Yoshifumi R. Shimizu

Determination of the structure of {31}ne by a fully microscopic framework.

We perform the first quantitative analysis of the reaction cross sections of {28-32}Ne by {12}C at 240  MeV/nucleon, using the double-folding model with the Melbourne g matrix and the deformed projectile density calculated by antisymmetrized molecular dynamics. To describe the tail of the last neutron of {31}Ne, we adopt the resonating group method combined with antisymmetrized molecular dynamics. The theoretical prediction excellently reproduces the measured cross sections of {28-32}Ne with no adjustable parameters. The ground state properties of {31}Ne, i.e., strong deformation and a halo structure with spin parity 3/2{-}, are clarified.

γ-tunneling calculations for the decays of the K isomers in the Hf, W, Os region

Abstract Recent studies of the high- K isomers in the Hf, W, Os region have uncovered the existence of direct branches to the low- K rotational bands with unexpectedly large transition probabilites. The measured hindrance factors have called the validity of the K quantum number into question. In order to give a new insight to this problem, we have performed systematic calculations of the M1 and E2 partial life times of the K isomers by using a simple tunneling model in which the γ degree of freedom is taken into account. Many of the observed partial life times are reproduced by the model, but some data remain completely off the calculations. This requires further studies of the spin-orientation degree of freedom.

Determination of the Structure ofNe31by a Fully Microscopic Framework

We perform the first quantitative analysis of the reaction cross sections of {28-32}Ne by {12}C at 240  MeV/nucleon, using the double-folding model with the Melbourne g matrix and the deformed projectile density calculated by antisymmetrized molecular dynamics. To describe the tail of the last neutron of {31}Ne, we adopt the resonating group method combined with antisymmetrized molecular dynamics. The theoretical prediction excellently reproduces the measured cross sections of {28-32}Ne with no adjustable parameters. The ground state properties of {31}Ne, i.e., strong deformation and a halo structure with spin parity 3/2{-}, are clarified.

Microscopic structure of high-spin vibrational excitations in superdeformed {sup 190,192,194}Hg

Microscopic calculations based on the cranked shell model extended by the random-phase-approximation are performed to investigate the quadrupole and octupole correlations for excited superdeformed bands in {sup 190}Hg, {sup 192}Hg, and {sup 194}Hg. The {ital K}=2 octupole vibrations are predicted to be the lowest excitation modes at zero rotational frequency. At finite frequency, however, the interplay between rotation and vibrations produces different effects depending on neutron number: The lowest octupole phonon is rotationally aligned in {sup 190}Hg, is crossed by the aligned two-quasiparticle bands in {sup 192}Hg, and retains the {ital K}=2 octupole vibrational character up to the highest frequency in {sup 194}Hg. The {gamma} vibrations are predicted to be higher in energy and less collective than the octupole vibrations. From a comparison with the experimental dynamic moments of inertia, a new interpretation of the observed excited bands invoking the {ital K}=2 octupole vibrations is proposed, which suggests those octupole vibrations may be prevalent in superdeformed Hg nuclei. {copyright} {ital 1996 The American Physical Society.}

Deformation of Ne isotopes in the region of the island of inversion

The deformation of Ne isotopes in the island-of-inversion region is determined by the doublefolding model with the Melbourne g-matrix and the density calculated by the antisymmetrized molecular dynamics (AMD). The double-folding model reproduces, with no adjustable parameter, the measured reaction cross sections for the scattering of Ne from C at 240MeV/nucleon. The quadrupole deformation thus determined is around 0.4 in the island-of-inversion region and Ne is a halo nuclei with large deformation. We propose the Woods-Saxon model with a suitably chosen parameterization set and the deformation given by the AMD calculation as a convenient way of simulating the density calculated directly by the AMD. The deformed Woods-Saxon model provides the density with the proper asymptotic form. The pairing effect is investigated, and the importance of the angular momentum projection for obtaining the large deformation in the island-of-inversion region is pointed out.

Rotational bands in 238U

Abstract A thick foil of 238 U was bombarded with 209 Bi beams at 1130 and 1330 MeV, delivered by the TASCC facility at Chalk River Laboratories. Gamma-ray spectroscopy of states populated in multiple Coulomb excitation was performed with the 8π spectrometer, an instrument comprising 20 Compton-suppressed HPGe detectors and 71 BGO ball elements. The event trigger required that 3 BGO elements and 2 HPGe detectors fire in coincidence. The experiment achieved a high degree of sensitivity, the weakest rotational band observed had about 0.16% intensity of the ground state rotational band. Several bands were observed to high spin for the first time, including the γ-vibrational band (spin 27 + ) and the octupole bands with K = 0 (spin 31 − ), K = 1 (spin 28 − ) and K = 2 (spin 25 − ). Results for positive and negative parity vibrational bands are compared with cranked RPA calculations. Although this theory can explain some features of the data, many puzzling aspects remain to be explored.

Effects of pairing correlations on superdeformed bands in the A ≈ 150 region

Abstract A systematic investigation of the J( 1 ) and J( 2 ) moments of inertia for superdeformed bands in the mass A ≈ 150 region has been carried out. Satisfactory overall agreement with experimental data is obtained by taking pair correlations into account supplementing the standard cranked Nilsson-Strutinsky model with calculations performed within the cranked BCS plus RPA approach.

Ground-state properties of neutron-rich Mg isotopes

We analyze recently measured total reaction cross sections for

Wobbling motion in atomic nuclei with positive gamma shapes

{}^{24--38}

Deformation Effect on Total Reaction Cross Sections for Neutron-Rich Ne-Isotopes

Mg isotopes incident on