Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Thursday
HK45 Nuclear Physics / Spectroscopy VII
Time: Thursday 16:00–18:00 Room: B
Group Report HK 45.1 Thu 16:00 B
β-decay studies of exotic nuclei and states close to 100 Sn : 94 Ag
and 100 In — •C. Plettner for the GSI-ISOL collaboration — GSI,
Darmstadt, Germany
Nuclei along the N=Z line up to the doubly-magic 100 Sn have been
subject to extensive experimental studies both in β decay and in-beam
experiments. In various theoretical approaches the proton-neutron (πν)
interaction in identical orbits has been addressed, which gives rise to
a new S=1 pairing mode and, in stretched configurations, to spin-gap
isomers. The interplay of mean field (single-particle energies), residual
πν-interaction (empirical vs. realistic) and model space (core excitation)
will be demonstrated for two key examples: • 94 Ag is the heaviest N=Z
nucleus studied in detailed β-decay spectroscopy. It exhibits three β-
decay parent states, namely the T=1, I π =0 + , T1/2 =29± 29
10 ms ground
state [1], a T=0, I π =(7 + ), T1/2 =0.36 ± 3 s isomer and a T1/2 =0.3 ± 2
s, I > 15 high-spin isomer. The latter is suspect to establish records
both in spin (I π =21 + ) and excitation energy Ex > 6 MeV among the
known part of the Segré chart. • 100 In is the closest neighbour to 100 Sn
studied both in high-resolution and total absorption spectroscopy. Spin
I π =7 + and T1/2 =6.2 ± 4 s were determined for its ground state, which
is at variance with various shell model predictions.
[1] A. Stolz et al., Proc. PINGST 2000, Selected Topics on N=Z Nuclei,
eds. D. Rudolph, M. Hellström, Lund, Sweden, LUIP003, Bloms i Lund,
2000, p.113
Group Report HK 45.2 Thu 16:30 B
Shape coexistence in the Pb region — •kris heyde1 , ruben
fossion1 ,andjose-enrique garcia-ramos2 — 1Department of subatomic
and radiation physics, University of Gent, Proeftuinstraat,86 B-
9000 Gent (Belgium) — 2Departamento de Fisica Aplicada. EPSLa
Rabida, Universidad de Huelvam 21819 Palos de la Frontera, Spain
The Pb region has formed a most interesting testing region and in recent
experiments (in-beam work, beta-decay, alpha-decay,..) using stateof-the
art techniques, evidence has resulted for the coexistence of both
spherical, oblate and prolate structures. The data basis at present encompasses
both the region near the doubly-closed shell Z=82,N=126, the
neutron-deficient region spanning all the way down to neutron mid-shell
N=104 and also, presently, is bringing in results on the heaviest Pb nuclei
( beyond N=126).
Using both algebraic methods in which multi-particle multi-hole excitations
across the Z=82 shell are treated as extra pairs, as well as using
deformed mean-field calculations, a comprehensive set of results is obtained.
Thereby we accentuate both the symmetry aspects that govern
the interacting boson model algebraic structures as well as the shape
degrees of freedom that become active in these single-closed shell nuclei.
We shall higlight both the extensive data basis as well as the recent
theoretical results.
HK 45.3 Thu 17:00 B
Spin-Orientation in a projectile-fragmentation reaction —
•dana borremans1 , Gerda Neyens1 , Dimiter Balabanski1 ,
Nico Coulier1 , Jean-Michel Daugas1 , Francois de Oliveira2 ,
Georgi Georgiev1,2 , Marek Lewitowitz2 , Oscar Navilliat
Cuncic3 , Iolanda Matea2 , Mihai Stanoiu2 , Stephanie
Teughels1 , and Katrien Vyvey1 — 1Celestijnenlaan 200D,
3001Heverlee,Belgium — 2GANIL, Caen,France — 3LPC, Caen, France
To measure nuclear moments of short-lived nuclei, we need often an
initially oriented ensemble of nuclear spins. This orientation can be the
result of nuclear reactions. For the production of exotic nuclei, we use
a projectile-fragmentation reaction. It has been shown that nuclei produced
in such reaction are spin-oriented [1-4], but the spin orientation
mechanism is not yet completely understood. At GANIL we studied the
orientation in a projectile-fragmentation reaction using β-Level Mixing
techniques [5]. In this talk the idea behind the measurement of spinorientation
and the orientation mechanism will be explained, concluding
with some results.
