAC Progress Report
TRIAC collaboration
(Edited by S. C. Jeong)
KEK Progress Report 2011-1
June 2011
A/H
High Energy Accelerator Research Organization

© High Energy Accelerator Research Organization (KEK), 2011
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i
KEK Progress Report 2011-1
June 2011
A/H
TRIAC Progress Report
TRIAC collaboration
(Edited by S.C. Jeong)
High Energy Accelerator Research Organization

TRIAC collaboration
S. Arai 1 , Y. Arakaki 1 , Y. Fuchi 1 , Y. Hirayama 1 , N. Imai 1 , H. Ishiyama 1 ,
S.C. Jeong 1 , I. Katayama 1 , H. Kawakami 1 , H. Miyatake 1 , K. Niki 1 , T. Nomura 1 ,
M. Okada 1 , M. Oyaizu 1 , M.H. Tanaka 1 , E. Tojyo 1 , M. Tomizawa 1 , N. Yoshikawa 1 ,
Y.X. Watanabe 1 , S. Abe 2 , T. Asozu 2 , S. Hanashima 2 , K. Horie 2 , S. Ichikawa 2 ,
H. Ikezoe 2 , T. Ishii 2 , N. Ishizaki 2 , A. Iwamoto 2 , H. Kabumoto 2 , S. Kanda 2 ,
K. Kutsukake 2 , M. Matsuda 2 , S. Mitsuoka 2 , M. Nakamura 2 , T. Nakanoya 2 , I. Ohuchi 2 ,
A. Osa 2 , Y. Otokawa 2 , M. Sataka 2 , T.K. Sato 2 , S. Takeuchi 2 , H. Tayama 2 ,
Y. Tsukihashi 2 , and T. Yoshida 2
K. Matsuta 3* , J. Murata 4* , T. Fukuda 5* , W. Sato 6* , S. Takai 7* , T. Teranishi 8* ,
H. Sugai 2* , H. Makii 2* , M. Shibata 9* , and D. Nagae 2*
1 High Energy Accelerator Research Organization (KEK), Ibaraki 305-0801, Japan
2 Japan Atomic Energy Agency (JAEA), Ibaraki 319-1195, Japan
3 Research Center for Nuclear Physics, Osaka University, Osaka 565-0871, Japan
4 Graduate School of Science, Rikkyo University, Tokyo 171-8501, Japan
5
Graduate School of Engineering, Osaka Electro-communication University,
Osaka 572-8530, Japan
6
Graduate School of Natural science and Technology, Kanazawa University,
Ishikawa 920-1192, Japan
7
Graduate School of Engineering, Tottori University, Tottori 680-8550, Japan
8 Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan
9 Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
* Spokespersons of the experimental proposals, not involved in the development of the
TRIAC facilities. They are included as representatives of respective experiments since
all experiments were performed in the framework of the TRIAC collaboration.
ii

PREFACE
The Tokai Radioactive Ion Accelerator Complex (TRIAC) is a radioactive ion
beam (RIB) facility of Institute of Particle and Nuclear Studies (IPNS), High Energy
Accelerator Research Organization (KEK), being installed at the Tokai Research and
Development Center, Japan Atomic Energy Agency (JAEA). The TRIAC is, in Japan,
the only low-energy accelerator complex for re-accelerating short-lived radioactive
isotope beams, operating as User Facility since the November of 2005.
The main components of TRIAC were primarily constructed at Institute for
Nuclear Study (INS), University of Tokyo, from 1992 to 1995 as a prototype for the
Exotic nuclear (E-) Arena of Japanese Hadron Facility (former name of the J-PARC).
The prototype facility was closed in 1999 and started to be re-installed at the JAEA
tandem accelerator facility from 2001 under the collaboration between KEK and JAEA,
which is now called TRIAC. The project for TRIAC has started with following
considerations: (1) The RIBs with energies above Coulomb barrier can be available at
low construction cost, by utilizing two existing linear accelerators (linacs), namely the
KEK linacs (SCRFQ / IH) and the JAEA superconducting linac (SC-linac). (2) The
uranium target in a form of UCx is available for RIB production at the tandem facility.
Although the connection of the two linacs has not yet been realized, the TRIAC
can provide beams of Uranium Fission Fragments with the maximum energy of 1.1
MeV/nucleon produced by protons of 30 MeV and 1 µA (30 W in beam power,
actually deposited in the production target) from the JAEA Tandem Accelerator.
In the present TRIAC, considering current trends of world-wide RIB facilities, we
recognize critical limitations in views of the re-accelerated energy and intensity of
available RIBs. The possibility for upgrading the present TRIAC has been seriously
discussed so far. As a result of such discussions, the TRIAC was determined to be
closed at the end of 2010. Hereby, we summarize the scientific activities mainly
performed at the TRIAC during the period of the operation (2006-2010). This
documentation includes the activities for the development of the production and
acceleration of RIBs, and experimental results obtained by using the short-lived RIBs
of the TRIAC.
We would like to express our great thanks to all scientists participating in all the
scientific activities (TRIAC developments and experiments) performed at the TRIAC.
iii

Contents
1. Introduction -1
2. Developments of the beam generation and acceleration at the TRIAC
2-1. Overview of the TRIAC -2
2-2. Ion source and target development -3
2-3. Charge Breeder -10
2-4. Accelerator -20
2-5. Beam transport line -39
2-6. Control system -43
2-7. Detector development -44
3. Experiments at the TRIAC
3-1. Nuclear astrophysics -52
3-2. Nuclear and fundamental physics -64
3-3. Materials Science -79
3-4. Experiments with the ISOL beam -90
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1. Introduction
Following the successful re-acceleration of short-lived radioactive ion beams
(RIBs) from the isotope separator on-line (ISOL) in the early 1990s, many ISOL-based
RIB facilities have been constructed over the world, and now are operating for various
research fields such as in nuclear physics, nuclear astrophysics, and materials science.
The low-energy RIBs, energy variable and with a high purity and good energy
resolution, are very effective not only for the detailed spectroscopic studies on nuclear
structure using nuclear reactions but also for studies on the structural and dynamical
properties of the bulk of materials.
At the Tandem accelerator facility of JAEA-Tokai, an ISOL-based radioactive ion
beam facility, TRIAC-Tokai Radioactive Ion Accelerator Complex - is operational since
the November of 2005. In the facility, short-lived radioactive ions produced by proton
or heavy ion induced nuclear reactions, after being mass-separated by the JAEA-ISOL,
can be accelerated up to the energy necessary for experiments. The energy is variable in
the range from 0.14 to 1.09 MeV/nucleon, which is the energy region available at the
first stage of the complete version of the TRIAC.
The present energy range of RIBs available at the TRIAC is suitable for direct
measurements for light ion induced nuclear reaction rates involved in the
nucleosynthesis at the explosive stage of the stellar evolution of massive stars as well as
in the early universe. The low energy RIBs can be also incorporated by implantation
into materials of interest whose properties can be probed with an unprecedented
sensitivity by using various nuclear spectroscopy techniques.
Since the first public operation, 50 days per year, in maximum, has been allowed
for experiments, including 10-day operation for the development of the RIB generation
and the acceleration at the TRIAC. The experimental proposals were carefully reviewed,
once a year, by the program advisory committee (PAC).
In the following, we first introduce the scientific activities for the developments of
RIB at the TRIAC. The summary of the experiments performed so far will follow.
2. Developments of the beam generation and acceleration at the TRIAC
The developments have been concentrated for the production and acceleration of
heavy (medium-mass) neutron-rich radioactive ion beams with high efficiency. The
followings are included in this section; (1) the development of target / ion source of the
JAEA-ISOL for effective production and ionization of uranium fission fragments, (2)
the development for charge breeding the singly charged ions from the ISOL, (3) the
development of post-accelerators for CW operation, upgrading acceleration energy, and
1

eam bunching, (4) the development of beam transport line and remote control system,
and (5) the development of detectors for beam diagnostics and experiments .
2-1. Overview of the TRIAC
The layout of the facility is given in Fig. 2-1. The TRIAC is based on an isotope
separator on-line (ISOL) and the radioactive nuclei are produced via proton-induced
fission of 238 U or heavy-ion reactions with the primary beams from the JAEA tandem
accelerator, which is not shown in Fig. 2-1. The produced radioactive nuclei are singly
charged and mass-separated by the JAEA-ISOL. They are fed to the 18-GHz electron
cyclotron resonance ion-source for charge-breeding (KEKCB), where the singly
charged ions are converted to multi-charged ions. The charge-bred radioactive ions,
usually with a mass (A) to charge-state (q) ratio of around 7 (A/q ~ 7), are extracted
again and fed to the post accelerator for re-acceleration. The post accelerator consisting
of two linear accelerators (linacs), a split-coaxial radio-frequency quadrupole (SCRFQ)
linac and an interdigital-H (IH) linac, can accelerate the RIB to the energy necessary for
experiments. The acceleration of the RIBs charge-bred by an ECR ion source was the
first time over the world and the overall efficiency of transmission from ISOL to the
experimental hall is about 2%. The basic parameters of the TRIAC are summarized in
Table 2-1.
Fig. 2-1. Layout of the TRIAC
Several experiments have been successfully performed, especially by using the 8 Li
beam with the intensity of several 10 5 particles per second (pps). The TRIAC now
provides beams of uranium fission fragments with the maximum energy of 1.1
MeV/nucleon, which are routinely produced by protons of 34 MeV and around 1 µA
(with a beam power of about 30 W) from the JAEA Tandem Accelerator, though the
2

maximum available beam power for the production is 90 W.
The progress report on the RIB generation and acceleration at the TRIAC made so
far from the early stage of the construction is summarized in the following.
Table 2-1. Basic parameters of the TRIAC
Primary Beam (JAEA) Ion (energy / intensity) P (36 MeV / 3 µA)*
Production target
(JAEA)
ISOL (JAEA) Ion source
Mass resolution
Charge Breeder (KEK) Ion source
Frequency / power
Linac Complex (KEK) Injection energy
Output energy
(variable)
: SCRFQ linac Frequency
output energy
duty cycle
: IH linac Frequency
output energy
duty cycle
* maximum proton beam power
3
7 Li (68 MeV / 300 pnA)
19 F (78 MeV / 100 pnA), etc.
UCx, BN, Mo, etc.
FEBIAD, SI type
1200
ECRIS
18 GHz / 1 kW
2.1 keV/nucleon
0.14-1.09 MeV/nucleon
25.96 MHz
178.4 keV/nucleon (A/q ≤ 28)
100 % (A/q ≤ 16), 30 % (A/q =
28)
51.92 MHz
0.14-1.09 MeV/nucleon (A/q ≤ 9)
100 % (A/q ≤ 9)
2-2. Ion source and target development
The JAEA ISOL is used for producing singly charged radioactive ion beams for the
TRIAC. One of the characteristics of the TRIAC is the acceleration of neutron-rich
fission fragments of 238 U induced by low-energy protons. The proton beam of 34 MeV
with intensity of ~ 1 µA is provided from the JAEA tandem accelerator. Two types of
integrated target-ion sources were developed; a forced electron beam induced
arc-discharge (FEBIAD-B2) type [2-1] and a surface ionization (SI) type ion sources.

The FEBIAD-B2 ion source is utilized for ionization of gaseous and volatile elements,
while the SI ion source is used for ionization of alkali, alkaline earth and rare earth
elements. With both ion sources, 105 neutron-rich radioisotopes of 19 elements were
successfully ionized and mass-separated up to now. In the following, the performance
of the ion sources is summarized.
2-2-1. FEBIAD type ion source
The FEBIAD-B2 ion source is shown in Fig. 2-2 (a) and compared to the
FEBIAD-E source (Fig. 2-2 (b)) recently developed for higher operating temperature. A
target container containing about 1 g/cm 2 of 238 UCx is directly attached to the hot
discharge chamber of the source (‘anode with grid’ in the figure).
Fig. 2-2. FEBIAD type ion sources with target container shown without the ion source housing. (1)
Proton beam, (2) capsule cathode, (3) anode with grid, (4) anti-cathode, (5) gas-inlet for the
operating gas from calibrated leaks. FEBIAD-B2 (a) with operating temperature of 1600–1900 K
and FEBIAD-E (b) with operation temperature 2000–2300 K are compared [2-2].
The present configuration of the target container with a heater, in addition to the
heater for cathode (capsule cathode in Fig. 2-2) and the connection pipe ensures to
effectively transport the fission products into the discharge chamber from the uranium
target via diffusion-effusion process.
UCx target preparation: A graphite fiber was chosen as starting material for
synthesizing uranium carbide target for the integrated target–ion source system.
Graphite fibers (φ = 11 µm, GC-20, Tokai Carbon Co.) were filled in the target
4

container of ion source and uranyl nitrate ( nat UO2(NO3)2 / 3M HNO3) solution was
impregnated. After drying in air atmosphere for the formation of UO2(NO3)2-6H2O, the
nitrates were out-gassed and converted to oxides such as U3O8 at about 900 K for about
1.5 hours in argon atmosphere. Then the target container of the oxides is loaded in the
target-ion source system, where the oxides are converted into UCx by in-situ sintering at
about 1800 K for about a half day. The target container (9 mm in diameter and 11-mm
long in case of FEBIAD-B2) is heated by electron bombardment (EB-heating). The
electrons were generated from the filament of the target heater. The potential difference
between the filament and the target container is about 200 V. A certain variation of the
target temperature does not affect the discharge parameters since the target chamber is
equipotential with the anode. The electric power of about 120 W (160 V / 0.75 A) was
supplied for the anode, about 180 W (220 V / 0.8 A) for EB-heating the target container,
when operating at the temperature of 1850 ± 50 K and 1800 ± 50 K, respectively. The
temperatures at the anode and the target were measured with an optical pyrometer and
the corresponding input powers were calibrated with the temperatures. Along this way,
in-situ preparation of UCx target was performed and the typical thickness of the carbide
target corresponds to the thickness of 600-800 mg/cm 2 of nat U. The process for target
preparation is summarized in Fig. 2-3.
Fig. 2-3. Target processing and photograph of the target base material.
The target/ion source was operated at temperature of about 1800 K and at the
pressure approximately 2 x10 -4 Pa. During the operation, ionization efficiencies for
stable xenon and krypton isotopes were periodically checked by using calibrated leaks
of 2.3 x 10 -7 and 4.6 x10 -7 atm cm 3 /s, respectively. The separation yields and
efficiencies for typical uranium fission fragments were summarized in Table 2-2. The
separation efficiency for an isotope is defined as the ratio of the yield mass-separated to
the calculated yield of production.
Although high separation efficiency was observed in the FEBIAD-B2 type ion
source, short-lived isotopes with half-lives shorter than 0.5 s such as 130, 131 In were
5

failed to be mass-separated, which is possibly due to the decay loss caused by a long
release time from the bulk of target material [2-3]. To reduce such decay losses for
short-lived isotopes in the target-ion source system, the higher operating temperatures,
e.g. around 2300 K just as the case of SI ion sources in Table 2-2, are desirable.
Table 2-2. Separation yields and efficiencies for Kr, Rb, Sr, Ag, In, Sn, Xe, Cs and Ba
Surface ionization type ion source operated at 2400 K, while FEBIAD-B2 operated at 1800 K. For
comparison, the measured separation yield is transformed to that to be obtained with the uranium
target thickness of 1 g/cm 2 and the proton beam current of 1 µA.
For this reason, a FEBIAD-E type ion source, which can be operated at the temperature
of 2000 – 2300 K [2-2], has been newly developed. In this type, as shown in Fig.2-2 (b),
the target container is heated by electron bombardment from a couple of tungsten
filaments surrounding the target container. The target container has a volume of 0.56
cm 3 (φ = 6 mm, L = 20 mm), and is welded to a connection pipe so as to avoid leaks for
vaporized fission products. The length of the target container is twice longer than that of
B2 type, while the volume is smaller by 20%. The FEBIAD-E type integrated target–ion
source, which was newly fabricated and off-line tested, has been recently on-line tested.
In the on-line test, the release properties of the short-lived radioisotopes of 93 Kr (T1/2 =
1.286 s), 129 In (T1/2 = 0.61 s) and 141 Xe (T1/2 = 1.73 s) were investigated [2-4]. The
uranium target container with a reduced size in the FEBIAD-E type was heated by
electron bombardment from a couple of surrounding tungsten filaments, and
successfully operated at 2000 °C. Accordingly, the release time for gaseous and volatile
elements was shortened as compared to the previous system (i.e. FEBIAD-B2); 2.6 s for
Kr, 1.8 s for In, and 4.6 s for Xe. Using this ion source system, short-lived isotopes of
6

gaseous and volatile elements (e.g. with lifetimes shorter than 1 s) could be provided for
decay and in-beam spectroscopy with a reasonable intensity.
2-2-2. SI type ion source
For ionization of alkali, alkaline earth and rare earth elements, a surface ionization
type ion source was used and shown in Fig. 2-4. A target container of tantalum with a
thickness of 0.5 mm was directly attached to the ionizer. With this configuration, target
materials can be loaded inside the ion source, which would be very effective to reduce
the release time. The inner surface of ionizer was covered by 50 µm-thick rhenium foil,
and the target container was loaded by about 650 mg/cm 2 of UCx. The integrated
target-ion source is heated by electron bombardment, i.e. electrons emitted from
filaments at a potential of typically 450 V relative to the ionizer / target container. The
ion source operates continuously for over one week at a temperature of 2400 K (total
power input of about 850 W), and can be used repeatedly. With the ion source, the
intensities of the mass-separated alkali, alkaline earth isotopes produced by
proton-induced fission of uranium were measured and summarized in Table 2-2.
2-2-3. Separation yields of neutron-rich isotopes (uranium fission fragments)
Using the FEBIAD-B2 type and SI type ion sources, we have extracted and
mass-separated 105 isotopes of 19 elements as ion beams. Figure 2-5 shows the
intensities of those isotopes available at the focal plane of the ISOL. Those intensities
can be increased by a factor of around 10 with the maximum proton beam power (36
MeV, 3 µA) and the uranium target thickness of 2.6 g/cm 2 .
Fig. 2-4. Surface ionization type ion source (U-SIS) and its power supplying scheme for heating. (1)
Proton beam, (2) thin foil, (3) uranium target, (4) target container (anode), (5) ionizer (the inner
surface is covered by a thin Re foil), (6) filament-1, (7) filament-2, (8) heat shields.
7

