Diverse collective excitations in159Erup to high spin

Abstract

A spectroscopic investigation of the γ decays from excited states in 159 Er has been performed in order to study the changing structural properties exhibited as ultrahigh spins (I > 60h) are approached. The nucleus 159 Er was populated by the reaction 116 Cd( 48 Ca,5nγ) at a beam energy of 215 MeV and the resulting γ decays were studied using the Gammasphere spectrometer. New rotational bands and extensions to existing sequences were observed, which are discussed in terms of the cranked shell model, revealing a diverse range of quasiparticle configurations. At spins around 50h there is evidence for a change from dominant prolate collective motion at the yrast line to oblate non-collective structures via the mechanism of band termination. A possible strongly deformed triaxial band occurs at these high spins, which indicates collectivity beyond 50h. The high spin data are interpreted within the framework of cranked Nilsson-Strutinsky calculations.

Core excitations beyond maximally aligned configurations in123I

“…The first case was the I π = 40 + state in 158 Er [12], where a neutron of h 9/2 f 7/2 character is antialigned relative to the maximally aligned configuration with I π = 46 + . Similar states were found later also in 156 Er, 157 Er, and 159 Er [13][14][15]. In the mass-125 region, in addition to 125 I, such a state was reported only in 121 I [10].…”

High-spin spectroscopy of140Nd

“…This energy is calculated in a mesh of deformations ε 2 , γ , and ε 4 , and the minimum is searched as a function of these parameters. In the calculations of the single-particle energies, we have used the so-called A = 150 parameters [25], which are known to give a good description of the low-deformation configurations of nuclei with a few particles outside the 146 Gd core; see, e.g., [26] and references therein. By introducing some minor approximations which are essentially negligible at the small deformations of the triaxial 140 Nd bands, it becomes possible to label the orbitals as belonging to a specific N shell and as being of high-j (intruder) or low-j character.…”

General properties of terminating bands in the A = 110 and A = 160 mass regions

“…The mentioned assignments for the Ho isotopes, 155−157 Ho, are in agreement with the result of the neighboring nucleus having one more proton, Er isotopes. The favored terminating configurations in 156−159 Er are included four protons in the h 11/2 orbital with no proton hole [9,[35][36][37]. Therefore, for holmium isotopes, as expected, the bands terminate within [03] proton configuration with more probability than the [14] proton configuration.…”