Measured Magnetic Moments and Shape Coexistence in the Neutron-Deficient NucleiP184,186,188

Abstract

A novel implantation-decay technique has been employed to measure the magnetic moments of the 2 1 1 states in the neutron-deficient nuclei 184 Pt, 186 Pt, and 188 Pt. The magnetic moment systematics for the even Pt isotopes now extend from 184 78 Pt 106 to 198 78 Pt 120 , spanning the upper half of the valence neutron shell. Despite the prolate-to-oblate shape transition near A 190, they remain remarkably constant. The g͑2 1 1 ͒ values for 184,186,188 Pt are consistent with shape-coexistence models in which the deformed configuration has a larger effective number of valence protons than the less-deformed configuration.

Platinum nuclei: Concealed configuration mixing and shape coexistence

“…Early calculations by Kumar and Baranger that were quite consistent with the data [61] indicated a change from a prolate towards a more oblate ground-state shape between A = 188 and A = 190 and were later substantiated by studies from Bengtsson et al [62]. Stuchbery et al [20] analysed gyromagnetic factors starting from the two-band mixing study carried out by Dracoulis et al [63], in which the mixing between a regular and an intruder configuration consistent with the measured B(E2) and with E0 measurements by Xu et al [64] was extracted. The calculations by Stuchbery et al [20] pointed out that the data cannot be described using only a single configuration but are consistent with the mixing of two configurations.…”

“…A, for our purpose, particularly interesting set of data are the g-factor measurements for the 2 + 1 state in the mid-shell 184,186,188 Pt nuclei [20]. The data display a rather flat behaviour as a function of the neutron number in the vicinity of mid-shell.…”

“…Stuchbery et al [20] analysed gyromagnetic factors starting from the two-band mixing study carried out by Dracoulis et al [63], in which the mixing between a regular and an intruder configuration consistent with the measured B(E2) and with E0 measurements by Xu et al [64] was extracted. The calculations by Stuchbery et al [20] pointed out that the data cannot be described using only a single configuration but are consistent with the mixing of two configurations. In particular, the need of an increased number of active proton pairs for the description of the A = 184, 186, 188 results was demonstrated.…”

High-spin structure in 187Pt

“…Band 4 is built on the ground state, which was suggested to be the ν3/2 − [512] Nilsson configuration [3][4][5] . The hyperfine structure measurements strongly suggested a triaxial shape for the ground state of 187 Pt [3][4][5] , which was supported by the TRS calculations.…”

“…Different structures associated with prolate, oblate, and triaxial shapes within the same nucleus have been identified experimentally [1,2] , and the ground-state shape transitions for the isotopic chains have been observed [3][4][5] . The isotope shift measurements have shown a sharp change of the nuclear charge radius between 188 Pt and 186 Pt [3][4][5] , suggesting a ground-state shape transition from the near oblate shape for the Pt nuclei with A≥188 to the prolate shape for A≤186. Therefore, the spectroscopic information of 187 Pt is of particular interest as it lies between the two nuclei 186 Pt and 188 Pt where the change in the collective structure should be the most drastic.…”