Ikuko Hamamoto

Pseudospin in Rotating Nuclear Potentials

It is found that the concept of pseudo-spin and pseudo-oscillator quantum numbers, introduced by previous authors, can be helpful in understanding the qualitative features of quasiparticle motion in rotating potentials, for the orbits with normal parity (excluding the high j orbits). In the first part of the paper, the use of pseudo-spin in static deformed potentials is briefly reviewed.

Transition rates for a triaxial rotor plus a single quasi-particle

Abstract E2 and M1 matrix elements are considered for the system consisting of a triaxial rotor and a single quasiparticle. While B(M1) values are more closely related to the signature-splitting of the quasiparticle spectra, E2 matrix elements exhibit directly the information on the shape of the system.

Signature inversion at low spins of odd-odd nuclei: Triaxial shape?

Abstract It is shown that the signature inversion in the rotational spectra of the high- j -configuration bands, which has been observed at low spins of some odd-odd nuclei, can well be consistent with an axially symmetric shape. Thus, the observed signature inversion may not be taken as evidence for a triaxial shape.

On the intrinsic spectra of rotating nuclei with tri-axial shape

Abstract In connection with the analysis of a nuclear system with triaxial shapes, some features of the intrinsic excitation spectrum are discussed and especially interpreted in terms of the geometry of the classical orbits for configurations with a single large-j value. The “anomalous” signature for the lowest quasiparticle state appears as a particularly striking indicator for the occurrence of positive γ-values.

Effect of rotation on M1 and E2 transitions in odd-A nuclei

Abstract With the angular momentum as a good quantum number, a strong perturbation effect of rotation on M1 and E2 transitions is demonstrated. It is shown that calculated B ( M 1) values of a certain type of transitions almost vanish for a particular set of parameters. The B ( E 2) values of cascade transitions are found to be useful as a good test of wavefunctions.

NUCLEAR OCTUPOLE VIBRATIONS IN THE ISOTOPES OF Pb.

Abstract By using the particle-vibration coupling model the frequency and the oscillator strength of the octupole vibrations in the nuclei of the lead isotopes are evaluated and compared with experiments. It is shown that in the heavy even- A isotopes (i.e. 210 Pb, 212 Pb etc.) the oscillator strength of the lowest 3 − state (at 2.62 MeV) of 208 pb is divided approximately into two low-lying states. The quadrupole moment of 3 − state in 208 pb is also calculated by using the present model and compared with the recent measurement.

Strong selection-rules for M1 transitions in rotating nuclei

Abstract It is pointed out that even a small rotation has a drastic effect on M1 transition matrix elements between the nucleons in high- j orbits. The effect is in nice agreement with recent experimental observations. A simple model is used to clarify the results of numerical calculations.

Shell-structure and octupole instability in fermion systems

Simulating the one-particle spectra of the infinite-well potential by a model, we study the symmetry and the shell-structure of octupole deformations as well as the possible occurrence of octupole (and quadrupole) instabilities. Among various types of octupole deformations investigated theY32-type deformation is found to have a strong shell-structure as well as a very interesting symmetry which leads to the occurrence of highly-degenerate single-particle levels. One particle spectra of the octupole-coupled two-level model (withl andl + 3) are analytically studied in the limit of large angular-momentum,l.

Multiple band structure and band termination in 157Ho towards complete high-spin spectroscopy

Abstract Rotational bands of 157 Ho have been populated via the 124 Sn( 37 Cl, 4n) reaction at beam energies of 155 and 165 MeV. Gamma-ray spectroscopy was performed using the 8 π spectrometer at Chalk River. Many rotational bands have been observed for the first time. A detailed level scheme is presented, containing approximately 380 transitions, and the quasiparticle structure of the various bands is discussed. Band termination has been observed in the yrast states. For strongly coupled bands, B (M1)/ B (E2) transition strength ratios are extracted and compared with previous measurements and theoretical expectations. Branching ratios for out-of-band E2 transitions are analysed to extract band mixing interaction strengths. Implications for rotational damping are considered. The interaction at the first backbend in the ground band is found to be strongly signature dependent; this is evidence for a signature-dependent triaxial shape of the nucleus.

Electric-dipole transitions in deformed rare-earth nuclei

Abstract Both the absolute magnitude and the angular-momentum dependence of electric-dipole (E1) transition probabilities in quadrupole-deformed rare-earth nuclei are investigated in connection with the yrast spectroscopy. It is found that even in the most stable nuclei against octupole deformations the features of the measured E1-transition probabilities are not explained without invoking a coupling to octupole vibrations together with the E1 momentum carried by the octupole modes. The influence of octupole modes with both K π =0 − and 1 − on E1 transitions is discussed.