Hidekazu Kumagai

Neutron halo in 11Be studied via reaction cross sections

Abstract Reaction cross sections (σR) and fragmentation cross sections (σF) of reactions of a 11Be beam on C, Al targets were measured by a transmission method at 33A MeV. The σR have been determined to be 1.56±0.03 b for 11 Be + 12 C , and 2.27±0.05 b for 11 Be + 27 Al . These values are extremely large compared with the systematics of stable nuclei. A large σF has also been observed for the 11Be→10Be channel. Model calculations using present and 790A MeV data confirm the long neutron tail (neutron halo) in the 11Be density distribution.

Delay-line PPAC for high-energy light ions

Abstract We have developed a delay-line parallel-plate avalanche counter (PPAC) with high detection efficiency for high-energy light ions. A large signal-to-noise ratio was achieved by a newly designed pre-amplifier and the usage of C 3 F 8 gas at a pressure of 30 Torr . The counter has been tested with beams of 90 A MeV 7 Li at RIKEN, 340 A MeV 12 C at GSI, and 254 A MeV 8 B at GSI. We achieved high detection efficiencies (>95%) for all of these ions. Furthermore, we achieved reasonable position and timing resolutions.

Spectroscopy of 12Be and 13Be using a 12Be radioactive beam

Abstract We have studied 12 Be + p elastic and inelastic scattering and observed new levels of 12 Be at E 12 Be ∗ = 8.6, 10 and ∼ 14 MeV in the vicinity of He-emission thresholds, which can be candidates for states having an exotic cluster structure with He-like subsystems. Some new states were tentatively assigned to 13 Be in studies of the d( 12 Be, p) reaction.

Experimental study of 8He + p elastic and inelastic scattering

Abstract An experimental study of 8He + p elastic scattering and a search for 8He∗ as observed in two independent experimental methods. The obtained parameters of the excited state are E 8 He ∗ = 3.57±0.12 MeV , Γ =0.5±0.35 MeV, Γ 4 He+4n /Γ 6 He+n+n ⩽ 5% . Angular distributions for elastic and inelastic scattering are measured. The inelastic angular distribution is consistent with Jπ = 2+ for 8He3.55∗.

Measurements of 11Li+p and 9Li+p elastic scatterings at 60 MeV

Abstract Proton elastic scatterings of neutron rich nuclei 9 Li and 11 Li have been measured for the first time at E lab / A =60 and 62 MeV, respectively, under the inverse kinematical conditions. While the angular distribution of 9 Li scattering follows the systematic trend from those of 6 Li and 7 Li scatterings, the 11 Li cross section is smaller by about a factor of two. Optical model calculations show that considerable changes in both real and imaginary potentials are necessary to reproduce the 11 Li data.

High-spin isomer and level structure of 145Sm

Abstract High-spin states of 145 Sm were studied by using the reactions 20 Ne( 136 Xe,α7n), 16 O( 136 Xe,7n), 139 La( 10 B,4n) and 138 Ba( 13 C,6n). The level scheme was extended up to the state at 14.6 MeV. The excitation energy and the spin-parity of the 0.96 μs high-spin isomer were determined to be 8.8 MeV and ( 49 2 + ), respectively. Experimental results were discussed comparing with the deformed independent particle model calculation. High-spin isomers observed in N = 83 isotones were interpreted to be caused by the sudden shape change from near spherical to oblate. The Z = 64 shell gap energy was found to decrease from 2.4 to 2.0 MeV as the proton number decreases from Z = 64 to 61.

Positive and negative cluster ions and multiply charged ions produced from frozen nitrogen, carbon monoxide and oxygen molecules under energetic, heavy-ion impact

Abstract Positive and negative cluster ions have been observed in nitrogen, carbon monoxide and oxygen targets frozen at 15 K under 1.5 MeV u −1 Ar 13+ projectile ion impact. For positive cluster ions obtained from frozen nitrogen targets, even-number cluster series ions N + 2 n for n > 2 predominate over odd-number cluster series N + 2 n +1 . This is in sharp contrast to the fact that odd-number cluster series N − 2 n +1 are dominant in negative nitrogen cluster ions. Anions of N − 2 , etc., which do not exist in the gas phase, have been observed. Various positive cluster ions from frozen carbon monoxide targets have been observed, although pure carbon clusters C − n are dominant in the negative cluster ions. Clusters ions from frozen oxygen targets are formed with clustering element O 3 ; the O + 3 n +2 series are the dominant positive cluster ions, whereas the O − 3 n +3 series are much stronger than either O − 3 n +2 as regards the negative cluster ions. In addition multiply charged atomic ions have been observed from all the frozen targets investigated; these can be explained qualitatively as being due to Coloumbic explosion of multiply charged molecular ions originally produced in primary energetic ion collisions.

Experimental studies of light neutron rich nuclei

Abstract Experimental studies of neutron rich nuclei 8 He, 10 He, 12 Be and 13 Be have been performed using radioactive beams.

Coulomb excitation of 174Hf K-isomer. γ-ray spectroscopy with high-spin isomer beam

Abstract A new experimental technique utilizing a high-spin isomer beam (HSIB) has been developed. The HSIB of 174Hf was produced by the 9Be(170Er, 5n)174Hf reaction in inverse kinematics. By using the HSIB, the Coulomb excitation of the Kπ = 8− isomer in 174Hf was measured. The γ-rays from the 9− level, which is the first excited state built on the isomer, were observed as well as the cascade γ-rays of the ground-state rotational band. From the measured γ-ray yield, a value of 2 ± 1 e2b2 was extracted for the B(E2: 8− → 9−). This is the first experiment of γ-ray spectroscopy by means of the HSIB-induced secondary reactions.

Attempts in detection of neutrons on So-called cold nuclear fusion

Neutron emissions from electrolysis of D 2 O with palladium and palladium-titanium electrodes as well as from pressurized D 2 gas with titanium alloys have been measured. The neutron detector system was so designed to have very low background condition. Neutron-γ separation technique using liquid scintillator was applied to obtain essentially no γ ray background condition for neutron counting. Special care was taken to stabilize the detection system using event-by-event data recording. No significant signal of neutron emission was observed. Upper limits of emission probability of neutron have been determined to be 6×10 -3 s -1 , 1×10 -2 s -1 , and 2.3×10 -2 s -1 for Pd electrode, Pd-Ti electrode, and pressurized gas systems. These values are orders of magnitude lower than that presented by Jones paper (0.4 s -1 ).