H. Utsunomiya

Strongly-suppressed post-Coulomb acceleration in non-resonant breakup of 7Li

Abstract Cross sections were measured at energies of astrophysical relevance for the non-resonant breakup of 42 MeV– 7 Li by 6 targets. It was found that post-acceleration of the α and the triton in the target Coulomb field is vanishingly small, independent of the target nucleus, compared to that for prompt breakup. The transition probabilities were evaluated for the astrophysical continua in 7 Li which decay by tunneling through the Coulomb barrier. They are consistent with the present observations.

Reaction mechanism of 6Li scattering at 600 MeV

Abstract: Elastic scattering and inclusive breakup of 6Li particles on 12C, 58Ni, 90Zr, and 208Pb targets are measured at 100A MeV. The elastic scattering data are compared with single channel and Coupled Discretized Continuum Channels calculations. The coupling-effect between the elastic and the breakup channels is important even at an incident energy of 100A MeV and cannot be neglected. The inclusive breakup data are investigated for orbital dispersion effects which are found to be less significant at 100A MeV. The longitudinal momentum distributions are broader than predicted by theoretical expectations.

Relation between the 16O(α, γ)20Ne reaction and its reverse 20Ne(γ, α)16O reaction in stars and in the laboratory

Abstract.The astrophysical reaction rates of the 16O (α,γ) 20Ne capture reaction and its inverse 20Ne (γ,α) 16O photodisintegration reaction are given by the sum of several narrow resonances and a small direct capture contribution at low temperatures. Although the thermal population of low-lying excited states in 16O and 20Ne is extremely small, the first excited state in 20Ne plays a non-negligible role for the photodisintegration rate. Consequences for experiments with so-called quasi-thermal photon energy distributions are discussed.

Excitation of continuum states in 7Li and their decay by quantum tunneling

Strong forward-backward asymmetries were found in the recent α — t coincidence measurement of Coulomb breakup of 42 MeV- 7 Li via continuum states. The competition between E1 and E2 multipolarities and higher order effects in Coulomb excitation were investigated by solving the time-dependent Schrodinger equation. It is shown that higher order effects are an essential ingredient to the observed large asymmetries. The relevant reaction mechanism is discussed.

Breakup of 30 MeV/u-16O in nuclear and Coulomb fields of 120Sn and 208Pb Nuclei

Abstract Coincidence measurements of α- 12 C pairs collinearly emitted in the breakup of 30 MeV/u- 16 O incident on 208 Pb and 120 Sn were performed with a two detector system set up along the focal plane of a magnetic spectrograph. Double differential cross sections for sequential breakup via the 2 2 + and 2 3 + states in 16 O were analyzed within the framework of coupled-channels (CC) calculations which incorporated microscopic α- 12 C cluster model wave functions for bound and unbound states of 16 O. The experimental data are satisfactorily reproduced by the CC calculations to within a factor of two. The results are discussed in terms of the interference between nuclear- and Coulomb-breakup amplitudes.

Trinucleon cluster structure at high-excitation energies in A=6 nuclei

Trinucleon molecular structures in 6He and 6Be were investigated by using the 6Li(7Li, 7Be)6He reaction at 455 MeV and 6Li(3He, t)6Be reaction at 450 MeV, respectively. Binary decays into t + t from a broad state at Ex=18.0±1.0 MeV in 6He and into 3He + 3He from one at Ex=18.0±1.2 MeV in 6Be, respectively, were observed by measuring trinucleon cluster decays in coincidence with reaction particles. The branching ratios for binary decay were estimated to be about 0.7 for 6He and 6Be. These large branching ratios show that a trinucleon cluster state exists as an isobaric partner around Ex=18 MeV in 6He and 6Be.

Pygmy dipole resonance and dipole polarizability in 90Zr

Electric dipole (E1) reduced transition probability B(E1) of 90Zr was obtained by the inelastic proton scattering near 0 degrees using a 295 MeV proton beam and multipole decomposition analysis of the angular distribution by the distorted-wave Born approximation with the Hartree-Fock plus random-phase approximation model and inclusion of El Coulomb excitation, and the E1 strength of the pygmy dipole resonance was found in the vicinity of the neutron threshold in the low-energy tail of the giant dipole resonance. Using the data, we plan to determine the precise dipole polarizability αD which is defined as an inversely energy-weighted sum value of the elecrric dipole strength. The dipole polarizability is expected to constrain the symmetry energy term of the neutron matter equation of state. Thus systematical measurement of the dipole polarizability is important.

Determination of photoneutron cross sections for [sup 197]Au by using laser inverse-Compton scattering gamma-rays

We measured photoneutron cross sections for 197Au with quasi‐monochromatic laser inverse‐Compton scattering gamma rays. We present results of the measurement in comparison with the existing data.We measured photoneutron cross sections for 197Au with quasi‐monochromatic laser inverse‐Compton scattering gamma rays. We present results of the measurement in comparison with the existing data.

Threshold photoneutron cross sections for {sup 208,207,206}Pb isotopes

Photoneutron cross sections for three Pb isotopes (206Pb, 207Pb, 208Pb) near neutron threshold were measured with the laser inverse‐Compton scattering gamma rays at the National Institute of Advanced Industrial Science and Technology. The cross section data are presented.

M1 and E1 transition cross sections in D(y→,n) reactions near reaction threshold

M1 and E1 transition cross sections in the D(y→, n) reaction were separately determined by measuring the analyzing power for emitted neutrons with linearly‐polarized γ rays at four energies between 2.26 MeV and 3.70 MeV near reaction threshold at 2.224 MeV. We compared the experimental result with the JENDL evaluated data.