Nuclear spectroscopy of neutron-deficient La, Dy and Er activities

Abstract

A large accumulation of conversion-electron data has made it feasible to study the properties of nuclear levels in the rare-earth region of neutron numbers 88 to 94. The first experimental level scheme for 153Tb ( N = 88) is constructed; 84 transitions originate from 21 states excited below 1 MeV. The conversion spectrum of 155Tb is augmented from 40 to 120 transitions below 1.1 MeV energy. Multipole orders are deduced for 55 of the 96 transitions placed between 28 levels in 155Tb. Rotational parameters and γ-ray branching ratios are evaluated for 155Tb. Levels in the 0.5 to 1 MeV region are interpreted as β- and γ-vibrations of the 3 2 + [411] state, and a single-particle 1 2 + [411] band. Our data on 158Ho consists of 41 transitions, of which 30 are new, and almost all of the transition intensity is accounted for in the level spectrum. Neutron orbital 3 2 − [521] is found to be common to each of four low-lying intrinsic configurations in doubly odd 158Ho. The order of odd-proton orbitals coupled to 3 2 − [521] corresponds to that of single-particle states observed in neighboring 159Ho. Eighty conversion-electron transitions are observed below 1 MeV in 161Ho, a six-fold increase over preceding studies. Using photon intensities from independent research, multipole orders are deduced for most of the transitions de-exciting 18 nuclear levels in 161Ho. More evidence is presented on decay spectra of 131, 132mLa, including transition multipolarity assignments.