T. Shimoda

Measurement of interaction cross sections using isotope beams of Be and B and isospin dependence of the nuclear radii

Abstract Interaction radii for 11,12,14 Be and 8,12,13,14,15 B have been determined by the measurement of interaction cross sections at 790 MeV/nucleon. Effective root-mean-square (RMS) radii of nucleon distribution of these nuclei have been deduced using a Glauber-model calculation. Isospin dependence of nuclear radii are presented for isobars of mass numbers from 6 to 12, and compared with theoretical predictions by the droplet model and by a Hartree-Fock (HF) model. The HF model with the Skyrme-III potential, which includes a strong density-dependent force, reproduce the observed isospin dependence.

Systematic behavior of ejectile spin polarization in the projectile fragmentation reaction

Abstract Ejectile spin polarization P in intermediate-energy projectile fragmentation has been measured for different targets and incident energies using the RIPS fragment separator at RIKEN. The observed P as a function of the fragment momentum shows a systematic change when the atomic number of the target or the incident energy is varied. Most remarkably, P does not vanish at the momentum corresponding to the beam velocity, indicating an important effect which has not been considered in the previously proposed model.

Spin-flip probability in heavy-ion inelastic scattering☆

Abstract The spin-flip probability S(θ) was observed in the reactions 12C(13C, 13C′)12C(2+1) and 12C(15N, 15N′)12C(2+1) at E( 13 C ) = 87 and E( 15 N ) = 94 MeV , respectively, by particle-gamma angular correlations, in which gamma rays emitted both in-plane and out-of-plane were detected. Distorted-wave Born-approximation (DWBA) calculations required a strength of 2–3 MeV for the spin-orbit interaction to reproduce the observed S(θ), which is significantly larger than that given by the folding-model description.

Direct measurements of (α, n) and (p, n) reaction cross sections using light neutron-rich radioactive nuclear beams

Abstract A project to acquire directly nuclear cross sections of (α, n) and (p, n) reactions using low energy light neutron-rich radioactive nuclear beams (RNB) is in progress at JAERI-Tandem facility. The method of the production of neutron-rich RNB, an improvement of a gas counter (MSTPC) in order to work effectively under the high RNB-injection rate, and the feasibility of our experiments are discussed.

Measurement of the 16N(α, n) reaction cross section

Abstract In order to study the starting point of the r-process, the 16 N(α, n) cross section has been measured directly at the energy region of E cm = 1.5 – 4.0 MeV, corresponding to the Gamow peak energy T 9 = 2 – 6.

Projectile-Breakup Process in 20Ne+40Ca Reactions at 92, 149 and 213 MeV

Alpha– 16 O correlation measurements have been performed to investigate whether the projectile breakup process takes place sequentially or directly in the 20 Ne+ 40 Ca reaction at 92, 149 and 213 MeV. For the three-body final channel α+ 16 O(g.s.)+ 40 Ca(g.s.) (elastic breakup channel), which has much larger cross section than the other channels, the coincidence events have been analyzed. By examining carefully the relative energy spectra between α and 16 O, it was found that the sequential breakup process via the excited states of 20 Ne at 5.78 (J π = 1, K π = 0), 6.72 (0 + , 0 2 + ), 7.17 (3 - , 0 - ), 8.78 (6 + , 0 1 - ), 10.26 (5 - , 0 - ) and 11.95 (8 + , 0 1 + ) MeV was dominant at the all incident energies. The direct breakup process which proceeds without any concern with the excited states of 20 Ne has not been observed with the sensitivity of the present measurement.

A Systematic Study of Astrophysical Reaction Rates through 8Li

Excitation functions of 8Li(α,n), (d, t) and 12B(α,n) reactions were directly measured in the energy region of astrophysical interest using low‐energy radioactive nuclear beams of 8Li and 12B. Each measured excitation function is strongly affected by one or more resonances through a compound nucleus. The measured excitation functions are presented. Dominant r‐process paths through 8Li at various temperatures are discussed and our future experimental plan is also presented.

A New Measurement of the 8Li(α,n)11B Reaction for Astrophysical Interest

The 8Li(α,n)11B reaction has been measured directly and exclusively in the energy region of Ecm=0.45–1.75 MeV by using highly efficient detector system covering Ecm= 0.56 MeV, which corresponds to the Gamow window at T9=1. This experiment has been performed in the condition of inverse kinematics by using low‐energy radioactive 8Li beam at the Tandem accelerator facility of Japan Atomic Energy Research Institute. The reaction cross section obtained in the present measurement is consistent with that of the previous exclusive measurements within the errors in an overlapping energy region, but is less than half of that of the inclusive measurements, in particular for lower energy region.

Study of astrophysical (α, n) reactions using light‐neutron rich radioactive nuclear beams

A systematic study of astrophysical reaction rates of (α, n) reactions on light neutron‐rich nuclei using low‐energy radioactive nuclear beams is in progress at the tandem facility of Japan Atomic Energy Agency. Exclusive measurements of 8Li(α, n)11B and 12B(α, n)15N reaction cross sections have been performed successfully. Their excitation functions together with the experimental method are presented.

Spin-polarized radioactive beams and β-NMR experiments

We discuss a new method of producing spin-polarized radioactive nuclear probes which capitalizes characteristic features of projectile fragmentation reaction at intermediate energies. Experimental results are given for the behavior of polarization as a function of the fragment momentum, target mass number, and beam energy. As an application of this method, we also report on results ofg-factor measurements for several neutron-rich nuclei. A full account of theg-factor measurement will be presented elsewhere.