A new assignment for the 9/2+[624] state in 181Hf from the 179Hf(t, p)181Hf reaction

Abstract

Angular distributions of protons from the 179Hf(t, p)181Hf reaction were studied using 15-MeV tritons from the McMaster University tandem Van de Graaff accelerator. The reaction products were analyzed with a magnetic spectrograph and detected with nuclear emulsions. Since the 179Hf target ground state is the 9/2+[624] orbital, a strong L = 0 transition was expected to the 9/2+[624] bandhead in 181Hf, which was previously assigned at 68 keV. However, the only L = 0 transition observed was to a level at an excitation energy of 600 ± 5 keV, requiring that this new level be assigned as the 9/2+[624] state. An attempt to observe gamma transitions deexciting this level in a (t, pγ) coincidence experiment yielded negative results. This implies that the 600 ± 5 keV level either has a half-life of [Formula: see text] or decays to an isomeric level by means of a low energy [Formula: see text] unobserved transition. The irregular spacing of possible 9/2+[624] band members suggests that the 11/2+[615] orbital is located near the 9/2+[624] state and perturbs the level spacing by Coriolis mixing.