Fig. 2-5. Measured RIB intensities at the JAEA-ISOL. For some elements, more detailed
comparison is given.
Fig. 2-6. Separation efficiencies for Ba isotopes as a function of their half-lives. The solid line is
fitted by ε = ε0exp(τsln(2)/T1/2), where T1/2 is the decay half-life, τs is release time and ε0 is the
separation efficiency of 142 Ba. The dotted line is fitted to the data of 142,143,147 Ba. The real
characteristic time (release time) should be between 3 and 9.3 s, since the observed dispersion is
considered to be due to the experimental uncertainties.
2-2-4. Half-life dependence of separation efficiency
Release times and separation efficiencies for radioactive Kr, Rb, Sr, In, Xe, Cs, Ba
and Eu isotopes produced by the proton-induced fission of 238 UCx target were observed
to be strongly dependent on their life-times [2-3], which is shown for Ba isotopes as a
typical example in Fig. 2-6. For example, while the separation efficiency for 142 Ba (T1/2
8

= 10.6 m) were 4.5 %, that for 146 Ba (T1/2 = 2.2 s) was reduced to 0.4 %, i.e. by one
order of magnitude. Considering the decay loss, a characteristic time was extracted from
the correlation between separation efficiencies for isotopes and their half life-times as
shown in Fig. 2-6. The characteristic time for Ba was about 9 s, in good agreement with
release time measured for Ba in the present UCx target module. The release times were
considered to be governed mostly by diffusion process in the bulk of the present
uranium target; the diffusion speed from the uranium target used in this study changes
in the following order, i.e. Rb ~ Cs > Ba > Eu, showing the element dependence as
observed for release time.
Fig. 2-7. Release profile of 7 2-2-5. Production of
Li in the
graphite and BN target
8,9 Li
For producing 8 Li (T1/2 = 838ms), we have used a neutron transfer reaction of 13 C
( 7 Li, 8 Li), using a sintered target of 99%-enriched 13 C. The enriched 13 C graphite disk
(diameter of ~10mm, ≤1mm thick) was mounted to the catcher position of the SI type
ion source with a beam window of 3-µm thick
tungsten [2-1]. The target was bombarded with a
67-MeV 7 Li 3+ beam with intensity of about 100
pnA. In this condition, the separation yield of 8 Li
was evaluated to be 10 6 pps at the focal plane of
the JAEA-ISOL. However, the separation yield
of 9 Li (T1/2= 178ms) was observed as few as 10 2
pps.
A release profile of Li from the target ion
source system was measured using the heavy ion
implantation technique. As shown Fig. 2-7, the
fast component of release time (τ) for Li ions from the 13 C sintered target was 3.2 s.
Decay losses (defined as what remained on the release after decays) of 8 Li and 9 Li were
calculated by exp(-ln(2)/T1/2 x τ) where T1/2 is their half-life and τ is the release time,
giving 7.1x10 -2 for 8 Li and 3.9x10 -6 for 9 Li. Therefore, we could conclude that the
significantly reduced yield of 9 Li is caused by the rather long release time; most 9 Li
decayed out in the extraction processes (i.e. diffusion, effusion in the target materials)
when the graphite target was used.
In search for high-temperature-resistant target material for the production of 9 Li,
we found that boron nitride (BN) has shorter release time for Li; as shown in Fig. 2-7,
the fast component in the release profile from the 0.25mm-thick hot pressed BN sheet
was 120 ms. The decay losses calculated by above function were improved to 9.1x10 -1
9

for 8 Li and 6.3x10 -1 for 9 Li. With a hot pressed BN sheet target, we obtained the beam
of 9 Li with an intensity of 10 4 pps after separation by the JAEA-ISOL.
We observed that the release time became faster with decreasing thickness of the
BN sheet; the value of τfast was 1.9 s for 0.6-mm-thick BN, and 120 ms for
0.25-mm-thick BN. If the enhancement of the yield of 9 Li depends only on the fast
release time, we should also observe any thickness dependence in the ratio of yields
between 9 Li and 8 Li. However, the yield ratio of 9 Li / 8 Li was almost 1/10, irrespective
of the thickness of the BN sheet. In order to understand the observation, further
investigation would be necessary. Nevertheless, using the thick BN target, 9 Li of 3x10 4
pps (one order of magnitude less than the yields of 8 Li) at the target position of the
TRIAC were successfully supplied for experiments.
2-3. Charge breeder: KEKCB
The KEKCB is an electron cyclotron resonance (ECR) ion source operating at the
microwave frequency of 18 GHz, and has been operated for converting singly charged
radioactive ions from the JAEA-ISOL to highly charged ions with A/q < 7 for further
acceleration at the TRIAC.
2-3-1. Specification
The cross sectional view of the KEKCB is shown in Fig. 2-8. Some of the
important components are discussed as follows.
Energetic electrons, high plasma density and a good ionic confinement are
important ingredients for high charge breeding efficiency, leading to the effective
production of highly charged ions. For producing ions with A/q = 7, for example,
considerable fraction of electrons should have energies exceeding about 600 eV.
Creating this kind of hot electrons with high density in a minimum-B structure is not
difficult whenever a magnetic field configuration for the efficient confinement of hot
electrons and a high microwave frequency are employed. Following the recent scaling
law concerning the magnetic field configuration [2-5], we determined the axial and
radial magnetic mirror ratios possible with conventional solenoid coils and permanent
magnets; Raxial = 2.3 and Rradial = 1.7, where BECR = 0.64 T for 18 GHz. The mirror
ratios are very close to the optimum for an ECRIS operating with this frequency.
Ionic confinement time is closely related to the volume of the plasma chamber of
the source; the ions can reside in plasma for a long time, so that the ionic confinement
time becomes longer and accordingly highly charged ions can be created. With the help
of the systematic data which compare the charge state distributions of Ar from sources
10

with different plasma volumes [2-6], a plasma chamber around 1 l appears to be enough
for our purpose. Furthermore, the volume determined in this way can accommodate a
hot ECR zone with an axial length of 100 mm and a radial diameter of 50 mm. It would
be sufficiently large so that the ECR plasma could efficiently capture injected ions for
charge breeding.
The deceleration system in Fig. 2-8 is a simplified version of that used in the pilot
breeder [2-7]. Instead of the multi-step deceleration, two-step deceleration is adopted by
using two concentric cylindrical electrodes. The outer cylinder, 40 mm in diameter, is
operated as a final stage of deceleration, whereas the inner cylinder, 20 mm in diameter,
stays on the ground potential. Therefore, the main deceleration happens between two
electrodes and further smooth potential drop exists between the outer cylinder and the
plasma chamber. Both of the electrodes are altogether movable axially around the
position of the maximum axial magnetic field for the optimization of the injection under
the influence of the field. The outer cylinder is now removed because of the aging
problem of the insulator on which the electrode was attached. Instead, a similar shape of
electrode is directly attached to the inner tube (plasma chamber). The aging effect was
found due to the irradiation effect of RF wave unintentionally leaking from the ECR
chamber. In the present system, only the ground electrode (i.e. inner cylinder) is
movable and the outer electrode is always on the same potential as the plasma chamber.
Fig. 2-8. Cross-sectional view and specifications of the 18-GHz KEKCB
11

2-3-2. Charge breeding efficiency
The charge breeding efficiency εCB was found to depend strongly on the properties
of the beam injection and the ECR plasma [2-8]. In this section, we present two
conditions for optimizing the charge breeding efficiency and the resultant εCB. Two
stable beams of 129 Xe 1+ and 138 Ba 1+ were employed as pilot beams to search for the
optimum conditions. The beams were provided by the JAEA-ISOL; as previously
described in the section 2-2, the FEBIAD type ion source was used for gaseous and
volatile elements such as Xe ions, while the SI type ion source for alkali and alkaline
earth elements such as Ba ions.
Beam injection: We installed two collimators for defining the beam axis when
injecting singly charged ions to the KEKCB. One collimator functions as the entrance
hole for injection and the other as the exit hole for beam extraction of the KEKCB; their
diameters were 6 and 7 mm, respectively. The distance between them was about 300
mm. An additional collimator (the third one) with a diameter of 6 mm was used to
define the object point of the Einzel lens doublet placed upstream of the KEKCB as
shown Fig. 2-8. The third collimator was located 1000 mm upstream from the entrance
hole. At the first stage of beam tuning, we transported the stable beams from the
JAEA-ISOL to the exit of the KEKCB by using the collimator system without
deceleration, where the injection axis of beam optics could be defined. The typical
transport efficiency was around 60 %. We then began charge breeding by decelerating
the beam at the entrance. The beam injection was optimized by using the Einzel lens
doublet and electric quadrupole triplet located just upstream of the Einzel lens in the
beam transport line at the TRIAC. Tuning the injection was found to be very critical,
especially for charge breeding non-gaseous elements. The deceleration of the incident
beams was further optimized by adjusting ∆V, where ∆V denotes the electric potential
for adjusting the beam energy at injection into the ECR plasma. Figure 2-9 shows the
dependence of charge breeding efficiencies (εCB) for the 129 Xe 1+ and 138 Ba 1+ beams on
∆V. For Ba ions, a strong dependence was observed with a narrow width of about 4 V,
in contrast to the weaker dependence observed for Xe ions. The element dependence of
∆V is discussed below in detail. The results demonstrate that gaseous elements could be
more energetic at injection for higher εCB. For charge breeding RIBs whose masses
differed from that of the pilot stable beam, we only varied the parameters of the
analyzing magnet of the JAEA-ISOL since the other optical components in the beam
transport line are electric elements.
12

ECR plasma: We used natural helium as the support gas and a microwave power of
about 200 W to generate ECR plasma suitable for charge breeding. When we employed
oxygen gas, a lower microwave power of 150 W was sufficient to obtain the same εCB.
However, we adopted helium gas to avoid the long tail of the 16 O 2+ ions in the A/q < 8
region. The plasma that we used was optimized for the charge states of A/q ~ 7. The
charge state distributions for 129 Xe 1+ and 138 Ba 1+ are shown in Fig. 2-10, which show
that the highest values for εCB were obtained at A/q ~ 7. Both distributions were found
to have almost the same widths. The entrance hole for injection was found to play an
important role in reducing the microwave power loss and stabilizing the plasma. Before
installing the hole, a power as large as 400 W was required to achieve the same εCB for
the charge states of A/q ~ 7. The small hole is very effective not only to reduce the
conductance, but also to greatly reduce the microwave power loss, enabling us to
produce good plasma even with a low microwave power. The low power resulted in a
small amount of the total beam intensity being extracted, giving rise to a plasma stable
against the electrical discharge of the high voltage supply for beam extraction.
Fig. 2-9. ∆V versus charge breeding efficiency (εCB) for 129 Xe 1+ 129 Xe 19+ (dashed, but scaled down
by a factor of 3) and 138 Ba 1+ 138 Ba 20+ (solid). The charge breeding efficiency was defined by εCB =
(Iq+/q)/I1+ x100 (%), Iq+ and I1+ are the electric currents of charge-bred ions with a charge state of q+
and injected singly charged ions, respectively. ∆V is the electric potential difference between the 1 +
ion generator (SI for 138 Ba 1+ and FEBIAD for 129 Xe 1+ ) and the charge breeder. With increasing
values of ∆V, the 1 + ions become more energetic at the entrance of the ECR plasma. For indium
(metallic ions generated by FEBIAD as for Xe), the ∆V distribution was centered around 30 V in the
middle of the upward slope of εCB values for Xe with a width as narrow as for Ba (not shown here).
13

Fig. 2-10. Charge sate distributions of 129 Xe (lower panel) and 138 Ba (upper panel). Indices next to
the peaks indicate the charge states.
Table 2-3. Charge breeding efficiencies. Upper two rows indicate the gaseous elements, while the
lower rows present the non-gaseous elements. See the text for details.
Charge breeding efficiencies: The εCB for radioactive ion beams, 92 Kr 1+ and 126 In 1+ , as
well as the stable ion beams are summarized in Table 2-3 [2-8]. The efficiencies for
gaseous elements are higher by a factor of 3 than those for nongaseous elements. The
14

higher efficiency for gaseous elements is considered partly due to desorption of the
injected ions on the surface of the plasma chamber. The desorption of the gaseous ions
may lead to the weak dependence of εCB on the ∆V over a rather wider range as shown
in Fig. 2-8. On the other hand, the lower value of εCB for the nongaseous elements
suggests that the adsorption to the surface is not negligible. The improvement of the
beam injection efficiency to the ECR plasma may help increase εCB for the nongaseous
elements, if the ionization efficiency of ECRIS is element independent. The εCB was
found to be independent of the lifetime for radioactive nuclei with lifetimes of a few
seconds, as shown in Table 2-3. This result suggests that the charge breeding time is
shorter than the lifetimes of presently studied isotopes, which is consistent with the
charge breeding time of about 100 ms measured at the KEKCB [2-9]. We suppose that
εCB could be dependent on lifetime for RIBs with lifetimes shorter than a few 100 ms.
2-3-3. Element-dependent charge breeding efficiency
The charge breeding efficiencies are 7.4 % for Xe 20+ and 2.3 % for In 16+ , which are
typical efficiencies for radioactive gaseous and metallic elements with a half-life time of
~ 1 s., as well as for stable ions already shown in Fig. 2-8. The efficiencies for gaseous
elements are observed to be higher than those for metallic ones, usually by a factor of
three as long as the similar masses of the elements are concerned. Because of the
significantly different behavior in the injection, which just depends on if the element is
volatile or not at room temperature as discussed above, one can conclude that the lower
charge breeding efficiencies for metallic ions could be improved by more careful
optimization of the injection. The difference could be attributed to ad- and de-sorption
of the ions on the surface of the plasma chamber during the injection; the gaseous
elements adsorbed on the surface could be more easily desorbed and recycled for further
ionization, as compared to the case of metallic, non-volatile elements that stick to the
surface once adsorbed. On the other hand, the element-dependent ionization efficiency
cannot be completely excluded. Therefore, in order to identify the direction of the
development to obtain higher breeding efficiency, especially for metallic elements, it is
of importance to study how the injected ions, but failed to be re-extracted, are
distributed on the surface of the plasma chamber. The distribution of the injected ions
accumulated on the surface of the plasma chamber would help us to understand when
the injected ions are adsorbed, i.e. at the time of injection or in the course of the
step-by-step ionization in the ECR plasma after being well captured.
We have injected radioactive ions of 111 In into the KEKCB and, after charge
breeding, measured the residual activity to investigate how ions externally injected
15

should be lost in the course of charge breeding [2-10]. A typical azimuthal distribution
around the Bmin is given in Fig. 2-11. We assumed that the distribution consisted of three
components, azimuthally isotropic, 120 o -symmetric and asymmetric ones. At each
longitudinal (axial) position, we decomposed the distribution according to the azimuthal
symmetry; asymmetric and symmetric components. The symmetric includes isotropic
and 120 o -symmetric components. Integrating over azimuthal angle, the longitudinal
distributions were extracted and compared in Fig. 2-12, where axial magnetic field
configuration is also given. The asymmetric component is localized around Bmin, while
the symmetric component is concentrated around the Bmin as well as at the extraction
side.
Fig. 2-11. Azimuthal distribution of 111
In around Bmin. Decomposed into 3 components; azimuthally
isotropic, 120 o -symmetric, asymmetric ones.
Fig. 2-12. Longitudinal (axial) distribution of the symmetric and asymmetric components. The
injection and extraction positions are indicated by arrows, respectively. The symmetric includes both
the isotropic and 120 o -symmetric components. Axial magnetic filed configuration is also given by a
dotted line for comparison.
16

The asymmetric component representing 13.5 % of the total activity residual on the
surface might be associated with ions injected in a rather asymmetric manner, since the
(axial and radial) magnetic field configuration for the confinement of electrons in ECR
plasma cannot produce such asymmetry. More careful optimization of the beam optics
for the injection is necessary for the elimination of the asymmetric component in the
ion-losses in the course of charge breeding.
The 120 o -symmetric distribution of ions reminds us of the electron losses due to
the combined field configuration of the axial and the radial magnetic field for electron
confinement [2-10]. Although the behavior of ions in ECR plasma has not yet been
studied in detail both experimentally and theoretically, we can expect that both electrons
and ions should show a quite similar behavior. Therefore, the 120 o -symmetric
distribution can be considered as a characteristic behavior of ions in ECR plasma. When
considering the charge-breeding process as two successive processes, i.e. stopping and
ionizing processes [2-11], the ions with the 120 o azimuthal symmetry would correspond
to those lost during the second, ionizing process. In the ionization process, those ions,
though successfully captured by ECR plasma in the stopping process, are supposed to
be lost to the wall of plasma container along the hexagonal radial magnetic field. The
fraction, i.e. how many ions are lost in the ionization process, is nothing but the
ionization efficiency for the ions in ECRIS.
As shown in Fig. 2-11, the 120 o -symmetric component is on the top of the isotropic
one. The isotropic one is actually the main component of the symmetric distribution.
The isotropic component was observed all over the wall, while the 120 o -symmetric
component was observed only around Bmin, even where the isotropic component
amounts to a large fraction (refer to Fig. 2-11). Along the discussion given above for the
120 o symmetry in the distribution, the isotropic component could be also associated
with the incomplete confinement of ions, i.e. the losses simply by the ambipolar
diffusion of plasma constituents.
The symmetric component, which includes isotropic and 120 o -asymmetric
components, represents 86.5 % of the total. The 38 % of the symmetric component were
observed at the extraction side. The large fraction of ion losses around the extraction
side could be understood qualitatively by a weak confinement field. The weak radial
field caused by the geometrical limit of permanent magnets at the extraction side, as
well as the weak axial field for efficient ion extraction, could lead to rather poor radial
confinement of electrons and consequently large loss of ions along the radial direction.
Further measurements using the gaseous element 140 Xe have been performed. The
17

distribution of the residual activities of 140 Xe was compared with those of 111 In as shown
in Fig. 2-13. We observed well-localized azimuthal distribution with 120 o periodicity for
both elements, especially prominent around the minimum (Bmin at Z~200 mm) of the
axial field configuration for electron confinement. However, for the 111 In, an
asymmetric distribution with a strongly localized around φ~300 o and Z~200mm was
observed around the Bmin, while the 140 Xe distribution had almost same peak heights
(symmetric). In order to indentify the origin of the asymmetric components, further
experimental investigation is in progress.
Fig. 2-13. Distributions of residual activities of 111 In (left) and 140 Xe (right) on the surface of
plasma chamber as function of azimuthal angle (φ) and longitudinal position (z). See the text for
detail.
Analysis of the residual activity distribution on the ECR plasma chamber surface
revealed that most ions, especially gaseous 140 Xe ions, were lost on the side wall near
the central region where there is a minimum in the axial magnetic field for electron
confinement in the ECR plasma. While the 120° azimuthal periodicity is superimposed
on the isotropic distribution around Bmin, the lost ion patterns are almost azimuthally
isotropic on the extraction and injection sides. The azimuthal periodicity in the ion loss
pattern, which was observed for both volatile and non-volatile elements, differs from the
60° azimuthal periodicity around Bmin expected on the basis of the pattern of lost
electrons, which is often observed as an imprinted pattern on the inner surface of ECR
plasma chambers. The ion loss pattern, which was first observed by our present study,
18

