S. T. Hsieh

NEGATIVE-PARITY STATES OF N = 88 ISOTONES IN THE INTERACTING BOSON APPROXIMATION

Abstract The negative-parity states of N =88 isotones are studied systematically in terms of the interacting boson approximation A mass-independent effective interacting boson hamiltonian reproduced energy levels very well. Unified E1 and E3 transition operators are found. The effect of p bosons on the energy spectra and electromagnetic transitions is discussed.

Non-normal parity states in A = 15, 14 and 13 nuclei

Abstract Shell-model calculations for the non-normal parity states of A = 15, 14 and 13 nuclei are carried out within the framework of the 1p n-1 (2s, 1d) and 1s 3 1p n+1 configurations where n = A − 4. The matrix elements of the two-body interactions between the 1p nucleons are fixed to be those determined by Cohen and Kurath from a least-squares fit. In addition, the two-body interactions between inequivalent nucleons are assumed to arise from a central force. The results for energy levels, transition probabilities and spectroscopic factors are in good agreement with experiment.

Effective-interaction calculation of the energy spectra of copper isotopes

SummaryEleven energy spectra of copper isotopes from58Cu to68Cu are studied in the conventional shell model. The model space is restricted to the low-seniority configurations. SomeT=0 two-body interactions are determined by a least-squares fit between the calculated and experimental low-lying energy levels. Good agreement is obtained with the observed level structure. Single-nucleon spectroscopic factors of64,66Cu are calculated and compared with experiments. The results show that the low-seniority restriction is an effective way to reduce the dimensionality of the model space for medium nuclei.RiassuntoSi studiano undici spettri di energia di isotopi di rame da58Cu a68Cu nel modello a strati convenzionale. Si restringe lo spazio modello alle configurazioni di seniorità inferiore. Alcune interazioni a due corpi conT=0 sono state determinate con un’approssimazione ai minimi quadrati fra i livelli d’energia inferiori calcolati e sperimentali. Si ottiene un buon accordo con la struttura dei livelli osservata. Si calcolano e si confrontano coi dati sperimentali i fattori spettroscopici di nucleone singolo di64,66Cu. I risultati mostrano che la limitazione alla seniorità inferiore è un metodo efficace per ridurre la dimensionalità dello spazio modello per nuclei medi.РеэюмеВ рамках стандартной оболочечной модели исследуются одиннадцать знергетических спектров иэотопов меди от58Cu до68Cu. Модельное пространство сводится к конфигурациям с малым синьоритетом. Испольэуя подгонку наименьщих квадратов между вычисленными и зкспериментальными ниэколежашими уровнями знергии, определяются некоторыеT=0 двухчастичные вэаимодействия. Получается хорощее согласие с обнаруженной структурой уровней. Вычисляются однонуклонные спектроскопические факторы иэотопов64,66Cu и сравниваются с реэультатами зкспе-риментов. Полученные реэультаты покаэывают, что ограничение, свяэанное с малым синьоритетом, представляет зффективный путь для уменьщения числа иэмерений модельного пространства для ядер вешества.

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.

Weak-coupling calculation on N = 83 isotones

SummaryA proton-neutron weak-coupling model calculation is performed on those N=83 isotones that are far fromZ = 50 proton closed shell. The agreement between the experimental and the calculated energy level schemes is quite good. The result suggests that the weak-coupling model proposed by McGrory is applicable not only to even-even nuclei, but also to even-odd and odd-odd nuclei.

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.

Study of Pt isotopes in the core excited interacting boson model 1

Abstract The core exited IBM model was applied to the Pt isotopes. It was found that the energy spectra of the high-spin states as well as those of the low-spin states can be reproduced quite well. Also, it was found that there is a structure transition between 186 Pt and 188 Pt. The B (E2) values of 184 Pt were calculated and compared with recent experimental data. It was found that the general features of the B (E2) values can be reproduced qualitatively. The need of more boson core excitations is also discussed.

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.