Coupling of single proton con_gurations to collective core excitations in 162Yb: the nucleus 161Tm.

Abstract

There has been controversy over the past years as to whether deformed nu- clei are subject to quadrupole vibrations (gamma and _), particularly the _ vibrations. Pertaining the gamma K = 2+ vibrations, experimental evidence has been more or less consistent, confirming they indeed exist. On the other hand the situation remains complex for the _ vibrations which are charac- terized by the first low lying 0+2 excited state. Using a concept involving pairing it has been suggested that the K = 0+2 states are simply lowered into the pairing gap by configuration dependent pairing involving the [505]11=2ð€€€ neutron orbital. In attempt to understand the true nature of the collective vibrations in relation to the \pairing theory" a suitable approach is studying nuclei in the N = 88 ð€€€ 90 region containing the [505]11=2ð€€€ orbital. The current work seeks to get more insight on the microscopic nature of the aforementioned by studying the spectroscopy of 161Tm. The nucleus of interest 161Tm, was populated using the 152Sm(14N,5n)161Tm reaction with the aid of the AFRODITE array. The nucleus 161Tm is axially symmetric and it is a relatively good assumption that its core retains the same symmetry. As such the core will behave in a manner similar to that of a neighbouring even-even deformed nucleus. Therefore in this study we were searching for high K structures where the odd proton in 161Tm couples to collective excitations in 162Yb (the core) which has a very low lying K=2+ gamma band. The known level scheme of 161Tm has been extended at low spin with new transitions observed. Linear polarization measurements and Direct Correlations for Oriented states (DCO) ratios were performed to confirm the spin and parity assignments of old and new transitions. The semi-classical model together with alignments has been used to meaningfully describe the quantum behaviour of the collective structures observed in this work. Systematic comparisons have also been used to further understand the structural behaviour of band structures observed in this study. Furthermore experimental B(M1)/B(E2) values for bands involving the [505]11=2ð€€€ orbital and other observed strong coupled bands were obtained to confirm quasi-particle configurations.