ut differs from the electron-loss pattern, could be due to the direct injection of 1 + ions
for charge breeding; the injected ions may be preferentially stopped and captured on the
extraction side as a result of ion-plasma collisions
Additionally, a strong azimuthal asymmetric component localized near the central
region and a symmetric component localized on the extraction side, were observed in
the wall-loss distribution of the metallic 111 In ions. They account for 13.5 and 38.5 % of
the total side-wall loss of 111 In, respectively. They were not observed for xenon.
Therefore, the presence of such components in the wall-loss pattern of indium could be
why non-volatile metallic elements have lower charge breeding efficiency than gaseous
elements. We suggested that the charge breeding efficiencies for metallic ions at the
KEKCB could be improved by further optimization of the injection conditions for
charge breeding. However, it is not straightforward to further optimize our present
injection system than we have already performed for charge breeding non-volatile
metallic ions. Actually, the injection conditions can be varied by the parameters related
to the conditions of ECR plasma, which are not usually controllable in injection.
Therefore, more experimental works are required in order to identify the origin of the
loss patterns of metallic ions during the injection for charge breeding. Detailed
theoretical simulations are also highly desirable for gaining better understanding of the
present observations.
2-3-4. Beam impurities from KEKCB
The ECR plasma inherently produces a variety of ions from residual gases, the
plasma chamber, and other sources. Such ions are considered as impurities for the beam
of interest. To evaluate the impurity quantitatively, we accelerated background ions up
to 178 keV / nucleon by using the post-accelerator at the TRIAC [2-8]. As an example,
the background ions of A/q = 7.68 were selected by using an analyzing magnet and slits
with a full width of 10 mm along the horizontal direction (covering both sides of the
central trajectory) located at exit of the magnet. The magnet had a resolving power of
about 100 when the slits were open to 2-mm width. It is possible to identify the mass
number of impurity ions by measuring the total energy of the beams, since the
acceleration of the impurities has the same energy per nucleon. In the first trial, we
observed various heavy elements with an intensity of 10 7 ~ 10 8 pps. After this test, all
the materials exposed to the ECR plasma were converted to aluminum, since some of
them were made of stainless steal and chromium. Before installation, we ground their
surface using a sand blaster and high-pressure purified water, and cleaned them by
ultrasonic cleaning in order to remove any elements that had attached to their surfaces in
19

the machining processes. As a result, several peaks corresponding transition metallic
elements disappeared, and the intensity of the impurity peaks decreased dramatically to
about 600 pps in total, making it feasible to perform experiments with the RIBs. The
main component of the remaining impurities is considered to be krypton, which is
naturally abundant in the residual gases in the source. When the beam was defined more
rigorously by the slits, from 10 to 2 mm in width, a reduction of more than a factor of 5
was expected for the background. In reality, however, the actual desired beam reduction
was a factor of 2. We also checked the region of A/q between 6 and 7. As an example,
we studied the background ions of A/q = 6.45, which is very close to 6.4 ( 32 S 5+ ) and 6.5
( 13 C 2+ ), with the slits of 2 mm in width. The background intensity was found to be only
several tens of pps.
It should be noted that the intensity of background components measured at the
focal plane of the analyzing magnet of the KEKCB was about 1 nA, not depending on
the surface-cleaning: Most of them can be removed at the TRIAC, not only by
additional beam optics fine-tuned to A/q of 6.45 in the beam transport line but also
during acceleration.
2-4. Accelerator
The post accelerator at the TRIAC comprises a 25.96-MHz split-coaxial RFQ with
modulated vanes and a 51.92-MHz interdigital–H (IH) linac, as shown in Fig. 2-1. Main
specifications of the RFQ / IH linac are listed in Table 2-4.
2-4-1. Specification: SCRFQ / IH linacs
SCRFQ linac: The SCRFQ accelerates ions with a charge-to-mass ratio (q/A) greater
than 1/28 from 2 to 178 keV/nucleon. The duty factor can be 30 % for ions with q/A =
1/28 and 100 % for q/A > 1/16. The cavity, 0.9 m in inner diameter and 8.6 m in length,
comprises four unit cavities, each of which is composed of three modules. Obtained
flatness of the longitudinal field distribution is within ±1 %. Unloaded Q-value is 5800.
The resonance resistance (= V 2 /2P) is 24.55 ± 0.44 kΩ, which is obtained from a
relation between the input RF-power and the intervane voltage derived from the
endpoint energy of X-rays generated from the cavity. The input power for accelerating
q/A ~ 1/28 ions is nearly 225 kW.
Transport line between RFQ and IH linac: A transport system between the RFQ and
IH linac comprises a rebuncher and two sets of quadrupole doublet. The rebuncher is a
25.96-MHz double coaxial quarter wave resonator with six gaps. The power
20

consumption in the cavity is less than 1.5 kW. The rebuncher operates at a 100-% duty
factor.
Spacing Rod
Beam
Cooling Channel
Back Plate
Stem Flange
Table 2-4. Main specifications of the TRIAC linac
Vertical Vane
Horizontal Vane
Window
Stem
Fig. 2-14. SCRFQ view (one of the four unit cavities).
IH linac: The IH linac accelerates ions with a q/A greater than 1/9 up to 1.09
MeV/nucleon. The IH is a separated function drift-tube linac (SDTL), which comprises
four tanks and three magnetic quadrupole triplets between tanks. Output beam energy
can be continuously varied by adjusting independently the phase and amplitude of the
RF field in each tank. The accelerating mode is π-π, and no transverse focusing element
21

is installed in the drift tubes. The achieved effective shunt impedances of the 1st through
4th tanks are 274, 268, 249 and 228 MΩ/m, respectively. From the measured shunt
impedances, we figured out the RF powers required for accelerating ions with q/A = 1/9,
i.e. 12, 22, 30 and 50 kW for the 1st through 4th tanks, respectively.
Magnetic Q-triplet Rf-Coupler
L-Tuner Ridge
Drift Tube
Fig. 2-15. IH view
Modifications of cavities: The SCRFQ [2-12] and IH linacs [2-13] primarily have
resonant frequencies of 25.5 and 51 MHz, respectively, while the JAEA Super
Conducting (SC-) linac has a resonant frequency of 129.8 MHz. We changed the
resonant frequency of the RFQ from 25.5 to 25.96 MHz and that of IH from 51 to 51.92
MHz for future’s connection to SC-linac. The resonant frequency of the RFQ was tuned
by changing locally interelectrode capacitance and stem (used for supporting the
electrodes) inductance. Values of the capacitance and inductance to be changed were
well estimated by using an equivalent circuit analysis; with the changed frequency, the
accelerating performance of the SCRFQ was shown to be kept except that the beam
energy changes from 172 to 178 keV/nucleon. The resonant frequency of the IH linac
was tuned by increasing the gap lengths between drift-tubes, that is, by decreasing the
capacitance. All drift-tubes were replaced to the modified ones. The gap lengths were
determined by model tests after rough estimations by MAFIA calculations.
2-4-2. Performances (obtained before the cavity modifications)
Transmission efficiency: The transmission efficiency of the RFQ was measured as a
function of the intervane voltage by using N2 + , N + and H2 + beams. Beam currents were
22
Stem

measured with Faraday cups, FC1, FC2 and FC3. FC1 is installed at the entrance, and
FC2 at the exit of RFQ. A quadrupole doublet is installed between FC2 and FC3. Under
the condition when the magnetic field strength of the quadrupole doublet is sufficient to
focus the accelerated ions into FC3, the transmission for the accelerated ions is obtained
from I(FC3) / I(FC1). Here, I(FCi) is the beam current from the i-th Faraday cup. The
transmission for the drift-through ions (containing unaccelerated ions) is given by
I(FC2) / I(FC1).
2-16. Transmission of the RFQ vs. intervane voltage
Fig. 2-17. Transmission along the accelerator.
The measured transmission is about 90 % at design voltage and agrees well with the
simulation by PARMTEQ [2-12]. From Fig. 2-16, it was verified that the intervane
voltage is applicable in a very wide range from 109 kV down to 1/14 of that voltage.
The transmission efficiencies of the RF/ IH linac were measured along the accelerator
23

y using N 2+ beam. For the measurement, FC4 and FC5 installed at entrance and exit of
the IH linac respectively were used as well as FC1 and FC2. The transmission of the
RFQ is nearly 95 % and that of the IH nearly 100 %, as shown in Fig. 2-17.
Energy and energy spread: We measured the output energy T and energy spread ∆T.
Figure 2-18 shows the output energy spectra measured at six operating modes, which
are described later. The IH-tank4 energy agrees well with a designed one, 1.053
MeV/nucleon. In Table 2-5, the measured T and ∆T values are compared with the
calculated values in parentheses. ∆T is defined by 2-rms of the spectrum containing
90% ions. The measured energy spreads are smaller than calculated one except for the
RFQ mode and variable modes.
Fig. 2-18. Energy spectra for six operating modes
Table 2-5. Energy and its spread for six operating modes. Numbers in parentheses are from
calculations. The results summarized here were obtained before frequency modifications
Different accelerating modes: The linac is operated at different accelerating modes to
change the output energy. For example, the IH-tank2 energy in Table 2-5 was obtained
24

y turning off the supply of RF power for the tank3 and tank4, and a variable energy by
adjusting the RF power voltage and phase in tank4. Deceleration test of the RFQ beam
was conducted by using the IH-tank1, in order to extend the variable-energy range. In
the experiment, He + beam was injected at a decelerating phase of 135 o of the IH-tank1,
and the output energy and its spread were measured as a function of the IH-tank1 RF
voltage. Figure 2-19 shows that the minimum energy is 112 keV/nucleon at a
normalized voltage of about 1.8.
Fig. 2-19. Energy and its spread vs. normalized voltage.
RF stability: The RF power sources have an automatic gain and phase control system,
in which a feedback signal is picked up from the forward power to the cavity. As for the
forward power, voltage variation is within 0.25 %, the phase one within 0.2 o . However,
we cannot ignore the voltage and phase variations in the cavity due to the temperature
change. We added three feedback systems to compensate the temperature change effect
on the RF voltage and phase in the cavity. One is a piston-turner control system for
tuning the cavity. The piston tuners are moved automatically so as to minimize the
reflected power from the cavity. The control system comprises the circuits for reading
the reflected power levels, the tuner driver circuits, and a personal computer. The
second is for keeping the cavity RF level constant in long-term by adjusting a control
signal (DC voltage) for RF output at a ten-second interval. The third is for constantly
keeping the phase difference between different cavities, the test result shows the phase
stability is within 0.2 o .
We have found the instability of the RF power supplied for SCRFQ. The instability
is associated with two components of voltage fluctuation: one is caused randomly in a
few minutes (slow component) and another is by electronic noises synchronized with
AC line (50 Hz component). The slow and 50 Hz components of the cavity voltage
fluctuation are shown by two red curves (one is in the inset) in Fig. 2-20, and the
magnitude of them corresponds to 20 % and 8 % of the nominal cavity voltage,
25

espectively. By modulating the control voltage signal for RF output so as to keep the
cavity voltage constant, both components were reduced to 2 % in magnitude. The RF
power stabilization system is now well operational for the stable beam delivery at the
TRIAC.
Fig. 2-20. Time variations of the cavity voltage are compared before and after introducing feedback
control for RF output. The short-term variations are given in the inset.
2-4-3. Simulation for upgrading output energy [2-14]
The present SCRFQ / IH complex can accelerate RIBs with a charge-to-mass ratio
(q/A) greater than 1/9 from 2.1 keV/nucleon to 1.09 MeV/nucleon. In order to increase
the beam energy up to 5-8 MeV/nucleon, we have made a plan to connect the IH linac
to the 129.8-MHz JAEA SC-linac existing at the Tandem facility. Although the plan has
not yet been realized, the frequencies of the SCRFQ and IH linacs have been already
changed from 25.5 to 25.96 MHz and 51 to 51.92 MHz, respectively, so as that their
frequencies become equal to 1/5 and 2/5 of the SC-linac frequency. The performance of
the 51.92-MHz IH linac was confirmed by the beam simulation using TRACEP code
[2-15]. After the beam simulation for normal operation based on the design, our
attention was paid on the special operation to bring the output beam energy to the
maximum restricted by the accelerating voltage limit. As a result of the simulation for
normal operation, the relation between output beam energy and synchronous phase of
the first accelerating cell is obtained for each tank. This relation is efficiently used as a
standard for adjusting the accelerating voltage and phase in the real operation of the
linac. Most importantly, by a subsequent simulation for the special operation, we show
that the IH linac could accelerate ions with a q/A = 1/4 up to 1.4 MeV/nucleon higher
than designed energy of 1.09 MeV/nucleon.
26

Encouraged by the new finding, as the most realistic solution for output energy
upgrade at TRIAC, we have examined the possibility for directly connecting the present
IH to the SC-linac. A most suitable energy for injection into the SC-linac is about 2
MeV/nucleon. However, we investigated the possibility of 1.4 MeV/nucleon injection
from the following reasons: 1) It is found that the IH linac is able to accelerate ions with
a q/A = 1/4 up to 1.4 MeV/nucleon with a tolerable reduction of beam quality for the
beam energy higher than designed, 2) Connection of the TRIAC to the SC-linac can be
realized with a significantly reduced cost and time, if it is found to be unnecessary to
construct a new linac for boosting the IH energy to 2 MeV/nucleon.
Fig. 2-21. Relation between input and output energies of SC-linac.
Fig. 2-22. Beam transport from IH to SC-linac
27

The JAEA SC-linac comprises 10 cryostats and 9 magnetic quadrupole doublets
set between cryostats. Four super-conducting cavities made of niobium are installed in
each cryostat. The cavities are 129.8-MHz two-gap λ/4 resonators. The optimum ion
velocity is 10 % of light velocity for all cavities. This linac has large velocity
acceptance, since the number of accelerating gap per cavity is only two and RF phase of
each cavity can be independently adjusted. The relation between input and output
energies were calculated for the cases of q/A = 1/4 and 1/7 under the condition that the
gap voltage is 375 kV and the accelerating phase -20 o at first gap. Figure 2-21 shows
that the SC-linac can accelerate ions with the injection energies higher than 1.1
MeV/nucloen. When the injecting energy is 1.4 MeV/nucleon, the maximum energy is
~ 7 MeV/nucleon for ions with q/A = 1/4.
A designed beam-transport line between IH and SC linacs is 37.71 m in total
length, and comprises 19 quadrupole magnets, two 45 o deflection magnets and two
25.96-MHz rebunchers [2-16]. Performances of the beam transport line were examined
by means of the beam simulations using MAGIC code [2-17]. The results are shown in
Fig. 2-22. The obtained important results are as follows: Beam transmission efficiency
from IH entrance to SC linac exit is 67 %. If 129.8-MHz buncher and 259.6-MHz
sub-harmonic buncher for injecting the tandem beam into SC linac are used instead of
two rebunchers, the efficiency is 40 %. From above results, it is concluded to be a
realistic plan to connect the TRIAC to the SC linac by using only existing devices
without constructing newly a booster linac and two rebunchers.
Test experiments: As mentioned above, a slight modification of acceleration mode of
the IH linac, especially final two acceleration stages of the IH linac, has been simulated
for higher maximum energy than designed: The higher energy could allow us to further
accelerate RI beams by SC-linac without additional equipments related to acceleration,
such as re-buncher and pre-booster between the IH and the SC linacs. The simulation
was confirmed by a test operation; indeed the maximum energy can be increased from
1.1 to 1.4 MeV/nucleon at the present facility. For the SC-linac where at least 2
MeV/nucleon at the injection is required for the effective acceleration, on the other hand,
a 40 Ar 10+ beam injected from the JAEA tandem accelerator was successfully accelerated
from 1.4 to 4.53 MeV/nucleon. It should be noted, however, that in this scheme the
beam transport and acceleration efficiency of the SC-linac is lower than what is
expected in the ideal case. Therefore, the present conclusion resulting from the test
experiments and simulations should be taken as a first step for step-by-step realization
of the ideal plan.
28

2-4-4. Development of superconducting low-β resonators [2-18]
As mentioned earlier for the specification of the post-accelerators at the TRIAC
(see subsection 2-4-1), the cavities were modified to match the resonant frequency of
the superconducting resonators (129.8-MHz two-gap λ/4 resonators) of the JAEA
SC-linac (i.e. from 25.5 to 25.96 MHz, from 51 to 52.92 MHz for the SCRFQ and the
IH, respectively), where the injection energy of at least 2 MeV/nucleon is required for
the effective acceleration. Therefore, we need a pre-booster between the IH and SC
linacs for boosting the output energy of the IH (1.1 MeV/nucleon) to 2 MeV/nucleon,
although we have discussed in the previous subsection the possibility to connect the
present TRIAC to the SC linac by using only existing devices.
We have designed and fabricated a superconducting twin-quarter-wave resonator
(Twin-QWR) made of niobium and copper as a pre-booster at the TRIAC. It has 2 drift
tubes and 3 acceleration gaps, as shown in Fig. 2-23. The resonant frequency is 129.8
MHz, which is the same for the existing QWRs in the SC linac. The optimum beam
velocity βopt (= vopt/c) is 0.06.
Fig. 2-23. Cross sectional view of Twin-QWR.
29

mode, and this is the mode for acceleration. The measured frequency separation
between two modes is about 0.86 MHz, which is enough for stable operation. Table 2-6
presents the main parameters of the present Twin-QWR obtained from the measurement
and calculation. Figure 2-24 shows the transit time factors of Twin-QWR and QWR as a
function of beam velocity. The optimum beam velocity βopt of Twin-QWR is 0.06, and
βopt of QWR is 0.10. The beams accelerated by the present TRIAC have the velocity of
about 0.048×c (1.1 MeV/nucleon), which can be efficiently accelerated by the presently
developed Twin-QWR.
Transit Time Factor
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
Table 2-6. Main parameters of Twin-QWR
Beam from TRIAC(1.1MeV/u)
0 0.05 0.1 0.15 0.2
Beam velocity β(= v/c)
31
3gap Twin-QWR
2gap QWR
Fig. 2-24. Transit time factors of presently developed Twin-QWR and exiting QWR as a function of
beam velocity.
In the design of the inner conductor part, it is important to hinder frequency
instability. The frequency instability is mainly caused by a deformation of the top end

accelerating the radioactive ion beams from the present TRIAC (i.e. from 1.1
MeV/nucleon to 2 MeV/nucleon as an input energy for the SC linac).
2-4-5. Development of re-bunchers for energy up-grading of the present TRIAC
As mentioned in the previous subsection, the original project of the TRIAC was
made to connect the present TRIAC with the JAEA superconducting linac, increasing
the energy of the RIB to 5~8 MeV/nucleon. The beam transport line between them has
been designed, and Fig. 2-26 shows the calculated beam envelopes.
Fig. 2-26. Calculated beam envelopes between the TRIAC facility and the JAEA superconducting
linac. The charge-to-mass ratio of the beam is assumed to be 1/7. The horizontal and longitudinal
beam profiles are shown in the upper half (blue and green lines, respectively), and the vertical profile
(red line) is shown in the lower half. The symbol “G” indicates a re-buncher. The narrow and wide
boxes indicate a quadrupole and dipole magnet, respectively.
Fig. 2-27 (Left) Cold model of the re-bunchers to transport RIBs from the present TRIAC to the
JAEA SC-linac (Right) Correlation between the resonance frequency and the partition plate position
of the re-buncher model.
34

