NUCLEAR LEVEL STRUCTURES OF THE N=82 NUCLEI ERBIUM-150, THULIUM-151, AND YHERBIUM-152
Abstract
The level structures of the proton-rich N = 82 nuclei ('150)Er, ('151)Tm, and ('152)Yb, with 4,5, and 6 valence protons outside a ('146)Gd core, have been investigated. Self-supported 1 mg/cm('2) targets located inside a large NaI sum-spectrometer were bombarded with 225-255 MeV ('58,60)Ni beams, and recoiling residual nuclei were stopped in a ('208)Pb catcher foil 21 cm downstream, where detailed (gamma)-ray measurements were performed. The identification of (gamma)-rays associated with a particular residual nucleus was based on (a) coincidences with characteristic K x-rays, which determined the Z (b) coincident sum-spectra, excitation functions, and cross-bombardment results, which settled the A-assignment. In addition to the three N = 82 nuclei, (gamma)-ray families in the N = 83 nuclei ('151)Er and ('152)Tm and in the N= 81 nuclei ('147)Dy and ('149)Er, were also identified. Yrast levels up to 9509 kejV in ('150)Er have been established, with isomeric levels at 2797, 7372, and 9509 keV; in ('151)Tm and ('152)Yb, yrast levels up to 2655 and 2690 keV, respectively, have been established. The observed levels below 5.5 MeV in ('150)Er, and those in ('151)Tm and ('152)Yb, are interpreted in terms of (pi)h(,11/2)('n), (pi)h(,11/2)('n-1)s(,1/2), and (pi)h(,11/2)('n-1)d(,3/2) shell model configurations involving the n valence protons, and octupole excitations. The energies of (pi)h(,11/2)('n) states in these nuclei agree quite well with those calculated using empirical two-body interactions taken from the complete (pi)h(,11/2)('2) spectrum of ('148)Dy. The observed B(E2) values between (pi)h(,11/2)('n) states of seniority-two in ('148)Dy, ('150)Er, and ('152)Yb, and of seniority-three in ('149)Ho and ('151)Tm, are found to agree closely with theoretical values calculated using a single value of 1.52 e for the proton effective change. In this respect, their properties match shell model predictions even better than those of j('n) states near traditional doubly magic nuclei.
Degree
Ph.D.
Subject Area
Nuclear chemistry
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