OMEGAP = OMEGAN = 1/2 EXCITATIONS IN ODD NUCLEUS 172TM

The decay of 50 h 172Er has been investigated by electron and gamma-ray spectrometry and coincidence techniques. Excited levels, characterized by the quantum numbers (K, Iπ), have been established at the following energies in keV: 61(2, 3−), 407(1, 1−), 446(1, 2−), 475(0, 0−), 535(0, 1−) and 610(1, 1+).

The levels can be interpreted in terms of the Nilsson orbitals expected in this region. Thus the four states from 407 to 535 keV are taken to belong to the configuration p12+[411]±n12−[521], which gives rise to bands with K = 0 and K = 1. These two bands have an anomalous structure, partly because of the even-odd splitting in the K = 0 band, partly because of the Coriolis coupling between the two bands.

By an analysis of the beta-transition probabilities in the decay of 172Er and of 170Tm it is shown that the Coriolis coupling vanishes in the odd-spin states in agreement with expectations. However, an analysis based on the level spacings in 170Tm and 172Tm indicates that the appreciable rotational perturbations of the even-spin states deviate from the theoretical value.