Two re-bunchers need to be newly constructed, and a cold model of them has been
made and tested. Figure 2-27 (Left) shows the model of the bunchers. The cavity has a
double coaxial structure with a movable partition plate to tune the resonance frequency.
Figure 2-27 (Right) shows the correlation between the resonance frequency and the
partition plate position. The resonance frequency of 51.814 MHz, which is required to
match the RIBs from the TRIAC to the JAEA SC-linac, has been achieved by adjusting
the partition plate position. The electric field in the model has also been measured and
compared with the calculation.
2-4-5. Beam pre-bunching system [2-22, -23]
A beam pre-bunching system has been recently installed for producing a pulsed
beam with a width of less than 10 ns and an interval between 250 ns and 500 ns. The
use of the pulsed α beam is essential for the experiment (RNB-KJ04) to directly
measure the 12 C(α, γ) reaction cross sections at a highly reduced γ-rays background
expected in the proposed experimental set-up.
The system consists of a multi-layer beam chopper and a two-gap pre-buncher,
respectively installed at the F2-chamber and just upstream of the SCRFQ linac, as
shown in Fig. 2-28.
F2 Chamber
SCRFQ
Fig. 2-28. Layout of the beam line upstream of the SCRFQ, where the beam pre-bunching system is
installed
35

Fig. 2-29. Photos of the pre-buncher; outside view (Left panel) and inside view (Right panel).
The pre-buncher, as shown in Fig. 2-29, has two gaps at both ends of a single drift
tube respectively applied by a RF-wave synthesized with three harmonics (from the first
to the third), which are combined together into a pseudo saw-tooth wave-form for beam
bunching. By adjusting the length of the drift tube to be 140/360 in units of βλ
according to the beam-bunching frequency, where β is the velocity of the beam (2 keV/
nucleon at the TRIAC) normalized by the light velocity and λ is the wavelength of the
applied RF-waves for beam bunching, the pseudo saw-tooth wave could be properly
applied to the beam passing through the two gaps. In this way, the frequency of the
bunched beam can be varied between 2 and 4 MHz (i.e. variable time interval from 250
ns to 500 ns).
The beam test of the pre-buncher at a 2-MHz operation was performed using 16 O 4+
and 12 C 3+ beams supplied by KEKCB. The time structures of the beam observed with
buncher-on and off are compared in Fig. 2-30. At the buncher-off operation was
indentified 13 bunches of the beam by the acceleration frequency of 26-MHz SCRFQ
during the time interval of the frequency of 2-MHz (500 ns) beam-bunching (blue line
in Fig. 2-30). When the pre-buncher was on, a clear bunch structure (bunched into the
middle of 13 bunches with an interval of 500 ns) was observed at a target position 10 m
away from the exit of the TRIAC (red line in Fig. 2-30), although there exist a small
fraction of the beam failed to be bunched (i.e. observed as a side bunch instead of the
main, central bunch).
The bunching efficiency, defined as the intensity ratio of a bunch of beam (central
bunch in Fig. 2-30 when the pre-buncher is on) to the sum of 13 bunches with
buncher-off, was found to be 42 %. Incomplete beam bunching, partly observed as a
remainder of the 26-MHz operation of SCRFQ in Fig. 2-30 with buncher-on, is due to
36

the imperfect saw-tooth wave-form for beam-bunching. A fraction of the beam, 47 % in
the present observation, was lost during acceleration and not observed in Fig. 2-30. The
remaining fraction of 11% was properly accelerated but observed in the side bunches as
shown in Fig. 2-30. The present observations are well described by the beam simulation
code based on the TRACEP [2-15].
Fig. 2-30. Beam bunch structure with buncher-on (red line) and buncher-off (SCRFQ time structure)
(blue line).
Fig. 2-31. Front view of the multi-layer beam chopper on the beam direction
37

For the proposed experiment, the portion of beam in the side bunches, especially
during the time of 200 ns ahead of the main bunch of beam, should be less than 10 -4
relative to the intensity of the main bunch. Such contribution can be removed by the
operation of the chopper installed upstream of the pre-buncher, avoiding beam injection
into the buncher during the shaping time of the saw-tooth wave-form for beam bunching.
The chopper consists of 19 electrodes of thin plates, which are vertically piled on top of
each other against the beam injection at regular intervals of 1.9 mm, as shown in Fig.
2-31. The plate is made of phosphor bronze, which is 10-mm long along the beam
direction, 40-mm wide in the horizontal direction and 0.1-mm thick in the vertical
direction. The beam can be deflected upwards and downwards by applying an electric
potential to every two plates; every plate on the ground potential is sandwiched between
two plates on an electric potential. Time profile of the applied voltage is shown by red
line in Fig. 2-32. It should be noted that the fast-rising and -falling wave-form of the
applied potential (around 50 ns) is essential to keep the bunching efficiency high while
significantly reducing the portion of beam arriving prior to the main bunch of beam.
Thanks to the multi-layer structure, the applied voltage required for proper
deflection of beam becomes as low as about 120 V and the leakage of the electric field
along the beam direction is minimized, while about 14% of beam is lost by hitting the
electrodes. The beam chopped by the applied potential was injected into the SCRFQ and
turned out to be well accepted for acceleration; only during the time duration of
potential-off, the accelerated beam was observed, as shown in Fig. 2-32.
Fig. 2-32. Time profile of the potential applied to the chopper electrodes (red line by left vertical
axis), compared with the time structure of chopped beam after SCRFQ acceleration without beam
bunching beam (blue line by right vertical axis).
38

Fig. 2-33. Time structure of the bunched beam with the operation of the chopper (black) and without
the operation (grey)
The time structures of the bunched beam with chopper-off and -on are compared in
Fig. 2-33. There are not observed the beam for 250 ns prior to the central bunch,
indicating that the suppression of beam in the time range is better than 5x10 -5 . The
bunching system has been recently applied for the experiment.
2-5. Beam transport line
The beam transport line at the TRIAC can be divided into three sections, a
low-energy beam transport line (LBT: before acceleration), a beam transport line for the
SCRFQ / IH linac (ACC: during acceleration) and a high-energy beam transport line
(FBT: after acceleration).
2-5-1. Low energy beam line (LBT)
Ion optical configuration of the JAEA-ISOL, located upstream of the LBT, is
EQ-EQ-MD-ED, where EQ, MD, and ED stand for electric quadrupole, magnetic dipole,
and electric dipole, respectively. The mass resolving power of the JAEA-ISOL is M/∆M
= 1200.
After mass-separated by the ISOL, the singly charged RIB is transported to the
KEKCB by the first part of LBT whose optical configuration is shown in Fig. 2-34. The
designed acceptance is 200π mm•mrad. Two beam profile monitors, BPM-LBT01 and
BPM-LBT02 as shown in Fig. 2-34, are installed for stable ion beams. Formed in a
crossed wire and driven by a stepping motor, the monitor can probe simultaneously the
vertical and horizontal components of the beam profiles, when crossing the beam along
39

a diagonal direction. The monitors are followed by Faraday cups, FC-LBT01 and
FC-LBT02, respectively. For monitoring the intensity of RIB just upstream of the
KEKCB, a plastic scintillator (2 x 2 x 2 cm 3 ), SCI-LBT01 in Fig. 2-34, is installed in
the injection side of the KEKCB. It was covered by an aluminum plate of 100-µm thick
where the RIB was implanted. The detection efficiency for β-rays from the implanted
RIBs is about 50 %.
After being charge-bred, the RIB with a higher charge state is transported through
the second part of LBT to ACC. The ion-optical configuration between the KEKCB and
ACC is also shown in Fig. 2-34. The first component of 2MQ-MD-2MQ is dedicated to
charge state analysis of ions extracted from the KEKCB. The resolving power of
mass-to-charge state ratio (A/q) is designed to be (A/q)/δ(A/q) = 128 for the beams with
emittance of 100π mm•mrad. Three Faraday cups (FC-LBTFi, i = 1, 2, 3) and three
plastic scintillators (SCI-LBTFi, i = 1, 2, 3) are installed at F1, F2 and F3 chambers. A
beam profile monitor, BPM-LBT04, is installed between F1 and F2 chambers. The
designed acceptance of the second part of LBT is also 200π mm•mrad. Figure 2-35
shows the result of ion optical simulation with an initial emittance of 200π mm•mrad by
using the GIOS code.
Fig. 2-34 .Ion transporting optical components and beam monitors for low energy beam transport.
40

upstream of the target position not only for picking up timing information of beam
particles, one by one, but also for monitoring beam intensity during experiments.
Table 2-7 shows the present transport efficiencies of the respective transport lines
for 16 O 2+ and 129 Xe 19+ beams. The transport efficiency from ISOL to CB is almost
100 % for various ion beams.
2-5-3. Transport for charge-bred ions
In transporting charge-bred ions at the TRIAC, we have found that the transport
efficiencies for highly charged ions are significantly reduced. This is mostly due to the
charge-exchange collisions of highly charged ions during the beam transportation
through the 15-m long low-energy beam line. Such collisions with residual gases in
flight tend to transform the highly charged ions to lower charge states by electron
captures.
Fig. 2-37. Fraction of charge states measured at F3 for Xe 19+
In order to reduce the electron capture rates of highly charged ion beams in flight as
much as possible, higher vacuum in the low-energy beam line is necessary. To obtain
better vacuum, we installed eight cryopumps along the beam lines, 4 for LBT and
another 4 for SCRFQ. The averaged vacuum pressure in LBT was improved from
2×10 -4 Pa to 1.5×10 -5 Pa after the installation. The charge state distributions of Xe 19+
after its flight with 2 keV/nucleon from F1 to F3 (see Fig. 2-34) are compared under
different conditions of vacuum in Fig. 2-37. In this measurement, we selected the initial
42

charge state of xenon ions by using the analyzing magnet for the KEKCB. As shown in
Fig. 2-37, the escape fraction to lower charge states reduced from 70% to 20% in the
case of the 129 Xe 19+ .
Table 2-7. Beam transport efficiencies on each transport line.
LBT (CB -> ACC) ACC FBT
16 O 2+ 95 % 89 % 100 %
129 Xe 19+ 85 % 73 % 65 %
2-6. Control system
In order to operate the TRIAC, we have three control rooms which are dedicated to
the control of the devices for low-energy beam, accelerated beam and experimental
measurement, respectively. The equipments for low-energy beam consist of ISOL,
KEKCB, low-energy beam transportation line (LBT). Those for accelerated beam
consist of SCRFQ and IH linear accelerators (ACC.), and fast beam transportation line
(FBT). It is desirable to control almost all devices at experimental measurement room,
in order to transport stable and/or radioactive beams to user's experimental setup. Thus
we constructed a remote control system which connects the three control rooms through
a network.
Figure 2-38 shows the diagram of the control system. The interface programs of
control system are loaded in LabView (National Instruments Co. Ltd.) which is installed
in the personal computers (PC, Windows XP) in each control room. These PCs connect
via Ethernet to six board PCs, seven Field Point (FP) network modules, four GPIB
E-NET100 modules (National Instruments Co. Ltd.) and one programmable logic
controller (PLC) locally placed in the experimental hall and the power room. These
board PCs and FPs control some digital to analog converters (DAC) and motion-driving
modules which access to HV power and current suppliers for electromagnetic deflectors
and lenses, and motor drivers for some kind of beam monitors and RF tuners for
accelerators. The GPIB E-NET100 controls the devices which read the status of vacuum
gauges, magnetic field of deflectors and beam current of Faraday cups. The interlock
systems of beam and RF power generation are also controlled by FP modules. The
KEKCB control system belongs to another network group. A PC connects to the
sequencer which access to the devices for KEKCB operation. The ion source,
mass-separator and electric lenses for the JAEA-ISOL are operated independently at the
console. These elements are also controllable in any rooms by an additional PC having
DAC modules.
43

a thin film. Figure 2-39 shows a schematic view of the detector. It is composed of a thin
metalized Formvar film (~0.2 µm), an acceleration electrode, a drift space, a mirror
electrode, a two-layered MCP and a two-dimensional position sensitive board. When a
beam particle passes through the entrance film, secondary electrons are ejected, and
they are accelerated and reflected by high voltages applied to mirror electrodes. After
being multiplied by the MCP, they are captured on a readout board (2-dimensional
position sensitive board in Fig. 2-39) where the signals for position and timing
information are induced. The right panel of Fig. 2-39 shows the tracks of the secondary
electrons calculated under the electric potential generated by a high voltage
configuration, HV1 = -5500 V, HV2 = -4000 V, HV3 = -2300 V and HV4 = -100 V. It is
shown that positions of electrons ejected at the thin film are projected on the readout
board, well keeping the primary information on their emission positions. The
acceleration electrode and mirror electrode are composed of gold-tungsten wires of 20-
µm diameter stretched at intervals of 1 mm.
2-dimensional position
sensitive board
MCP
thin film
beam
acceleration
electrode
e −
mirror electrode
signal
HV4
HV3
HV2
HV1
Fig. 2-39. Schematic view of the beam diagnostic detector (left) and secondary electron tracks
under the electric potential distribution configured by high voltages that are respectively applied
to the electrodes (e.g. HV1 = -5500 V, HV2 = -4000 V, HV3 = -2300 V and HV4 = -100 V).
The two-dimensional position sensitive board has an area of 5 x 5 cm 2 . Figure 2-40
shows a part of the pattern of the readout electrodes on the board. For position
measurements, there are two kinds of electrodes, x-cells and y-cells. All x-cells are
connected to each other by delay lines in a row, and the time difference between two
signals from both ends of the row gives the position hitted by secondary electrons along
the x-axis as defined by dotted lines in Fig. 2-40. In the same way, another position (y)
can be read by the y-cells. Since the total delay time in the row is 100 ns, the sum of the
delay times of two signals from both ends of the row (relative to the timing by a striped
45
5 cm

electrode as shown in Fig. 2-40) should be that value. Applying such criterion on the
detected events, we can identify real events among them, which include some
unintentional events induced by noises. Rejecting those unlike events can be applied up
to the beam intensity of a few tens of Mpps, i.e. the intensity of ~10 7 pps is the
maximum beam rates countable by the present MCP. For higher beam rates, such event
selection is not applicable because of multiple hitting. The timing-readout strip
electrodes are connected directly to each other, and give a reference time signal for the
starting point of delay-line signals.
timing-readout
x-readout
Fig. 2-40. Pattern of readout electrodes on the two-dimensional position sensitive board.
46
y-readout
(a) (b)
1 mm
x-cell
y-cell
Fig. 2-41. Position distributions for alpha particles measured with two different kinds of
masks: (a) a hole of the diameter 1.8 mm and (b) a diagonal slit of width 1 mm.

Using the alpha particles from a 241 Am source, position resolutions of the detector
were measured. Figure 2-41 shows the measured position distributions of alpha particles
with two different kinds of masks put in front of the thin film; (a) a hole of 1.8 mm in
diameter and (b) a diagonal slit of 1 mm in width. Fitting the distributions with
Gaussian ones, the position resolution was deduced to be 6.5 mm in full width half
maximum (FWHM). The present resolution is considered to be largely limited by the
small number of electrons primarily produced on the thin foil by the impact of alpha
particles. For heavier ions, the resolution could be improved. A simplified version of the
presently developed detector, where is used a collector of the secondary electrons
multiplied by MCP instead of the position sensitive board, has been used as a beam
counter (i.e. intensity monitor and time pick-up detector) providing beam trigger signal
at TRIAC experiments to be described in the section 3.
2-7-2. Development of an active target
For the experiments using RIBs whose intensities are at most about 10 5 pps at the
present TRIAC, it is very efficient to employ a gas counter (e.g. Multiple Sampling
Tracking Proportional Chamber: MSTPC) as an active target [2-24], where the
operating gas for the counter played simultaneously the role of gas target for the nuclear
reaction of interest. Using such a detector, the detection efficiency for reaction products
of charged particles could be in principle100 % and the excitation function could be
measured at a fixed incident-energy of RIB. However, the gas-gain instability in the
MSTPC was observed under an injection rate higher than ~10 3 pps due to space-charge
limitation around anode wires of the MSTPC. We have developed a new type of the
active target working at a beam injection rate as high as 10 5-6 pps.
For higher injection-rate capability, a thick foil of gas electron multiplier
(THGEM) with a thickness of 400 µm [2-25] was used to overcome the gain instability
of a multi-wire proportional counter. We examined the performance of various kinds of
THGEMs by using low-energy heavy-ion beam from the TRIAC. For the investigation,
we made a new counter called as GEM-MSTPC, which consists of a drift space (active
volume of 100 3 mm 3 ), one (or more) THGEM, and an anode plate. The anode plate (Pad
in Fig. 2-42) is composed of backgammon-type electrodes (24 segmented pads) to
measure trajectories of charged particles in the horizontal plane against the vertical-drift
space. The drift times of electrons primarily produced from the position of a particle’s
track are measured, giving the position of the particle trajectory along the drift direction
of electrons (i.e. vertical position of the particle track). Figure 2-42 presents a
photograph of the GEM-MSTPC. The typical operating gas and its pressure are He +
47

