TRIAC Progress Report - KEK

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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 <strong>TRIAC</strong> 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
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TRIAC Progress Report TRIAC collabo
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i KEK Progress Report 2011-1 June 2
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PREFACE The Tokai Radioactive Ion A
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1. Introduction Following the succe
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maximum available beam power for th
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container of ion source and uranyl
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gaseous and volatile elements (e.g.
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= 10.6 m) were 4.5 %, that for 146
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with different plasma volumes [2-6]
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ECR plasma: We used natural helium
Page 21 and 22: higher efficiency for gaseous eleme
Page 23 and 24: The asymmetric component representi
Page 25 and 26: ut differs from the electron-loss p
Page 27 and 28: consumption in the cavity is less t
Page 29 and 30: measured with Faraday cups, FC1, FC
Page 31 and 32: y turning off the supply of RF powe
Page 33 and 34: Encouraged by the new finding, as t
Page 35: 2-4-4. Development of superconducti
Page 40 and 41: accelerating the radioactive ion be
Page 42 and 43: Fig. 2-29. Photos of the pre-bunche
Page 44 and 45: For the proposed experiment, the po
Page 46: a diagonal direction. The monitors
Page 49: charge state of xenon ions by using
Page 52 and 53: electrode as shown in Fig. 2-40) sh
Page 54 and 55: CO2 (10 %) and 16 kPa, respectively
Page 56 and 57: Although the gain shift of THGEM#3
Page 58 and 59: 3. Experiments at the TRIAC Since t
Page 60 and 61: Fig. 3-1. Schematic view of the det
Page 62 and 63: -element abundances up to the third
Page 64: higher reliability of the experimen
Page 67 and 68: GEM-MSTPC among the accumulated dat
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Page 78 and 79: the observed CP-violating phenomena
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Page 82 and 83: Secondary 9 Li ions extracted from
Page 84 and 85: Fig.3-24. γ ray energy spectra coi
Page 86 and 87: In the experiments of RNB-J02/03 (S
Page 88 and 89: atio), a diffusion coefficient was
Page 91 and 92: Although the data for β-LiAl and
Page 93 and 94: In the experiment of RNB-K06 ((Spok
Page 95 and 96: difference spectra, more specifical
Page 97 and 98: Mass, which is one of the most fund
Page 99: gamma rays. 111 In, which decays to
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TRIAC Progress Report - KEK

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