Proton States in 155Tb, 157Tb, 159Tb, and 161Tb

Abstract

Proton states in the odd terbium isotopes 155Tb, 157Tb, 159Tb, and 161Tb have been studied using (3He,d) and (α,t) reactions. The beams of 24 MeV 3He and 25 MeV alpha particles were produced by the McMaster University model FN tandem Van de Graaff accelerator. The reaction products were analyzed with an Enge split-pole magnetic spectrograph and detected with photographic emulsions. The ratios of cross sections in the (3He,d) and (α,t) reactions were used as an indication of the/values for the proton transfers, and the spectroscopic factors were extracted using DWBA calculations. The results of the present work confirm the assignments of the 3/2+ [411] and 5/2+[413] Nilsson orbitals in all four isotopes. The I = 11/2 states of the 5/2−[532] and 7/2−[523] orbitals were identified in 161Tb and 159Tb and their assignments confirmed in 157Tb and 155Tb. It was necessary to invoke appreciable Coriolis mixing between these two orbitals in order to describe the observed rotational level spacings and the spectroscopic strengths. The assignments of the 7/2+[404] orbital were confirmed in 155Tb and 157Tb and this orbital was identified in 159Tb and 161Tb. Previous assignments of the 1/2+ [411] particle state with vibrational admixtures were confirmed in 157Tb and 159Tb and the state was identified in 161Tb. The present results support earlier evidence for the existence of a second fragment of the 1/2+[411] orbital in 159Tb and suggest the presence of a similar state in 157Tb. In each of the isotopes the 5/2+[402] orbital was assigned and a tentative assignment for the 1/2−[541] orbital was proposed.