CO2 (10 %) and 16 kPa, respectively, for the measurement of the 8 Li(α, n) 11 B reaction
cross sections. The gas gain on the THGEM was measured under the condition of the
operating gas. The measured gas gain was high enough (~10 3 ) in the single THGEM
configuration [2-26, -27].
Fig. 2-42. (Left) The photograph of the GEM-MSTPC. The drift space has two electrodes and is
enclosed by field-guiding wires (100 x 100 x 100 mm 3 ); ‘Top’ is a plate electrode and ‘Bottom’ is an
electrode which supports insulating pillars. ‘Pad’ indicates an anode plate, segmented for having
position sensitivity. (Right) The (vertical) configuration of the electrodes in the GEM-MSTPC is
shown, where the beam comes into the middle of the drift space (across the position of 50mm among
the vertical length of the 100 mm.)
When the GEM is incorporated in a 3-dimensional tracking detector, it is known
that the vertical position of the particle track is distorted by ion feedback [2-27]; the
electron drift time is disturbed due to the electric field induced by numerous ions
drifting away from the proportional region in gas amplification around the GEM into
the drift space. In order to suppress the ion feedback from the GEM foil to the drift
space, the double GEM configuration was finally adopted as shown in the right panel of
Fig. 2-42. Such a configuration helps reduce the operational gas-gain on the one GEM,
subsequently reducing the number of ions that back to the drift space.
We measured the time dependence of pulse height of anode output by injecting 4 He
from a radioactive source of 241 Am or the 12 C beam of 13.2 MeV provided by the
TRIAC. We observed shifts in the pulse-height with time, as reported in the previously
developed THGEM [2-25]. This phenomenon may come from the gas-gain instability
due to the electrical charge-up on the insulator between the GEM electrodes. It strongly
depends on the structure of holes punching through the electrodes. In order to avoid the
48

charge-up, we modified the structure of the holes and the surface of the electrode.
Table 2-8 shows a summary of such modifications together with observed
pulse-height shifts under various injection rates of particles with the energy of about 1
MeV/nucleon. THGEM #1 indicates the THGEM previously developed in Ref. 2-25,
which has an insulator rim of 100 µm in width around a hole. THGEM #2 has no rim
and the gain shift was suppressed to be less than 12 % under the 4 He injection rate of
10 4 pps. However, a discharge often occurred in several hours from the beginning of the
injection, and the gain became unstable once the discharge occurred. In order to avoid
the discharge, the diameter of the hole of THGEM#3 was reduced to be smaller than of
THGEM#2.
Table 2-8. Summary of modified THGEMs together with pulse height shifts at various injection
rates. THGEM#1 indicates the previously developed THGEM [2-25]. THGEM#2 has no rim on the
hole of 500 µm in diameter. The diameter of the hole of THGEM#3 was smaller than for
THGEM#2. The surface of copper electrodes was coated with gold for THGEM#4. ‘n/a’ indicates
not-measured.
Pulse
height
THGEM# #1 #2 #3 #4
Hole diameter [µm] 300 500 300 300
Rim yes no no no
Hole pitch [µm] 700 700 700 700
Electrode surface Au Cu Cu Au
4 He (E = 5.4 MeV, 10 0 pps ) 100 a few n/a n/a
4 He (E = 5.4MeV, 10 4 pps ) n/a 12 1~5 n/a
shift (%) 12 C (E = 13.2 MeV, 10 5 pps) n/a n/a 8 < 3
Fig. 2-43. Pulse-height shifts under the 12 C-beam injection rate from 400 pps to 10 5 pps using
THGEM #3 (left panel) and THGEM #4 (right panel). The horizontal axis indicates time from the
beginning of the beam injection.
49

Although the gain shift of THGEM#3 was suppressed to be within 5 % under the
same 4 He injection rate, it became larger (about 8 %) in the case of the 12 C injection rate
of 10 5 pps as shown in the left panel of Fig. 2-43. Moreover, the gain shift of
THGEM#3 gradually increased in several consecutive measurements with the 4 He
injection of 10 4 pps. Actually, the shift was about 1 % at the first measurement, whereas
it changed to be 5 % at the third measurement. This phenomenon could be explained as
the ‘ageing’ of the electrodes, such as oxidation of the surface of the copper electrode.
Hence, we coated the electrode of THGEM#4 with gold. THGEM #4 showed good gain
stability as shown in the right panel of Fig. 2-43. The pulse height became stable within
3 % under the 12 C injection rate from 400 to 1.2 x 10 5 pps.
The energy resolution under the 12 C injection rate of 10 5 pps was also measured. It
was obtained from the distribution of energy-loss signals from the segmented anode
pads. The energy resolutions under the injection rate of 400 pps of the two THGEMs of
#3 and #4 were almost similar (7% in σ). However, with the higher injection rate, e.g.
10 5 pps, THGEM #4 gave better energy resolution than THGEM #3; 8 % vs. 13 %.
The observed gain stability and energy resolution of THGEM #4 under the
injection rate of 10 5 pps satisfy experimental requirements. The GEM-MSTPC using
THGEM #4 (400-µm thick, 300-µm hole-diameter, Cu electrode coated by Au without
rim) was successfully employed to measure the 8 Li(α, n) 11 B reaction cross sections
(RNB-K05).
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[2-14] S. Arai et al., KEK Report 2008-8, 2008.
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51

3. Experiments at the TRIAC
Since the first public operation of the TRIAC, 50 days of operation per year, in
maximum, has been allowed for experiments, including the operation for 10 days for the
development of the RIB generation and acceleration at the TRIAC. The experimental
proposals were carefully reviewed, once a year, by the program advisory committee
(PAC). As listed in Table 3-1, 15 proposals have been approved and, among them, 13
proposals have been already performed. Two remaining proposals (KJ02 and KJ03)
have been already scheduled to be performed soon. There were 3 additional proposals
only using ISOL beams without reacceleration by post-accelerators.
The approved proposals are grouped according to relevant research field and
respectively summarized as followings: nuclear astrophysics (RNB-K01, K05, J01,
KJ03 and KJ04), nuclear and fundamental physics (RNB-K02/03, K04, and K08), and
materials science (RNB-K06, K07, J02/03, KJ01/02). The experiments using RIBs
without re-acceleration are also briefly described at the end.
3-1. Nuclear astrophysics
In recent decades, nuclear reactions involving the unstable nucleus 8 Li have
attracted considerable attention among nuclear physicists since they are considered to
influence largely the synthesis of heavy elements in neutron-rich high-temperature
environments. Such environments in the temperature of T9 = 1-3 (in unit of 10 9 K) could
happen, for example, in the early stage of supernova explosion and/or in the early
universe of inhomogeneous Big-Bang model. Continuous efforts have been made to
experimentally determine the relevant reaction rates at energies below the Coulomb
barrier. The low-energy 8 Li beam available at the TRIAC provides unique opportunities
to measure directly the relevant cross sections in the energy regime of astrophysical
interest.
The RNB-K01 (Spokesperson: H. Ishiyama (KEK) and T. Hashimoto (JAEA),
Collaboration (Institution (number of collaborators)): KEK (9), JAEA (8), Osaka
Electro-comm. Univ. (3), Osaka Univ. (2), GSI (1), NAO (1)) was the first attempt to
measure the cross sections of 8 Li(d, t) 7 Li reaction, which has been thought to play an
important role in destroying 8 Li nuclei and therefore limiting the synthesis of elements
over the mass of 8. By using the 8 Li beam from the TRIAC, the measurements were
made at seven different energies of 0.18, 0.24, 0.30, 0.40, 0.46, 0.60, and 0.75
MeV/nucleon, respectively corresponding to center-of-mass energies (Ecm) of 0.3, 0.4,
0.5, 0.7, 0.8, 1.0, and 1.1 MeV. Those Ecm cover the Gamow peaks of T9 = 1-3.
52

Table 3-1. List of experiments performed at the TRIAC. Approved experiments are identified by the
subject numbers assigned; RNB-Kxx and RNB-Jyy indicate the subject number approved by the
KEK-PAC and the JAEA-PAC, respectively. Additional experiments numbered by RNB-KJxx are
approved recently by a joint PAC.
Subject No. Title of subject Spokesperson(Affiliation)
RNB-K01 Direct measurement of astrophysical reaction rates through 8 Li H. Ishiyama (KEK)
RNB-K02/K03 Nuclear spectroscopy through β-delayed decay of spin-polarized nuclei
around doubly magic nucleus 132 Sn
The typical intensity was 1x10 5 particles per second (pps), energy resolution 0.85 % in
standard deviation (σ), and diameter of beam spot at the target position 3.4 mm in σ.
A deuteron target (deuterated polyethylene (CD2)) with a thickness of 130 µg/cm 2
was used. The detection system employed in the measurements is shown in Fig. 3-1.
Figure 3-2 shows the measured cross sections together with previous results [3-1].
The present experiment provides the first data in the low-energy region below Ecm = 1.5
MeV and covers the Gamow peaks in the temperature range of T9 = 1-3. An
enhancement was observed at around Ecm = 0.9 MeV in the excitation function, where
the cross sections are significantly larger than at the higher Ecm.
Figure 3-3 shows the resultant reaction rate, which is compared with the rate
estimated by the extrapolation of data at higher energies [3-1].
53
Y. Hirayama (KEK)
K. Matsuta (Osaka Univ.)
RNB-K04 R&D for a test of time reversal symmetry using polarized nuclei J. Murata (Rikkyo Univ.)
RNB-K05 Measurement of the 8 Li(α, n) 11 B reaction cross section for astrophysical
interest
T. Fukuda (Osaka
Electro-Com.Univ.)
RNB-K06 Local fields at 111 Cd implanted in Highly Oriented Pyrolytic Graphite W. Sato (Osaka Univ.)
RNB-K07 Diffusion Coefficient Measurements on Perovskite-type Structured
Lithium Ion Conductor
S. Takai
(Tottori Univ.)
RNB-K08 Search for highly excited states of 11 Be via 9 Li+d reaction T. Teranishi (Kyushyu Univ.)
RNB-J01 Search for highly excited states in 10 Be using deuteron elastic reaction to
RNB-J02/J03
RNB-KJ01
8 Li
Diffusion studies in Li ionic conductors by using short-lived radioactive
beam of 8 Li
RNB-KJ02 In-situ measurements of Li diffusion in Li micro-batteries & Nano-scale
diffusion experiments in Li ionic conductors by using 8 Li
H. Miyatake
(JAEA/KEK)
H. Sugai (JAEA)
S.C. Jeong (KEK)
H. Ishiyama (KEK)
S.C. Jeong (KEK)
RNB-KJ03 “Extremely” safe Coulomb excitation of 142 Ba N. Imai (KEK)
RNB-KJ04 Measurement of the cross section of 12 C (a,γ) reaction H. Makii (JAEA)

Fig. 3-1. Schematic view of the detection system for studying the 8 Li(d, t) 7 Li reaction. The
recoiled tritons were measured by using the ∆E-E telescope (43-µm-thick double-sided Si detector
and 375-µm-thick Si detector with a size of 50 x 50 mm 2 ), SSD1 and SSD2 (375-µm-thick Si
detector with a size of 18 x 18 mm 2 ). The scattered 7 Li particles were measured by SSSD1 and
SSSD2 (68-µm-thick single-sided Si detector a size of 50 x 50 mm 2 ) in coincidence with SSD1 and
SSD2. The beam intensity was monitored and its amount was measured by the plastic scintillator
installed just downstream of the Al plate, on which the beam particles were implanted after passing
through the target.
Fig. 3-2. Excitation function of cross section of the 8 Li(d, t) 7 Li reaction. The red circles show the
results of the present study. The open triangles show th results of the previous study [3-1]. Energy
regions of astrophysical interest are indicated by temperatures corresponding to the Gamow peaks
(red arrows).
54

The reaction rate deduced from the data shown in Fig. 3-2 is faster by about one order
of magnitude at about T9 = 1 than the previously reported values. The fast reaction rate
is due to the resonance like structure in the excitation function of the reaction observed
at around Ecm = 0.9 MeV. The reaction rate of the 8 Li(d, t) 7 Li reaction is 3x10 3 cm 3 /s,
which is 45 times larger than those of the 8 Li(n, γ) 9 Li [3-2] and 8 Li(α, n) 11 B [3-3]
reactions at around T9 = 1.
Fig. 3-3. Reaction rate of the 8 Li(d, t) 7 Li reaction as a function of temperature . The red line
indicates the present result and the blue line represents the result of Balbes et al. [3-1].
The present result indicates that the 8 Li(d, t) 7 Li reaction could suppress the
synthesis of heavy elements through 8 Li when the number density of deuteron (Yd) is
comparable to those of neutron (Yn) and/or α particle (Yα). However, in the process of
nucleosynthesis in type II supernovae presently considered as a candidate of
astronomical sites for synthesizing heavy elements by rapid neutron captures (r-process),
the suppression would be negligible since the estimated Yd/Yn and Yd/Yα values are
very small at T9 =1 (about 10 -6 and 10 -8 , respectively). Figure 3-4 shows an example of
such considerations [3-5], where the relative reaction rates (YxY8Li) were
calculated and compared for several 8 Li-involved reactions. In the calculations, the
fraction of light elements, Yx (i.e. proton (Yp), deuteron (Yd), neutron (Yn) and alpha
particle (Yα)) were deduced by a network calculation for the r-process using the
neutrino-driven wind model in the Type II supernovae [3-6]. The environmental initial
parameters (i.e. electron fraction, entropy, etc.) in the model were selected to reproduce
55

-element abundances up to the third (A ~ 195) peak. For easy comparison, the fraction
of 8 Li, Y8Li was assumed to be unity. As can be seen in Fig. 3-4, at T9 > 3.7, the 8 Li(p,
α)αn reaction is the fastest reaction, which destroys the 8 Li. In T9 = 0.7 – 3.7, the 8 Li(α,
n) 11 B reaction becomes the fastest one, which leads to the synthesis of heavier elements
than 8 Li. However, The relative rate of 8 Li(d, t) 7 Li is negligibly small as compared to
that of 8 Li(α, n) 11 B, and therefore the 8 Li(d, t) 7 Li gives little effect to the r-element
abundances in this model, although the reaction rate is relatively high. Nevertheless, our
present reaction rate of the 8 Li(d, t) 7 Li reaction should be included in the network
calculation for more accurate estimate of r-element abundances especially when using
other competitive astrophysical models for the calculations, since the astrophysical site
for the r-process is still controversial.
Fig. 3-4. Relative reaction rates (YxY8Li) of several 8 Li-involved nuclear reactions. The Yx is
the fraction of light element, x (x = n, p, d, α), and the Y8Li is the fraction of 8 Li. The reaction rates
of the 8 Li(d, t) 7 Li reaction estimated by using our present results were adopted, as shown in Fig. 3-4.
The rates of 8 Li(α, n) 11 B, 8 Li(p, α)αn, 8 Li(n, γ) 9 Li are from Ref. [3-3], [3-7], and [3-2], respectively.
The RNB-J01 (Spokesperson: H. Miyatake (JAEA/KEK), Collaboration: KEK (6),
JAEA (5), Kyushu Univ. (1), Tsukuba Univ.(1), Ibaraki Univ. (1), Osaka Univ. (2),
Osaka Electro-Comm. Univ. (2), CNS (1)) was dedicated to study the nuclear structure
around the resonant-like peak in the excitation function of 8 Li(d, t) reactions around Ecm
= 1.0 MeV previously observed at the RNB-K01 (as shown in Fig. 3-2). The energy
56

corresponds to an excited state of 22.4 MeV in 10 Be, which was also reported as a
proton/triton decaying state both in the neutron capture experiment of 9 Be and in the
resonant particle decay spectroscopy of 7 Li + 7 Li. It has been recently suggested that the
state might be a candidate of a coexisting cluster state with cluster structures of (α+t+t)
and (α+α+n+n) [3-8], which are of great importance not only for understanding the
clustering phenomena in neutron rich nuclei but also for an accurate estimate of the
reaction rate linked with such a state in the process of nucleosynthesis. The aim of this
experiment is to determine the spin and parity of this state, by using the thick-target
resonance elastic scattering of deuteron by 8 Li as shown in Fig. 3-5.
Fig. 3-5. Experimental set-up and principle of the thick-target elastic scattering method for
resonance-searching.
Following the PAC recommendation, a feasibility test for this measurement has
been performed for 3 days. A schematic figure for the experimental set-up and the
measurement principle is shown in Fig. 3-5. An elastic scattering with thick target was
employed in the inverse kinematics to search for the resonance states. The 8 Li beam of
0.94 MeV/nucleon with an intensity of 4.5 kpps passed through a time pick-up detector
(C-foil + Micro-Channel Plate (MCP) in Fig. 3-5) bombarded to the CD2 target of 2.6
mg/cm 2 in thickness. The energy of the scattered particles was measured by a set of
Solid State Detectors (SSD), and their time-of flight (TOF) between the MCP and SSD
was also measured. As shown in Fig. 3-6, where the correlations between the energy
and the TOF for detected particles were plotted, scattered deuterons were successfully
identified. In the figure were also observed tritons, 8 Li particles passed through
pin-holes on the target, and α-particles from decaying 8 Li, in addition to deuterons.
These particles were well resolved. Based on the present result, we can conclude that
the thick-target elastic scattering method for resonance-searching is feasible with the
beam intensity of 8 Li presently available at TRIAC (i.e. higher than 100 kpps). For
57

higher reliability of the experimental method, it would be desirable that the present
detection system should be extended to cover larger angles; it allows better statistics and
more experimental information at larger angles, if any.
Fig. 3-6. Correlations between the energy and the time-of-flight (TOF) for detected particles by
MCP and SSD (θLab.= 0). Different particles are localized in their own way and well identified, as
indicated by groups in the figure.
The RNB-K05 (Spokesperson: T. Fukuda (Osaka Electro-Comm. Univ.), H.
Ishiyama (KEK), Collaboration: Osaka Electro-Comm. Univ. (3), Tsukuba Univ. (4),
KEK (8), JAEA (7), Osaka Univ. (1), CNS (4), GSI (1), NAO (1)) was proposed to
measure the cross sections of 8 Li(α, n) 11 B reaction. This reaction is considered to be a
key reaction for heavy-element nucleosynthesis, since it bridges the gap of atomic mass
number of A = 8 in the stellar element abundance. We had already measured the cross
sections in the energy range of Ecm = 0.7 – 2.6 MeV [3-3], which corresponds to the
Gamow peaks of T9 = 1 – 3. In the measurement, we used a recoil mass separator
(RMS) as an in-flight fragment separator for producing the 8 Li beam, and employed a
gas counter (Multiple Sampling Tracking Proportional Chamber: MSTPC) as an active
target, where the operating gas for the counter played simultaneously the role of gas
target for the nuclear reaction of interest, and neutron detectors [3-9]. The cross sections
were about two times smaller than those of previous inclusive measurements where
only 11 B were measured, and a resonance-like structure in the excitation function was
58

successfully employed to measure the 8 Li(α, n) 11 B reaction cross sections. The 8 Li beam
with an intensity of 3x10 4 pps on average was injected into the GEM-MSTPC for about
3 days at the TRIAC.
Neutron counter
GEM-MSTPC
8 Li beam
Fig. 3-8. Experimental set-up for the measurements of 8 Li(α,n) cross sections. The beam of 8 Li is
counted one-by-one by the MCP and then injected into the GEM-MSTPC, where the occurrence
of the reaction (sudden change of the energy loss by recoil 11 B) is identified and the
simultaneously emitted neutron is measured by the neutron counter.
Although the intensity was limited by the data acquisition rate allowed in the
experiment because of unexpectedly low reduction rates of the veto counter installed
downstream of the GEM in order to remove beam particles without inducing reactions
of our interest (i.e. elastic scattering), the average injection rate is about 10 times larger
than that in our previous measurement using the RMS. In the experiment, the width of
the pad reduced by a factor of three as compared that in the precious measurement at the
RMS (but with the same operating pressure of the active gas) allows narrower beam
energy binning, accordingly higher energy resolution for Ecm in the measurement of the
excitation function. The picture of the experimental set-up is shown in Fig. 3-8.
The trigger for data acquisition was generated from the coincidence of signals of
the MCP and the neutron counter wall. Since neutron detectors had significant room
background, recorded data were mainly composed of accidental events. In order to
identify true reaction events, first of all, it is necessary to search for events with a
sudden change in the energy loss along the particle trajectory identified by the
60
MCP

