Y. Ichikawa

Analyzing power for proton elastic scattering from the neutron-rich He6 nucleus

Vector analyzing power for the proton-{sup 6}He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target, which works at a low magnetic field of 0.09 T. The results are found to be incompatible with a t-matrix folding model prediction. Comparisons of the data with g-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The {alpha}-core distribution in {sup 6}He is suggested to be a possible key for understanding the nuclear structure sensitivity.

Lifetime measurements of first excited states in C 16 , 18

The electric quadrupole transition from the first 2{sup +} state to the ground 0{sup +} state in {sup 18}C was studied through a lifetime measurement by an upgraded recoil shadow method applied to inelastically scattered radioactive {sup 18}C nuclei. The measured mean lifetime is 18.9{+-}0.9(stat){+-}4.4(syst) ps, corresponding to a B(E2;2{sub 1}{sup +}{yields}0{sub g.s.}{sup +}) value of 4.3{+-}0.2{+-}1.0 e{sup 2} fm{sup 4}, or about 1.5 Weisskopf units. The mean lifetime of the first 2{sup +} state in {sup 16}C was remeasured to be 18.3{+-}1.4{+-}4.8 ps, about four times shorter than the value reported previously. The discrepancy between the two results was explained by incorporating the {gamma}-ray angular distribution measured in this work into the previous measurement. These transition strengths are hindered compared to the empirical transition strengths, indicating that the anomalous hindrance observed in {sup 16}C persists in {sup 18}C.

Proton-rich nuclear structure and mirror asymmetry investigated by β-decay spectroscopy of 24Si

In order to investigate the characteristic properties of proton-rich nuclei, β-decay spectroscopy was carried out on 24Si. The Gamow-Teller transition strength B(GT) of 24Si to low-lying states in 24Al was determined. Considering in particular the breaking of mirror symmetry for energy levels and B(GT), we discuss the behavior of a weakly-bound s-orbital proton by incorporating a recent experimental result.

Elastic Scattering of Neutron-Rich Helium Isotopes from Polarized Protons at 71 MeV/A

The vector analyzing power has been measured for the elastic scattering of neutron-rich 6He and 8He from polarized protons at 71 MeV/A making use of a newly constructed solid polarized proton target operated in a low magnetic field of 0.1 T and at a relatively high temperature of 100 K. An optical model analysis revealed that the spin-orbit potentials for 6He and 8He are characterized by shallow and long-ranged shape compared with the global systematics of stable nuclei. Such a characteristics reflect a diffused density distribution of the neutron-rich isotopes.

{beta} decay of the proton-rich nucleus {sup 24}Si and its mirror asymmetry

{beta}-decay spectroscopy of the proton-rich nucleus {sup 24}Si was performed. The decay scheme was reconstructed from results of delayed {gamma}-ray and proton measurements. We observed two {beta} branches to bound states in {sup 24}Al for the first time. The branching ratios were determined to be 31(4)% and 23.9(15)% for the 1{sub 1}{sup +} state at 0.426 MeV and the state at 1.090 MeV, respectively. The observation of an allowed transition to the 1.090-MeV state enabled us to firmly determine its spin-parity as 1{sup +}. In the proton measurements performed with the {delta}E-E method, we observed a new unbound level at 6.735 MeV. The branching ratios to three unbound states, including the new level, were also determined for the first time. Based on the decay scheme, the B(GT) values of {sup 24}Si were deduced. The B(GT) values were smaller than those of the mirror nucleus {sup 24}Ne by 22% and 10% for the 1{sub 1}{sup +} and 1{sub 2}{sup +} states, respectively. The mirror asymmetries of B(GT), observed in both the 1{sub 1}{sup +} and the 1{sub 2}{sup +} states, indicate changes in configuration in the wave function associated with the Thomas-Ehrman shift. To clarify the mechanism of this asymmetry, amorexa0» comparison with shell-model calculations is also discussed. The calculations attribute the changes in configuration to the lowering of the 1s{sub 1/2} orbital.«xa0less

Investigation into behavior of weakly-bound proton via B(GT) measurement for the β decay of 24Si

The β‐decay spectroscopy on 24Si was carried out in order to investigate the behavior of a weakly‐bound s‐wave proton. We observed two β transitions to low‐lying bound states in 24Al for the first time. The Gamow‐Teller transition strengths B(GT) to the 11+ and 12+ states were deduced to be 0.13(2) and 0.14(1), which were smaller than that of mirror nucleus 24Ne by 22% and 10%, respectively. These mirror asymmetries of B(GT) indicate the configuration change in the wave function. By comparing with theoretical shell‐model calculations, it is implied that the configuration change is attributed to the lowering of the 1s1/2 orbital.

ANOMALOUSLY HINDERED E2 STRENGTHS IN 16,18C

Lifetime measurement of the first excited 2+ state in 18C was performed using an upgraded recoil shadow method to determine the electric quadrupole transition. The measured mean lifetime is 18.9 ± 0.9 (stat) ± 4.4 (syst) ps, which corresponds to a value of 4.3 ± 0.2 ± 1.0 e2fm4, or about 1.5 Weisskopf units. The mean lifetime of the first 2+ state in 16C was remeasured to be about 18 ps, about four times shorter than the value reported previously. By incorporating the γ-ray angular distribution measured in this work into the previous measurement, this discrepancy has been explained. The observed transition strengths in 16,18C are hindered compared to the empirical transition strengths, indicating that the anomalous hindered E2 strength observed in 16C persists in 18C.

Analyzing Power Measurement for Elastic Scattering of 6He on Polarized Protons

Vector analyzing power was measured for the proton elastic scattering on 6He at 71 MeV/u. We applied a solid polarized proton target, which was operated in a low magnetic field of 88 mT and at high temperature of 100 K, to a radioactive‐isotope beam experiment. Low energy recoil protons were successfully detected due to the modest operation conditions of the target. Selection of p+6He elastic scattering events was clearly carried out with detected protons. Absolute values of the analyzing power were determined for the first time.

Spectroscopy on neutron-rich nuclei near N = 50 via two-step Coulomb excitation at intermediate energies

We have investigated structure of the neutron-rich Ge isotopes at and around N = 50 via intermediate-energy Coulomb excitation. A new method of intermediate-energy twostep Coulomb excitation has been tested to study the second excited states, such as the 2+2 and 4+1states, in neutron-rich even-even nuclei. The first application of the method and its results are presented.

6He scattering with polarized proton target

A new type of the spin polarized solid proton target has been constructed which can be operated under a low magnetic field of 0.08 T and a high temperature of 100 K. First polarization asymmetry measurement with an unstable beam of 6He with an energy of 71 MeV/u has been successfully carried out.