[1] W.D.Schmidt-Ott et al., Z. Phys. A350 (1994) 215
[2] K.Asahi et al., Phys Lett. B 251 (1990) 488
[3] K.Asahi et al., Phys.Rev. C 43 (1991) 456
[4] G.Neyens et al., Phys.Lett. B393 (1997) 36
[5] G.Neyens et al., Phys. Res. A340 (1994) 555
*D.B.is an assistant researcher,G.N. a post-doctoral researcher of
FWO-Vlaanderen.
HK 45.4 Thu 17:15 B
γ-Spectroscopy of 40 Ca and 42 Ca — •S . Torilov 1 , S. Thummerer
1 , W. von Oertzen 1 , B. Gebauer 1 , H.G. Bohlen 1 , Tz.
Kokalova 1 , A. Tumino 1 , G. de Angelis 2 , M. Axiotis 2 , A.
Gadea 2 , E. Farnea 2 , N. Marginean 2 , T. Martinez 2 , D.R.
Napoli 2 , M. De Poli 2 , S.M. Lenzi 3 , C. Ur 3 , C. Beck 4 , M.
Rousseau 4 , and P. Papka 4 — 1 Hahn-Meitner-Institut Berlin —
2 INFN, Laboratori Nazionali di Legnaro — 3 Dipartimento di Fisica and
INFN, Padova — 4 Institut de Recherches Subatomiques
In the present work high-lying levels of two even isotopes of Ca were
studied using particle-γ coincidence. To select the reaction channels for
γ-spectroscopy the Si-ball ISIS has been used in combination with the
GASP γ-detector array at LNL Legnaro.
From this experiment 19 new levels and 25 new transitions for 40 Ca
for excitation energies up to 21 MeV and 5 new levels and 5 new transitions
for 42 Ca up to 13 MeV were found. The present data show in 40 Ca
clearly sperarated rotational bands with a 4p-4h and 8p-8h structure and
a mixture of different structures in the yrast line.
For 42 Ca some very good candidates were found for the 12 + state of
the 6p-4h band.
HK 45.5 Thu 17:30 B
Structure of excited K π =0 + bands in 168 Er. — •A. Linnemann
1 , J. Jolie 1 , H.G. Börner 2 , M. Jentschel 2 ,andP. Mutti 2
— 1 Institut für Kernphysik, Universität zu Köln — 2 Institut Laue-
Langevin,38042 Grenoble, France
In order to investigate the character of excited K π =0 + bands, that
can be interpreted as β- orγγ-bands, the knowledge of absolute decay
rates is mandatory. We have studied the second excited K π =0 + band
in 168 Er using neutron capture on 167 Er and the γ-ray-induced Dopplerboardening
technique (GRID) to measure the lifetimes. The experiment
was performed at the double-flat-crystal spectrometer GAMS4 installed
at the Laue-Langevin (ILL) in Grenoble. The lifetimes of the 2 + 4 state
at 1493 keV and the 4 + 4 state at 1656 keV could be measured for the
first time. The collectivity of this band can be studied using the absolute
transition rates.
HK 45.6 Thu 17:45 B
Bremsstrahlung emission in the α decay of 210 Po — •Hans Boie,
Jörg Fitting, Frank Köck, Martin Lauer, Heiko Scheit, and
Dirk Schwalm —MPIfür Kernphysik, Heidelberg
The emission of bremsstrahlung is usually well described by a semiclassical
treatment. However, in an α decay the α particle is tunneling
through the Coulomb barrier of the nucleus, a process which can only be
understood quantum-mechanically. The question that arises is: How is
the bremsstrahlung emission influenced by the tunneling process?
A typical emission probability of bremsstrahlung in the α decay
of 210 Po in the interesting Eγ region (∼400 keV) is about 10 −12
keV −1 decay −1 . Recent measurements [1] show that the simple Coulomb
acceleration model overestimates the data by more than an order of
magnitude. Several theoretical treatments of the problem have been
published (e.g. [2]). Due to poor statistics the data available so far does
not allow to distinguish between these models. In addition, the results
of [1] are in disagreement with a previous measurement.
To clarify the situation and to provide high statistics data an experiment
is presently being performed at the MPI-K Heidelberg, where the
bremsstrahlung γ rays and the coincident α particles are detected by a
cluster of three sixfold segmented HPGe detectors (of MINIBALL type
[3]) and two silicon strip detectors, respectively. The experimental setup
and preliminary results will be presented.
[1]J.Kasagiet.al.,Phys.Rev.Lett.79, 371 (1997).
[2] T. Papenbrock and G. F. Bertsch, Phys. Rev. Lett. 80, 4141 (1998).
[3] J. Eberth et. al., Prog. Part. Nucl. Phys. 46, 389 (2001).