GEM-MSTPC among the accumulated data. Figure 3-9 shows a typical example of true
reaction. The data analysis for selecting true reaction events on event-by-event bases is
in progress.
Fig. 3-9. Typical event pattern of 8 Li(α, n) 11 B reaction. (Left): Energy losses measured by pad
(dE/pad) are presented as a function of the number of anode pads, where the beam comes in from the
low pad number. (Right): Horizontal (x) and vertical (y) positions of the three-dimensional particle
trajectories, where the beam direction was defined as the z-axis (i.e. increasing pad numbers in the
figures).
Using a stable ion beam of 4 He provided by the TRIAC, the RNB-KJ04
(Spokesperson: H. Makii (JAEA) and H. Miyatake (JAEA), Collaboration: KEK (9),
JAEA (5), RIKEN (1), Osaka Univ. (1)) was proposed to directly measure the 12 C(α,
γ) 16 O reaction cross sections and determine the strength of electric-dipole (E1) and/or
-quadrupole (E2) components in the α-capture cross sections (decaying strength of
excited 16 O by emitting γ-rays of corresponding multi-polarities) at stellar energies. The
reaction plays an important role at the stage of helium-burning in stellar evolution; its
reaction rate determines the mass fraction of 12 C and 16 O after the stellar helium-burning,
the abundance of elements from oxygen to iron, and the iron-core mass before
61

supernovae explosion [3-11]. Therefore, it is quite important to accurately determine the
cross section at Ecm ≈ 0.3 MeV corresponding to the stellar temperature of interest. The
direct measurement of the cross section at Ecm ≈ 0.3 MeV, however, is not possible with
current experimental techniques, because the cross section is too small, around 10 -17
barn. Hence one has to estimate the cross section by extrapolating the cross sections
measured at energies higher than 1.0 MeV into the region of corresponding energies,
and the extrapolations rely on theoretical calculations that gave scattered results
according to their theoretical approaches. Consequently, the estimated cross section at
Ecm ≈ 0.3 MeV has a large uncertainty, which turned out to be largely due to the poor
experimental determination of the relative strengths of E2- to E1-radiative capture
reactions (σE2 / σE1) at higher energies.
Recently, it has been shown that the ratio of σE2 / σE1 could be determined with a
good accuracy by using high-efficiency anti-Compton NaI(Tl) spectrometers to detect
the γ-rays from the reaction, where a pulsed α-beam was employed to discriminate true
events from background events induced by neutrons from 13 C(α,n) 16 O reaction with a
time-of-flight (TOF) method and the target thickness and α-beam intensity were
monitored during the measurement by the Rutherford backscattering spectrum of
α-particles from the target [3-12, -13]. In order to provide a stringent constrain to the
extrapolation down to Ecm ≈ 0.3 MeV, the present proposal aims at measuring the ratios
at several energies, where large discrepancies have been observed in the values of the
ratios predicted by various theoretical calculations, by using the experimental set-up in
Ref. 3-13. The measurements would provide good insight into distinguishing between
different calculations, and thereby help reduce the large uncertainty in the
extrapolations.
In the proposed experimental set-up, the use of the pulsed intense α beam is
essential for reducing the background γ-rays induced by neutrons originating from the
13
C(α,n) reaction; the background γ-rays can be removed because they have a delayed
detection time as compared to the prompt γ-rays of interest. The pulsed beam with a
width of less than 10 ns and an interval between 250 ns and 500 ns was developed for
the experiment at the TRIAC. We fabricated a beam-bunching system consisting of a
pseudo saw-tooth wave pre-buncher and a multi-layer chopper, and tested the
pre-buncher with a repetition frequency of 2 MHz using 16 O 4+ and 12 C 3+ beams with the
same mass-to-charge ratio as 4 He 1+ from the TRIAC. A clear bunched structure with a
width of 2 ns in standard deviation was observed at a target position 10 m away from
the exit of TRIAC [3-14]. Incomplete beam bunching, observed as a remainder of the
26-MHz operation of SCRFQ was removed by the operation of the chopper installed
62

upstream of the pre-buncher, avoiding beam injection into the buncher during the
shaping time of the saw-tooth wave-form for beam bunching [3-15].
Fig. 3-10. Experimental set-up for the measurements of 12 C(α,γ) cross sections. Three NaI(Tl)
detectors are placed at 40 o , 90 o , 130 o relative to the beam direction. The scattering chamber was
installed at the center of the detectors and includes a water cooled target holder where several
12 C-enriched targets on the gold foil backing were set. The vacuum in the chamber was about 10 -7
Pa.
Fig. 3-11. Correlation in the energy and the time of γ-rays measured by the NaI(Tl) detector at 40 o
using bunched α-beams of 0.701 MeV/nucleon. Vertical and horizontal axes correspond to the
observed γ-ray energies in unit of MeV and the times-of-flight from the RF signals in unit of
nanosecond, respectively. Intensities of correlated events are presented by different colors as
indicated in the right-hand side of the figure. Events in the red circle indicate the characteristic γ
transitions from excited state populated by the reaction to the ground state in 16 O.
Using the beam-bunching system and experimental set-up shown in Fig. 3-10, the
experiment has been recently performed at four incident energies ((0.701, 0.774, 1.12
and 1.13 MeV/nucleon) of the α-beam. Figure 3-10 shows the experimental set-up,
which is similar to the one in Ref. 3-13 except for a water cooled target holder for the
63

pure (99.9 %) 12 C target. A monitor SSD was set at 77 cm upstream of the target to
measure elastically backward scattered α particles, whose energies reflect the effective
thickness and uniformity of the irradiated target. Typical beam intensity was 5 µA.
Irradiation times at 0.7 and 1.1 MeV/nucleon are 5 and 2 hours, respectively.
Figure 3-11 shows one of the measured correlation spectra for the energies and the
times-of-flight of detected events by NaI(Tl) detectors. The start trigger of the
time-of-flight measurement was the RF signal (26 MHz) from the TRIAC. The
characteristic γ-rays of about 9 MeV decaying from excited states in 16 O can be found at
around 200 ns as a part of prompt events, which are strongly correlated to the arrival of
the pulsed α-beam. Such prompt events are clearly separated from delayed γ-ray events
starting from around 210 ns; the present observation well demonstrates the successful
operation of the beam pre-bunching system (no beam bunches prior to the main bunch
as shown in Fig. 2-33), otherwise the prompt γ-rays around 9 MeV would be hindered
the delayed γ-rays. Some low-energy, randomly existing γ-rays were also observed,
which indicates that their origin are related to the thermal neutron capture reactions by
the contaminants around target or in detectors (e.g. γ-rays of 6.8 MeV originate from
127
I(n, γ) reactions induced by thermal neutrons in the NaI(Tl) detectors). The reaction
cross section will be deduced for those prompt events with γ-ray energy of 9 MeV.
Further analysis is in progress.
3-2. Nuclear and fundamental physics
The following experiments to study nuclear structure and fundamental physics
were carried out using the radioactive ion beams (RIBs) provided by the TRIAC: (1)
RNB-K02/K03: Nuclear spectroscopy through β-delayed decay of spin-polarized nuclei
around doubly magic nucleus 132 Sn (Spokesperson: Y. Hirayama (KEK) and K.
Matsuta (Osaka Univ.), Collaboration: KEK (9), JAEA (6), Osaka Univ. (5), Niigata
Univ. (2), Kochi Univ. of Tech. (1), RIKEN (1)). (2) RNB-K04: Test of time reversal
symmetry using polarized nuclei (Spokesperson: J. Murata (Rikkyo Univ.) and Y.
Hirayama (KEK), Collaboration: Rikkyo Univ. (9), KEK (3), JAEA (2), and RIKEN
(1)). (3) RNB-K08: Search for the highly excited state in 11 Be via 9 Li + d reaction
(Spokesperson: T. Teranishi (Kyushu Univ.) and H. Ishiyama (KEK), Collaboration:
KEK (6), JAEA (7), CNS/Univ. of Tokyo (1), Osaka Univ. (2), and Tsukuba Univ. (1)).
These experiments are respectively summarized in the following subsections. The status
of the RNB-KJ03 (Spokesperson: N. Imai (KEK)), which is to be carried out soon,
will be presented at the end of this section.
64

The process of nuclear polarization by the TF technique is schematically shown in
Fig. 3-13: The tilted-foil method uses the anisotropic atomic collision of incident ions
with the conduction (constituent) electrons at the exit surface of the foil. When the ion
beams passing through a thin foil, tilted against the incident beam direction at an
oblique angle (θ in Fig. 3-13), the electronic states of the outgoing ions are polarized.
Polarization is initially introduced in the orbital motion of the electrons by the surface
interaction at the instant of exit of ions from the foil. During flight in free space, some
of this electron spin (J) polarization is transferred to the nuclear spin (I) through
hyperfine interaction. The direction of the polarization is well defined; n x v where n is
the unit vector normal to the surface of the foil at the exit and v is the ion’s velocity. By
a successive passage of several such foils, interspersed with regions of free flight to
allow a significant nuclear precession around the total angular momentum F=I+J in
flight, the polarization effect is enhanced. In this way, rather sizable nuclear polarization,
~10 %, for a wide variety of elements can be achieved [3-18].
The features of this method can be summarized as follows: The method is
applicable to any elements and the RIBs of a few hundred keV/nucleon are considered
to be most suitable for the effective capture of electrons, which is essential for the
primary atomic polarization. The degree of polarization increases with the number of
foils [3-19] and the tilted angle between the beam axis and the axis normal to the foil
surface [3-20]. The direction of polarization is easily reversed by reversing the normal
axis of the foil surface. The degree of nuclear polarization PI induced by the multi-foil
can be approximated as follows [3-21],
N { Q } PJ
I + 1
PI ( N)
~ 1−
.
J + 1
Here, N is the number of foils, I and J are respectively nuclear and atomic spin, PJ is the
degree of atomic polarization and Q is expressed approximately for small PJ by:
2 2
1− 2/
3⋅
J / I if I / J > 1 , 1 / 2 if I / J = 1 , 1 / 3 if I / J < 1 . From the nuclear
polarization measured as a function of the number of foils, dominant atomic state for the
atomic and nuclear polarization could be estimated by using the equation for PI.
Experimental setup: Figure 3-14 shows a schematic side view of the experimental
setup for the production and measurement of nuclear polarization. Reaccelerated RIBs
pass through a stack of tilted-foils in vacuum chamber. After being spin-polarized by the
TF method, they are implanted into a catcher (often called as catcher or stopper foil),
where a magnetic field B0 is applied to preserve the nuclear polarization. The catcher
can be cooled by a refrigerator (down to about 10 K, if necessary) in order to achieve
66

much longer spin-relaxation time than the lifetimes of RIBs (necessary condition for the
measurement of nuclear polarization by β-NMR method). It is the most critical to
choose the catcher that is suitable for each RIB to hold the nuclear polarization during
their lifetimes, otherwise the nuclear spin would be depolarized before measurement. A
radio-frequency (RF) oscillating field B1 for the NMR measurement is generated by the
RF coils fixed around the catcher. The emitted β-rays are detected by the double layered
plastic scintillator telescopes in the atmosphere, which are placed above and below the
catcher. Nuclear polarization PI is evaluated from the up/down ratio W(0 o )/W(180 o ),
where W(θ) is the angular distribution W(θ) ~ 1 + APcosθ of emitted β-rays from
polarized nuclei. Here A and θ are the asymmetry parameter of β-transition and the
emission angle with respect to the nuclear polarization axis, respectively.
Fig. 3-14. Schematic side view of the experimental setup for polarization by the TF method and
β-NMR measurement
Figure 3-15 shows: (a) the photos of the experimental setup, (b) a polystyrene foil
on a non-magnetic copper ladder and (c) a stack of 20 polystyrene foils with tilt angle
70 degrees, respectively. The area of each foil is 45 mm x 15 mm which corresponded
to 15 mm x 15 mm at the tilted angle of 70 o in view of the beam direction. The area is
about twice larger than the beam spot about 8 mm in diameter at the entrance of the
foils, considering the broadening of beam spot due to the multiple scattering when the
beam passes through in the multi-foils. The thickness of the foil is about 3 µg/cm 2 (~ 30
nm), and therefore the number of the stacked foils could be increased three times more
than those of the generally used carbon foils.
Polarization of 8 Li: The TF method has been studied in detail at the TRIAC by using
the 8 Li (τ1/2 = 838 ms, I π = 2 + , g = 0.8268) beam at various energies (140, 178 and 240
keV/nucleon). The 8 Li nuclei with a typical intensity of ~10 5 pps were implanted into an
67

annealed platinum foil (stopper foil), which is 10-µm thick and placed at room
temperature in the magnetic field of B0 ~ 0.05 T for holding the nuclear polarization.
The β-NMR technique was applied to the measurement of the nuclear polarization.
Ten carbon foils, each of which is of 10 µg/cm 2 in thickness and distant by ~1 mm
from each other, were used with a tilted angle of 70 o in the first experiment. The
polarization was observed to be 3.7 ± 1.1 % but it was not saturated with the 10 sheets
of foils. Although higher polarization is expected with increasing number of foils, the
carbon foils are so thick that the 8 Li beam cannot pass through more than ten foils.
Therefore, we developed thinner polystyrene foils (e.g. ~3 µg/cm 2 in thickness). In the
second and third experiments, the polarization of 7.3 ± 0.5 % was achieved at the beam
energy of 140 keV/nucleon by using 15 foils of polystyrene at the tilted-angle of 70 o .
Figure 3-16 shows the polarization as a function of the number of polystyrene foils for
various energies of incident 8 Li.
(a) (b)
(c)
RIBs
Stacked tilted-foils
20 foils @ 70o 20 foils @ 70o Magnet
B 0
Nuclear
polarization
68
45
15
Fig. 3-15. Photos of (a) the experimental
setup for the polarization of heavy
elements, (b) a polystyrene foil and (c) a
stack of the polystyrene foils. For the
polarization of 8 Li, we used a rather
simple configuration because much lower
holding field (Bo) was allowed (i.e. a
coreless electromagnet was used).

8 Li polarization : PI (%)
10
8
6
4
2
140 keV/A ( 70 deg. )
178 keV/A ( 70 deg. )
240 keV/A ( 70 deg. )
0
0 5 10 15 20 25 30
Number of foils
Fig. 3-16. 8 Li polarization as functions of sheet-number of polystyrene foils measured for incident
beam energies of 140, 178 and 240 keV/nucleon, respectively. The solid lines were given by fitting
the formula for nuclear polarization (PI) to the data. The data points observed with largest number of
foils at the beam energy of 140 and 240 keV/nucleon are largely deviated from the general tendency;
it might be related to an unintentional geometrical mismatch in the foil system, especially at the exit
of the foil (e.g. tilted angle, damped energy and broadened spatial distribution of the beam, etc.).
Except for the two data points, the data points seem to be well reproduced with the formula.
In the third experiment, we tested a new experimental set-up modified for the
polarization of the heavy nuclei around 132 Sn, as shown in Fig. 3-15 (a): The tilted-foil
system was modified to reduce the distance between the tilted-foil and stopper for
making possible simultaneous implantation of beam of several charge states after
passing through the stack of foils. The modified β-NMR system can operate at a high
magnetic field B0 ~ 0.5T (Holding field) and a high frequency for RF magnetic field
(oscillating transverse field). The operation of the system was confirmed by using the
8 8
Li beam. The polarized Li beam was applied for test of time reversal symmetry using
polarized nuclei (K04) described in the next section.
The solid lines in Fig. 3-16 show the fitted results using the formula, which is
given above for the polarization where the multi-foil effect is taken into account. In
fitting, we assumed the atomic spin of J = 1/2 for 8 Li ions, whose values actually govern
the dependence of the polarization on the number of foils. For example, the formula
becomes saturated with about 10 foils and cannot reproduce the experimental data when
the atomic spin of higher than J = 1/2 is assumed. It indicates that 2p ( 2 P1/2) state may
dominantly contribute to produce the polarization of 8 Li. In the presently used formula
69

the observed CP-violating phenomena in K-meson and B-meson system, predicts a
negligible effect on u-d quark (nuclear) systems. On the other hand, some models based
on physics beyond the standard model, predict visible size of CP-violating effects, i.e.
T-violating effects in normal nuclear system. Therefore, the observation of a non-zero
T-violating effect directly implies the evidence for a new physics beyond the standard
model. A triple vector correlation between nuclear spin J I
r , electron spin σ e
r and
momentum Pe r is a T-odd variable. Therefore, assuming time reversal symmetry, beta
r r r
decay rate must not depend on the R-correlation, defined as; σ e ⋅ 〈 J I 〉 J × P I e E . In the
e
standard model, R is almost zero. If non-zero R-correlation exists, electrons emitted
from the β-decaying polarized nuclei would have non-zero transverse polarization.
Therefore, experimental investigation of time reversal symmetry can be accomplished
by the measurement of electron momentum and its transverse polarization, using
β-decaying polarized nuclei [3-23, -24]. Figure 3-18 shows the principle of determining
electron transverse polarization. Electrons are emitted from the stopped nuclei and then
injected into a polarimeter, which is installed outside of the vacuum chamber. The
polarimeter utilizes the transverse analyzing power in the Mott scattering of electrons
from heavy nuclei (gold or lead foils). By measuring the ratio between electrons
scattered upward and downward, the transverse polarization can be determined.
Fig. 3-18. Principle of determining electron transverse polarization by observing up-down
asymmetry in backward scattering angular distribution.
The electron polarimeter using a drift chamber has been developed. Figure 3-19
shows the experimental setup. The polarimeter consists of trigger plastic scintillators
counters, a planer multi-wire drift chamber, and an analyzer foil of Pb (113-mg/cm 2
thick). The drift chamber is designed for tracking the trajectories of electrons; it
observes not only the tracks of the incident electrons, but also the second tracks of
electrons scattered backwards by the thin lead foil placed behind the chamber.
72

