M. M. King Yen

IBA calculations on the even-even Pt isotopes

Abstract By performing least-squares-fit calculations on the energy spectra of the even-even 186–196 Pt isotopes, the IBA model I and the IBA model II are compared on an equal footing. It is found that both model I and model II can fit energy spectra and absolute B (E2) transition rates reasonably well. Model II shows a distinct improvement in the energy spectra of β-bands of heavier nuclei in the isotope series. It is suggested that for regions far from the closed shells model I may be used to simulate model II as a useful phenomenological probing tool.

Shell-model studies of the 90Y, 91Zr, 92Nb and 93Mo nuclei☆

Abstract A shell-model calculation of the N = 51, 39 ≦ Z ≦ 42 nuclei is presented. The 88 Sr nucleus is assumed to be an inert closed core. The extra-core protons are restricted to the ( 2 p 1 2 , 1 g 9 2 ) configurations, and the active neutron is allowed to occupy the 2 d 5 2 , 3 s 1 2 , 2 d 3 2 and 1 g 7 2 orbits. The proton-proton effective interaction is directly taken from the previous analysis on the energy levels for N = 50 isotones by Ball et al . The proton-neutron effective interaction is assumed to be of the form of the surface δ-interaction. The energy spectra are calculated from a least-squares fit to the experimental data, varying the T = 0 and T = 1 strengths of the surface δ-interaction. Spectroscopic factors, E2 transition rates and two-body matrix elements are also calculated and compared with the observed values and the previous theoretical results.

Shell-model studies of negative-parity states in nuclei with A=18, 19 and 20

A shell-model calculation of the negative-parity states in the A=18, 19 and 20 nuclei is presented. Assuming the nucleus 16O to be the core, an active hole is restricted to the 1p1/2 or 1p3/2 orbits, and active particles are allowed to occupy the 1d5/2 and 2s1/2 orbits. The two-body effective interaction is assumed to be a central potential which has Yukawa radial dependence. The energy spectra are calculated from a least-squares fit to the experimental data, varying the strengths of the exchange interaction and the single-particle level splittings. Spectroscopic factors and E2, E3 and M1 transition rates are calculated and compared with the observed values.

A three-band interpretation of the high-spin states in even 172-180Os isotopes

An IBA plus two-quasiparticle calculation has been carried out systematically for the light even osmium isotopes with mass numbers between 172 and 180. Single-particle orbits i13/2 and h9 are considered. The differences and similarities of the yrast spectra have been reflected properly in both the interaction parameters and level wavefunctions obtained.

Effective boson calculations on Sm isotopes

Effective boson numbers are introduced in IBA-1 calculations to simulate the partial subshell closure effects at Z=64. The energy levels, wavefunctions and B(E2) values of Sm isotopes are calculated and compared with the experimental data. It is found that the agreement with the experimental data can be improved by introducing effective boson numbers in the calculations.

Anomalies of moment of inertia in 170-180Os

The anomalies of the moment of inertia in 170-180Os are analysed in the interacting-boson-plus-fermion-pair model. The angular momentum-angular momentum interaction term (L.L) in the boson Hamiltonian is renormalized by a (1+fL.L)-1 factor. It was found that the renormalization facilitates the interaction parameter searching and all boson-boson and boson-fermion interaction parameters for the isotope chain can be unified. Energy levels can be reproduced quite well. The general features in the moment of inertia anomalies can be reproduced. The transition quadrupole moments are calculated and compared with other estimates.

Study of even-odd N=90 isotones in the IBA-plus-three-fermion model

The even-odd N=90 isotones are studied in the IBA-plus L three-fermion model. It was found that the signature dependence of the energy levels can be reproduced quite well for the levels below the second backbends. The backbending plots of the even-odd isotones show similar features to those of the adjacent even-even isotones. The calculated B(E2) values indicate sudden drops at the band crossing positions.

Calculations on the 1bar hω spectra for the nuclei 18O and 18F

A shell-model calculation including the complete 1p, 2s, 1d, 2p and 1f shells was performed for the non-normal parity states of the nuclei 18O and 18F. The basis is confined to 1h(cross) omega excitations. The nucleus 16O is assumed to be the core. The spurious states have been eliminated. The two-body effective interactions were chosen from previous works. Spectroscopic factors and EM transition rates were also calculated and compared with the observed values.

Weak-coupling calculation for high-spin neutron hole excitations in odd-A lead isotopes

A least-squares fit calculation has been performed on the low-lying spectra of 206,204,202,200,198Pb in a restricted neutron model space. The best-fit two-body interactions were then employed in a weak-coupling calculation to obtain the high-spin states in 203,201,199,197,195Pb considering hole-core coupling. Experimental single-particle energies and excitation energies of the core states were used. Although some difficulties showed up in fitting the even-mass spectra, the weak-coupling structures expected from data were reproduced reasonably well.

Effective interaction and energy spectra in the vicinity of 208Pb

Using a central-plus-tensor potential, the effective interactions are determined using the low-lying energy spectra of the nuclei in the vicinity of 208Pb. The effect of the second range of the potential is examined and the universal property of the potential is explored. It is found that it is possible to reproduce the energy spectra and manifest the universal features simultaneously. From the results of fittings the inclusion of the second range is favoured.