In the first experiment, the performance test of the polarimeter was carried out by
using unpolarized 8 Li beam of 178 keV/nucleon. The “V-track” events scattered from a
thin gold foil (10-µm thick, 300 mm x 500 mm in area) were successfully identified and
the observed angular distribution of the Mott scattering shows a good agreement with
the Mont-Carlo simulation taking into account the full detector system.
Polarimeter:
Drift chamber
Analyzing foil:
Pb
73
Polarized
8 Li beam
Stopping plastic counters
Fig. 3-19. Experimental setup. Electrons scattered at backward angles from the analyzer foil form
“V-track”s, which is detected by the planer drift chamber.
In the second experiment, the measurement of the R-correlation (i.e. the first
experimental test of the time reversal symmetry in nuclear beta decay of a polarized
nucleus) was examined. For the measurement, a new FPGA-based intelligent triggering
system (DC trigger) was installed in order to suppress the background events such as
Coulomb multiple scattering and X-ray radiation, which helps reduce significantly the
backgrounds by utilizing a V-track reconstruction technique on an event-by-event basis.
As a result, about 10 6 V-track events from polarized 8 Li nuclei have been successfully
recorded in the measurement. Thanks to the DC trigger, the purity of the real V-tracks
among the recorded events was improved by 10 times better than in the previous
experiment, and the live time of the data taking system was found to be almost 100 %
with a beam rate of ~10 5 pps. In order to cancel geometrical asymmetries of the
polarimeter, the spin direction of incident 8 Li beam is flipped every 5 minutes by
rotating the tilted foil angles. Totally 17-Giga 8 Li ions were implanted on the annealed
platinum stopper, which sandwiched by spin holding permanent magnets. About
1.6-Giga triggers by plastic scientillators were generated at a rate of around 12 kHz, and
finally 13-Mega DC-triggered events were recorded at only around 0.1 kHz. After the

offline data analysis, about 1-Mega V-track events were successfully reconstructed.
The Mott scattering angular distribution is shown in Fig. 3-20, for both spin-up and
-down settings of the tilted-foil system for polarized 8 Li beam. If shapes of the
distributions are different from each other, it means that the time reversal symmetry is
violated. The value obtained from the preliminary analysis is concluded to be zero
within the present statistics.
Fig. 3-20. Angular distributions of the V-track events of electrons scattered backwards by the lead
foil.
The R&D for the test of the time reversal symmetry using polarized 8 Li nuclei at
TRIAC [3-25] is successfully performed, as the first measurement using event-by-event
V-track reconstruction without suffering from dominant backgrounds. The present
system developed for the experiments at the TRIAC, shows a good performance as an
electron transverse polarimeter which is going to be used at the TRIUMF. By utilizing
the 8 Li beam with higher intensity and better polarization (10 7 pps with 80 %
polarization) at the TRIUMF, the R-parameter will be determined with a precision of
0.01%. The project has been already started at the TRIUMF as S1183 MTV experiment
from 2009. First physics run is successfully performed in 2010 with highest statistical
precision, utilizing the experimental technique developed at the TRIAC.
3-2-3. Search for the highly excited state in 11 Be via 9 Li + d reaction (K08)
An excited level at 18.2 MeV in 11 Be has been suggested from observations of
beta-delayed deuteron, triton, and α emissions in 11 Li beta decay experiments [3-26].
This level is above and close to the 9 Li+d threshold at 17.9 MeV and possibly enhances
74

the beta-delayed deuteron emission probabilities [3-27] (Fig. 3-21). This level is also a
candidate of a “halo analog state” of 11 Li, which is populated by a Gamow-Teller (GT)
transition of the two halo neutrons in 11 Li, namely 11 Li ( 9 Li+2n) 11 Be* ( 9 Li+d) [3-28].
20.68
11 Li
β −
18.15
0
11 Be
75
17.916
9 Li+d
8 Li+t, 2α+3n,
6 He+α+n,
9 Be+2n, 10 Be+n
Fig. 3-21. Level diagram of beta-delayed particle-emitting 11 Li.
Clear determination of the energy, width, and spin-parity may be therefore useful for
studying the GT transitions of 11 Li and its halo structure. However the signature of the
level was not so clear in the beta decay experiments; the energy and width of the level
were deduced from the spectrum, which contained unresolved deuterons and tritons
without any well identified peaks, and from an unresolved 4,6 He spectrum in the decay
11 Li (β) 11 Be * 6 He+α+n, which did not show any peak corresponding to the level
because of the three body decay. Moreover, a recent observation of beta delayed
deuterons did not indicate any resonance signature [3-29]. Further experimental
investigation with a different approach is necessary.
Fig. 3-22. Experimental setup for studying 9 Li+d reactions.
In the present experiment we have studied 9 Li+d reactions to search for a
resonance signature attributed to the 18.2-MeV level. We measured deuteron, triton,
alpha spectra from 9 Li+d elastic scattering, 9 Li(d,t), and 9 Li(d,α) reactions, respectively.
The 9 Li+d reaction experiment was performed at the TRIAC. A primary beam of 7 Li at
70 MeV from the JAEA tandem accelerator bombarded an ISOL target of BN.

Secondary 9 Li ions extracted from the ISOL target were accelerated up to 0.85
MeV/nucleon. Figure 3-22 shows the experimental setup for the study of the 9 Li+d
reactions. The beam ions of 9 Li were counted on an event-by-event basis using an MCP
detector with a 0.1 mg/cm 2 Mylar foil. After passing through the MCP detector, the 9 Li
beam bombarded a (CD2)n target of 2.3 mg/cm 2 with an average beam intensity of
approximately 3×10 4 pps. To deduce the excitation functions of 9 Li(d,d), 9 Li(d,t), and
9
Li(d,α) reactions, we utilized a thick target method in inverse kinematics (TTIK),
where the target thickness was chosen to be thick enough to stop most of the incident
9
Li ions in the target. The recoil deuteron, triton, and α particles suffered relatively
small energy losses in the target and detected by a Si detector array (SDA) located
26-cm downstream of the target with its center at 0°. The SDA consisted of 3×3 Si
detectors, each of which was 300-µm thick and had a sensitive area of 28×28 mm 2 .
TOF(ns)
120
115
110 110
105
100
95
90
85
80
75
70
0 2 4 6 8 10 12 14
E (MeV)
Fig.3-23. E-TOF spectrum for recoil particles.
The particle identification was made by using time-of-flight (TOF) information
between the MCP and SDA and energy (E) information of the SDA. Figure 3-23 shows
an example of the measured TOF-E spectrum. There was a background component
below 2 MeV, which was due to accidental α particles from the beta decay of 9 Li. The
timing distribution of the accidental α particles was essentially uniform and their energy
distribution could be easily estimated. Then, the accidental background component was
subtracted from the deuteron, triton, and α spectra. Though analysis is in progress, a
preliminary result of the 9 Li+d spectrum contains no sharp peak but shows
monotonically increasing cross sections toward the low excitation energy side. A
76

possibility of resonance contribution to this spectral shape will be examined by utilizing
R-matrix analysis. The triton and α spectra will be analyzed on the same R-matrix basis
by assuming some resonance contributions.
3-2-4. Coulomb excitation of 142 Ba at 1.1 MeV/nucleon (KJ03)
Barium isotopes are located in an island of octupole deformation. The B(E2) and
B(E1) values in these nuclei give us crucial information on the correlations to the dipole
or quadrupole moments in nuclei. A recent lifetime measurement of the first 2 + (2 + 1)
state of 142 Ba gave a B(E2) value inconsistent with the previous experimental data
[3-30]. Up to date, the B(E2) values of 142 Ba have been measured by using the lifetime
measurements of the 2 + 1 state produced by the spontaneous fission of 252 Cf. The
inconsistency among the previous data can be attributed to how to take into account the
effects of cascade transitions and recoil velocities of fission products. Instead of lifetime
measurement, the KJ03 proposed the Coulomb excitation measurement of 142 Ba
employing the TRIAC. The TRIAC can accelerate radioactive isotopes extracted by the
JAEA-ISOL up to 1.1 MeV/nucleon, which is far below the Coulomb barrier. Thus, the
cascade transition can be negligible since the probability of multi-step excitation should
be very small.
As a test of the whole experimental system including charge-breeding electron
cyclotron resonance ion source (KEKCB), we performed an experiment of Coulomb
excitation with a stable 130 Ba beam of 1.1 MeV/nucleon. The energy of 2 + 1 state of 130 Ba
is 359 keV, which is close to the 357 keV for 142 Ba. Therefore, the present experiment
well simulates the measurement of 142 Ba.
A 130 Ba 1+ beam was supplied by the JAEA-ISOL using the enriched BaCO3.
Typical beam intensity was about 30 enA. The beam was injected into the KEKCB for
charge-breeding the singly charged ions 130 Ba 1+ to multi-charged ones 130 Ba 19+ . The
charge breeding efficiency was around 1%. The 130 Ba 19+ beam was transported to
post-accelerators of the TRIAC and accelerated to 1.1 MeV/nucleon.
At the final focal plane of the TRIAC, a secondary target of 2-µm thick nat V was
placed and irradiated by the beam. 6 NaI(Tl) detectors of 9 x 9 x 18 cm 3 were placed to
detect the de-excitation γ rays from the excited 130 Ba around the target. The NaI(Tl)
detectors were mounted in the 2-cm thick lead box to suppress the background γ rays or
X rays. To measure the recoiled particles, an annular type SSD of a large solid angle
was placed 18-cm downstream of the target. The detector covered from 12 to 24 o in the
laboratory frame, which corresponds to angles from 48 to 160 o in the center of mass
frame.
77

Fig.3-24. γ ray energy spectra coincident with SSD (solid line) and accidentally coincident with SSD
(dashed line).
Fig. 3-25. Set-up for the Coulex experiment. The set-up used for the 130 Ba experiment is given
schematically as an inset. The picture of the set-up at the experimental hall is also given, where part of
10 NaI(Tl) detectors surrounding the target (here Vanadium target) are visible. An annual SSD is
installed in the chamber downstream of the target. The beam passing through the target is monitored a
plastic scientillator for beta-decaying 142 Ba beam installed at the position of the FC for the stable 130 Ba
beam.
Figure 3-24 shows two γ-ray energy spectra measured by three NaI(Tl) detectors
with different timing gates. Solid line indicates the γ rays which were coincident with
78

the SSD, while dashed line represents the accidentally coincident γ rays; only a peak
around the energy of 360 keV was clearly observed as expected. Comparison of the
cross sections between elastic and inelastic scatterings yielded the B (E2;2 + 0 + ) = 0.97
(22) e 2 b 2 , which was in good agreement with the adopted value of 1.163(16) e 2 b 2 .
The beam development of 142 Ba was also performed independently. The beam
intensity can be expected to be several 10 3 particles/s at the secondary target. The
measurement of B(E2) value of the 2 + 1 state of 142 Ba is scheduled to be carried out soon.
For the experiment, the number of NaI(Tl) in increased from 6 to 10, by which the
detection efficiency for γ-rays of 360 keV becomes 14 %. The experimental set-up is
shown in Fig. 3-25.
3-3. Materials science
TRIAC can provide low-energy radioactive ion beams ranging from 2 keV/nucleon
to 1.1 MeV/nucleon with a small beam size, for example less than 10 mm in diameter,
but still with intensity high enough for experiments. Thanks to these characteristics, we
can implant the RIBs into samples of interest, usually small in size, with an
implantation depth well-suited for specific experimental requirement.
Over more than half a century, diffusion studies in solids using radioactive tracers
[3-31] have played an important role in understanding the underlying mechanism of
atomic transport in solids, which is of great importance in a number of branches of
materials science and engineering. Although the conventional radiotracer method for
diffusion studies in conjunction with a serial sectioning technique [3-32] has yielded the
most accurate diffusion coefficients, the method has not yet been applied for some
elements because of no-availability of radiotracers with adequate lifetimes. Among
them, 8 Li, the radioactive isotope of Li with a half-life of 0.84 s is of special interest for
practical issues; how well Li ions move in the secondary Li ion batteries. Fast Li
diffusion is desirable in battery materials, i.e., Li ionic conductors for materials of
electrodes and solid electrolyte. For studies on the macroscopic diffusivity of Li in Li
ionic conductors, various electro-chemical methods [3-33] have been usually adopted
up to now. However, the diffusion coefficients are scattered over several orders of
magnitude, strongly depending on the method used for the measurement [3-34].
Therefore, the diffusion coefficients measured in different ways, e.g. by using the
radiotracer of Li, are highly required to settle down such disagreements. Such an
experimental knowledge on the Li diffusion in as-developed materials for the battery is
also of importance in the recent general efforts to design the battery by simulations
based on the first principle.
79

In the experiments of RNB-J02/03 (Spokesperson: S.C. Jeong (KEK), H. Sugai /
M. Sataka (KEK)), Collaboration: (KEK (8), JAEA (7), Aomori Univ. (2), NIMS (3),
Osaka Prefecture Univ. (1), CNS (1)), it has been found that the short-lived radioactive
beam of 8 Li at the TRIAC successfully operates as a diffusion tracer in the lithium ionic
conductors. This kind of application has been performed for the first time over the
world. In the experiment, we measured α-particles, emitted from β-decaying 8 Li,
coming out of the sample of interest after implanting RIBs, and have found that the
time-dependent yields of α-particle from the diffusing 8 Li primarily implanted is a good
measure of the lithium diffusion in the sample.
The radiotracer 8 Li decays through β-emission to 8 Be with a half lifetime of 0.84 s,
which immediately breaks up into two α-particles with energies continuously
distributed around 1.6 MeV with a full width at half maximum (FWHM) of 0.6 MeV
[3-35].
Figure 3-26 shows schematically the principle of the measurement: Implanting the
beam of 8 Li with a properly adjusted energy into a depth, deeper than the average range
of α-particles, we can make a situation where most α-particles stop in the sample. After
implantation, since the primary implantation profile is broadening with time by
diffusion, the α-particles emitted by 8 Li diffused toward the surface can survive and
come out of sample with measurable energies. Then a charged particle detector, located
close to the sample surface, could selectively detect α-particles from 8 Li diffusing
toward the sample surface, since the implantation-depth is deeper than the average
range of α-particles in the present case. Therefore, the temporal evolution of α-particle
yields that come out of the sample is supposed to be a measure of the diffusivity of Li.
Fig. 3-26. Principle of diffusion measurements by implanting 8 Li-RIBs.
80

Provided by the TRIAC, the radiotracer beam 8 Li of about 4 MeV with an intensity
of about 10 4 particles/s was periodically implanted to the sample of interest with a
following time sequence; 1.6 s for implantation (beam-on) and of 5.1 s for subsequent
diffusion (beam-off). The α particles coming out of the sample were measured as a
function of time by an annular solid-state detector (SSD). The SSD with a central hole
was installed close to the front surface of the sample as shown in Fig. 3-27. The
sequence was repeated to obtain good statistics, where the time-zero was always at the
beginning of the implantation. Before starting the measurement, the sample was set at a
temperature where the diffusion coefficient was supposed to be measured. It should be
noted that the present diffusion time is different from that of the conventional method
[3-36] because the tracer in the present method diffuses all the time of the measurement.
This is the reason why we call the present method an on-line measurement of diffusion.
Fig. 3-27. Experimental set-up. The energetic and pulsed tracer beam of 8 Li are implanted into the
sample and the decayed α particles are measured as a function of time by the solid state detector
located in front of the sample. The condition of the tracer beam is given, which includes energy,
intensity, repetition frequency of the pulsed beam and its duty factor.
Figure 3-28 shows time spectra of the yield of α-particles measured at different
temperature for the stoichiometric LiIn. Properly normalized for comparison, the spectra
are presented by the ratios, i.e. time-dependent yields of α-particles divided by the α
radioactivity of 8 Li at the time of interest. In this way was excluded the trivial
time-dependency in the yield of α-particles just depending on the lifetime of 8 Li. If 8 Li
does not diffuse at all, the values of the ratios should be constant over time. However,
the experimental values as shown in Fig. 3-28 show different time structure depending
on the temperature, well demonstrating that the time structure is a good measure of the
macroscopic diffusivity of 8 Li at the temperature where the measurement has been
performed. Based on this relative time-dependency of α-particle yields (time dependent
81

atio), a diffusion coefficient was estimated by comparing with the simulation where
one-dimensional Fickian (Gaussian) diffusion was assumed [3-34,-37].
Fig. 3-28. Time spectra of α-particle yields measured at various temperatures for LiIn. The spectra
were corrected for removing trivial time dependence and further normalized properly for easy
comparison.
Fig. 3-29. Temperature-dependence of diffusion coefficients (closed symbols) and electrical
resistivity (open symbols) for β-LiGa with 44 at. % Li, and β-LiIn with 48 % at. Li.
The diffusion coefficients of Li in β-LiGa and β-LiIn with a near stoichiometeric
composition of Li, are displayed in Fig. 3-29 as a function of inverse temperature. For
both samples, the diffusion coefficients suddenly change at a certain temperature,
following Arrhenius behavior in the region of higher temperature. The sudden change in
the value of the diffusion coefficient occurs at the temperature where the anomalous
electrical resistivity is observed. The resistivity measurements were carried out using a
van der Pauw method as used for β-LiAl [3-38]. This observation is closely related to
82

the thermal properties of the structural defects, already observed as the anomalies in
heat capacity [3-39, -40] and nuclear-spin lattice relaxation [3-41] at 233 K near the
critical composition of the Li-deficient β-LiGa. It has been suggested that these
phenomena are related to order-disorder transformation of the Li vacancies in the
compounds.
The ordering of the vacancies would produce a sharp drop in the Li diffusion
coefficients below the ordering temperature since the vacancies are supposed to be the
carriers of Li atom. The observed amount of change, more than two orders of magnitude
in the value of diffusion coefficients in the case of β-LiGa, is quite impressive as
compared to those observed in the measurement of electrical resistivities where just a
small change (at most 1/10) can be seen at the transformation temperature. The
transition temperature is known to shift to lower temperature, and the change in the
electrical resistivity becomes invisibly smaller with increasing Li composition, where a
large fraction of the Li vacancies forms complex defects with anti-structural Li atoms
on Ga sublattices [3-42]. Therefore, with higher sensitivity, the present method could be
applied for better investigating the characteristics of the transformation that are
supposed to be correlated with the concentrations of structural defects strongly
depending on the Li compositions.
At the lower temperature followed by a sudden change around 234 (±2) K for
β-LiGa, the diffusion coefficients are observed as a constant, which is the lower limit of
diffusion coefficients accessible by the present method; for diffusion coefficients less
than about 10 -10 cm 2 /s, any significant effect in the yields of α-particles due to the
diffusing 8 Li could not be observed because of the short life-time of the radiotracer.
In Fig. 3-30, the time-dependent normalized α-particle yields are compared for
different Li compositions, i.e. 43.6, 50.0 and 53.2 at. % Li. Referring to the time
dependence of the α-particle yields, the stoichiometric β-LiGa has the highest
diffusivity of Li among three, most quickly rising and falling down. This observation is
quite different from those observed for β-LiAl and β-LiIn [3-43] which are
iso-structural with the β-LiGa.
The abnormal behavior of Li diffusivity in β-LiGa is well identified in Fig.3-31,
where the diffusion coefficients in β-LiGa at room temperature are presented as a
function of Li composition together with the data for β-LiAl and β-LiIn reported in Ref.
3-43. As shown in Fig. 3-31, the Li diffusion coefficients in β-LiAl and β-LiIn decrease
monotonously with increasing Li composition, but the correlation is changing due to the
coexistence of vacant Li sites VLi and antistructure Li atoms on the aluminum (or
indium) sites LiAl (or LiIn), as discussed earlier in terms of the size effect of constituent
83

Although the data for β-LiAl and β-LiIn were available only in a limited range of
Li composition from 48.3 to 53 at. % Li, it would be interesting to note that the
diffusion coefficients in β-LiGa varied in a similar way (increase with decreasing Li
content) between those values in β-LiAl and β-LiIn in the corresponding range of Li
composition. This would be intuitively understandable, since the iso-structural β-LiGa
with a comparable size of the constituent atoms should have an interaction between VLi
and LiGa with intermediate strength as compared to those discussed in the case of β-LiAl
and β-LiIn [3-43]. Therefore, the composition-dependence of Li diffusivity in β-LiAl
and β-LiIn could be considered as the lower and upper limits of the Li diffusivity in
β-LiGa over the Li composition range of interest, respectively: two complementary
explanations might be possible by referring to the respective composition-dependency
observed in β-LiAl and β-LiIn.
Referring to the tendency in β-LiIn, the diffusion of Li in very Li-poor β-LiGa
seems to be suppressed. This could happen, for example, by assuming the formation of
defect complex such as VLi-VLi and/or VLi-LiGa-VLi, since the concentration of VLi
become much (almost three times at maximum) larger [3-44] in the more Li-poor
composition than investigated in β-LiIn [3-43]. It should be noted that the number of
vacant Li sites in a unit cell volume (8 for Li and 8 for Ga) is about two for the most
Li-poor β-LiGa (43.6 at. % Li), whereas there exist about one vacant Li site in every
two-unit cells for the most Li-poor β-LiAl (48.3 at. % Li) and β-LiIn (48.4 at. % Li) in
Fig. 3-23. Here, we assumed the random distribution of the vacancies over the available
sites.
Alternatively, assuming the diffusivity of Li in the most Li-poor β-LiGa as a good
extension of the diffusivity of Li in the Li-poor β-LiAl (48.3 at. % Li) because of nearly
zero concentrations of LiAl and LiGa in the corresponding Li composition, the diffusivity
of Li observed around the stoichiometric β-LiGa could be considered to be enhanced by
the coexisting defects of VLi and LiGa. Under the coexistence of VLi and LiGa, the motion
of the vacancies on the Li site, supposedly the carriers of Li atom, seems to be strongly
promoted. This suggests that the interaction between VLi and LiGa would be stronger and
rather repulsive than expected by the atomic size effect, but not as strong as observed in
β-LiIn. In addition, as a specific characteristic of the interaction in β-LiGa, we found
strong composition-dependence of the interaction that appears to become stronger when
a comparable amount of two types of point defects exists.
In the present measurement, although we found abnormal Li diffusion in very
Li-poor composition of β-LiGa, the characteristic of the anomaly in diffusion, i.e.
whether the diffusion is suppressed or enhanced, is not conclusive. A detailed theoretical
85

consideration is highly required for quantitative discussion. From the experimental point
of view, however, it would be interesting to extend the measurement to the more
Li-poor composition of LiIn recently confirmed to have the β-phase in the same
composition [3-45] as investigated for β-LiGa in the present work.
Using the method mentioned above, tracer diffusion coefficient of lithium ions in
the perovskite-type structured lithium ion conductors (La2/3-xLi3xTiO3; LLTO) have also
been measured in the experiment of RNB-K07 (Spokesperson: S. Takai (Tottori Univ.),
Collaboration: Tottori Univ. (1), KEK (8), JAEA (4)). The diffusion coefficients were
consistent with those obtained by neutron radiography method [3-46] measured above
200°C (Fig. 3-32). The tendency that lower lithium concentration with higher A-site
vacancy possesses higher diffusion coefficients was confirmed around room
temperature. Additional experiments for the sample of x=0.166, which is A-site stuffed
composition, has been performed and the data analysis is in progress. In the experiments,
a quenched sample with higher crystal symmetry was also studied and would help
clarify the contribution of disordering of the vacancy.
s -1
D / cm 2
10 -5
10 -6
10 -7
Temperature, t /
500 300 200 100 50
o C
10
1 2 3
-8
T -1 / kK -1
Fig. 3-32. Arrhenius plots of diffusion coefficients of LLTO measured by radiography () and the
present 8 Li () methods. Red, blue and black symbols are for x = 0.066, 0.116 and 0.166,
respectively.
86

In the experiment of RNB-K06 ((Spokesperson: W. Sato (Kanazawa Univ.),
Collaboration: Kanazawa Univ. (1), KURRI (1), KEK (4), JAEA (2)), local fields at
111
Cd nuclei in Highly Oriented Pyrolytic Graphite (HOPG) has been investigated by
means of the Time-Differential Perturbed Angular Correlation (TDPAC) method. This
experiment was designed to investigate the physical and chemical states of isolated
atoms introduced in carbon allotropes. For the introduction of the probe 111 Cd nuclei, an
HOPG sheet was irradiated with a very-low energy (30 keV) radioactive nuclear beam
of A = 111 as parents. The observed TDPAC spectra were discussed in terms of lattice
damages produced when introducing the probe into the sample.
As an extension of the present method, the proposal of RNB-KJ02 considers the
possibility to trace the Li macroscopic behavior across the interface in hetero structural
Li ionic conductors in micrometer scale, to be termed 8 Li microscope.
The time spectra shown in Fig. 3-28 represent dynamical movement of Li in the
sample between as-implanted position and surface during a cycle for measurement. For
a single layer (diffusion in homogeneous sample) as discussed in case of Fig.3-26, the
present method can trace, most efficiently, the Li movement within one-dimensional
distance of about 10 µm for about 7 s. For slow diffusion, Li is still moving toward the
surface for the time of measurement, the α-particle yields are monotonically increasing
with time. For moderate diffusivity, a maximum is observed when Li is reflected by the
surface. After the maximum, the yield is simply decreasing with time since Li is
diffusing into the bulk. For double layers (hetero structural sample) whose interface
exist in between, i.e. introducing an interface between the as-implanted position and the
surface, we could observe time structure different from the case of single layer. In other
words, we could observe how Li interacts with the interface, e.g. if Li is precipitated,
perfect or half reflected on the interface. This idea could be applied to take a dynamical
picture of Li in Li ion micro-batteries consisting of thin films of several µm in thickness.
Therefore, the present method could be called 8 Li microscope by analogy with the
neutron transmission image of Li in a secondary Li ion battery, where the picture of Li,
actually 6 Li, in the battery was taken by the neutron radiography with a resolution of
mm [3-46].
For higher sensitivity, from microscale to nanoscale, the proposal of RNB-KJ02
also considers a coincident measurement of two α-particles emitted from position of
β-decaying 8 Li. The micrometer sensitivity of the method discussed so far is partly
coming from the broad energy distribution of α-particles on decaying. Therefore, the
coincident measurement is supposed to dramatically improve the sensitivity since the
87

coincident α-particles have the same energy at the decaying position. In diffusion
tracing method by 8 Li, however, a special attention is paid on the energy loss of
α-particles subjected to the actual path length in the sample of interest from the
decaying to the detection positions. For diffusion in a nanoscale, the diffusion length is
too short to give a significant change in the energy loss of α-particles. We further apply
a limitation in emission (detection) angles to the coincident measurement as shown in
Fig. 3-33. With small emission angles, the actual path length of α-particles in the
sample of interest can be made significantly longer than implanted depth, giving rise to
a considerable energy loss difference against a nanoscale diffusion length toward the
surface. Along with the idea, we have performed a simulation to examine the feasibility
and search for an observable most sensitive to diffusion profiles with a diffusion
coefficient of 10 -12 cm 2 /s, a specific goal of present consideration. The simulation was
performed in a similar way discussed in Ref. 3-34, by using the energy loss and
straggling of α-particles provided by the SRIM-code [3-47]. We assumed the diffusion
coefficient as 10 -12 cm 2 /s, the sample thickness as 50 nm, the emission angle as 5 o , and
the implantation energy as 1 keV.
Fig. 3-33. Schematic layout for a coincident measurement of two α-particles emitted with angles of
θ1=θ2 relative to the surface of sample. The actual path lengths (L1 and L2) in the sample are
enhanced 10 times as compared to those considered in Fig. 3-26 when applying limitation to the
emission angle of 6 o .
As a result of the simulation shown in Fig.3-34, we found that the energy
difference between two coincidently measured α-particles could provide nanoscale
sensitivity. The concentration profiles of 8 Li simulated sequentially with a condition
given above are shown in Fig. 3-34(a); the as-implanted profile is broadening with time
by diffusion. Simulated in the same time sequence as done for profiles, the spectra of
energy difference of two α-particles to be measured coincidently are compared in Fig.
3-34(b). There is a good correspondence between the diffusion profiles and energy
88

difference spectra, more specifically a clear one-to-one correspondence between
decaying position of 8 Li and energy difference of two coincidently measured α-particles.
For example, looking at the time evolution of the counts of coincident events with zero
energy difference in the energy difference spectra should be a good measure of the time
when 8 Li is across the middle of the sample, because the zero energy difference means
that the path lengths experienced by two coincident α-particles are identical. We can
conclude that the sensitivity against the diffusion of 10 -12 cm 2 /s could be easily achieved
by the coincident measurement of two α-particles with the geometry assumed in the
simulation.
Fig. 3-34 (a) Simulated concentration profiles of 8 Li implanted into LiCoO2 with a thickness of
50nm with an energy of 1keV and their evolution by diffusion simulated at 1, 2, 3 and 4 seconds
after implantation with a diffusion coefficient of 10 -12 cm 2 /s. (b) Spectra of energy difference of
α-particles coincidently emitted at angles of 5 o relative to the surface of the sample. They are
respectively simulated in the same time sequence as done in Fig. 3-34 (a).
The proposal of KJ02 has met difficulties in the fabrication of the samples with an
appropriate thickness and surface roughness, especially for the coincidence
measurements of two α-particles where the sample is required to have a form of a
self-support foil with a thickness of about 100 nm. After all considerations, the proposal
has been modified to confirm the feasibility with a reduced sensitivity (e.g. 10 -10 ~10 -11
cm 2 /s), as a simple extension of the previously developed method, by focusing the
time-evolution of the energy spectra of α-particles emitted with a large angle from
β-decaying 8 Li implanted with an energy of about 10 keV. An experimental set-up was
newly fabricated and is ready for an experiment to be carried out soon.
89

3-4. Experiments with the ISOL beam (without re-acceleration by the TRIAC)
The ISOL ion sources developed for the TRIAC could provide good opportunities
to perform some experiments by using the beam without re-acceleration. In this
subsection, two experiments for nuclear decay-spectroscopy study using the SIS with
UCx, and an experiment using the FEBIAD with an enriched 96 Mo target for materials
science are described.
3-4-1. Qβ measurements of 160-165 Eu and 163 Gd
Fig. 3-35. Fermi-Kurie plots of the measured total absorption spectra [3-48]. The data points used
for fitting and adopted lines are shown by closed circles and solid lines, respectively. The endpoint
energies and the deduced Qβ values are given in the figures.
90

Mass, which is one of the most fundamental quantities for atomic nuclei, provides
good insight on the evolution of the nuclear structure. In addition, the mass is one of the
key parameters to build the scenarios of nucleosynthesis in universe. The mass of
160-165 163
Eu and Gd isotopes have been determined for the first time by measuring Qβ
values using a total absorption BGO detector. Among them, isotopes of 163-165 Eu were
newly observed.
The isotopes produced by proton-induced fission of 238 U of about 600 mg/cm 2
thickness were ionized by the SIS and mass-separated by the JAEA-ISOL. The isotopes
were implanted onto an aluminum-coated Mylar tape, and were periodically moved to
the center position of the total absorption BGO detector. The detector composed of twin
BGO scintillation detectors of 120 mm in diameter and 100mm in length which faced
each other with a distance of 4 mm. The solid angle of the detector was 96 %. For
measurements of 160-165 Eu, the time interval of the tape transport was set to be two or
three times longer than the half-lives of these isotopes, while, in the case of 163 Gd, the
times for collection, cooling, and measurement were set by 4, 2, and 2 minutes,
respectively, to allow the decay out of the parent nucleus 163 Eu (T1/2 = 6 s), which has a
larger Qβ value than 163 Gd.
The Fermi-Kurie plots of the total absorption spectra of 158, 159 Pm, 159, 161 Sm
160-165 163 166
Eu, Gd and Tb are shown in Fig. 3-35. Qβ values of 158, 159 Pm, 159, 161 Sm, and
166
Tb were found to be consistent with our previous experimental results. The evaluated
Qβ values given by Audi et al. [3-49] were in agreement with the present results. The
mass predictions by Duflo et al. [3-50] and Dussel et al. [3-51] were also consistent
with the experimental values.
3-4-2. Lifetime measurements of 162, 164 Gd (2 + )
The collectivity is one of useful quantities to explore the vibration of the nuclear
structure. In the case of the even-even nuclei, the transition probability from the first 2 +
state reflects the quadrupole collectivity. The lifetimes of the first 2 + states at 71.5 keV
in 162 Gd and 73.3 keV in 164 Gd were measured by means of β–γ delayed coincidence
technique for mass-separated 162 Eu and 164 Eu isotopes.
As described previously, the fission products of 162,164 Eu were ionized by SIS
embedded UCx and transported to the tape system. The tape was moved every 20 s and
9 s for 162 Gd and 164 Gd, respectively. The detection position was equipped with a
Pilot-U 60 mm × 63 mm × 1-mm thickness plastic scintillator and a 38-mm diameter ×
5-mm thickness BaF2 scintillator to detect β and γ rays, respectively.
The time interval spectra for the first 2 + state in 162 Gd and in 164 Gd were obtained
91

as shown in Fig. 3-36 (a) and (b), respectively. These spectra include the prompt time
components from Compton events caused by higher-energy γ rays. The lifetimes were
deduced by fitting an exponential decay curve, a exp(-t/τ)+b , by a least-χ 2 method.
Contributions of lifetimes of higher-lying states are neglected because their lifetimes are
expected to be much shorter than that of the 2 + states. The lifetimes were determined to
be 3.98(8) ns and 4.0(2) ns, for 162, 164 Ga, respectively. Here, the errors were estimated
from the spread of various fitted values obtained by changing the fitting range. In
addition to these nuclei, the lifetime of the 2 + state in 160 Ga was also measured from β
delayed γ rays from 140 Eu. The resultant lifetime was 3.94(12) ns, which was in good
agreement with the previous result of 3.91(8) ns, well verifying the present experiment.
The measured lifetime were converted to B (E2;0 + 2 + ) values by taking into
account the total internal conversion coefficients αT taken from the ICC code in the
program [3-52], and the energies of the first 2 + state. The obtained B (E2;0 + 2 + )
values were deduced to be 5.45(11) e 2 b 2 and 5.2(3) e 2 b 2 for 162,164 Gd, respectively.
Fig. 3-36. Time interval spectra between β rays and γ rays from the fist 2 + state in 162 Gd (a) and
164 Gd (b), respectively [3-52]. The results of the fitting were demonstrated by the solid lines. See
the text for the details.
3-4-3. Time differential perturbed angular correlation in highly oriented pyrolytic
graphite (K06)
When a radioactive nucleus with a large quadrupole moment is implanted into a
material, the emission of radiation is affected by the (neighboring) magnetic field and/or
an electric field gradient at the implanted place. In addition, if the radionuclide emits
two gamma rays in cascade via an intermediate state whose lifetime is in order of ns, the
emission pattern reflects the dynamics of the internal material. In other words, we can
deduce the nano-scale structure concerning the extranuclear charge distribution, and
magnetic properties of the material by measuring the angular correlation between the
92

gamma rays. 111 In, which decays to 111 Cd with T1/2 = 2.8 days by emitting two cascade
gamma rays of 171 and 245 keV via an excited state of 85 ns, is well known as a probe
complying with the above condition. By accelerating 111 In by the TRIAC, the
implantation depth can be controlled, enabling us
to investigate the properties of material at
different depths. As the first step, we implanted
111
In into a highly oriented pyrolytic graphite
(HOPG) with 30 keV employing only the
JAEA-ISOL.
An enriched 96 Mo target of 3 mg/cm 2
thickness was irradiated with the 19 F beam of 95
MeV from the JAEA tandem accelerator. 111 In
produced by the fusion evaporation reaction, 19 F
( 96 Mo, 2p2n), was implanted into a HPOG plate.
Typical beam intensity was about 10 4 pps. After
20-hours implantation, we measured the
time-differential perturbed angular correlation
(TDPAC) of the cascade gamma rays.
The TDPAC spectra at four temperatures are
presented in Fig. 3-37. The anisotropy of the two
gamma rays is represented as R(t). Contrary to
the expectation of the oscillation due to the
electric quadrupole interaction between 111 In and
the extranuclear charge distribution, fast spectral
damping was observed at the respective
temperatures. The larger final isotropy at 673 K
implies the recombination and movement of
111
In in the materials. For further information,
measurements at higher temperatures are
necessary.
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93
Fig. 3-37. TDPAC spectra of 111 Cd
( 111 In) in HPOG at 673, 473, 373, 298
K, respectively.

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