γ-ray spectroscopy approaching the limits of existence of atomic nuclei: A study of the excited states ofPt168andPt

Abstract

Excited states in the N = 90 and N = 91 Pt nuclei have been investigated using the jurogam and great spectrometers in conjunction with the ritu gas-filled separator. These nuclei were populated via the reactions 92 Mo(78 Kr, 2n) and 94 Mo(78 Kr, 3n) at 335 and 348 MeV, respectively. The recoildecay tagging technique has been used to correlate prompt γ radiation with the characteristic α decays of 168 Pt and 169 Pt. A γ-γ analysis has allowed a level scheme for 168 Pt to be reported for the first time and the level scheme for 169 Pt to be extended. The excitation energies of the proposed positive-parity yrast states of 168 Pt are compared with calculations based on the interacting boson model and found to be in excellent agreement. These data show a continuation of the trend towards vibrational nuclei as the N = 82 shell gap is approached. In addition, new excited states constituting two decay paths have been discovered in 169 Pt.

First observation of excited states of173Hg

“…In the inset to Fig. 1 is shown the time distribution of α particles, consistent with the known decay properties of 173 Hg, detected within 500 ms of an implanted recoil and which were followed by α decays of 169 Pt (E = 6695(5) keV, T 1/2 = 6.99(10) ms [26]) in the same pixel. The form of this plot follows the method outlined by Schmidt et al [27] in which the difference in time between implantation and decay (dt) are plotted on a logarithmic scale.…”

Quasiparticle alignments andα-decay fine structure of175Pt

“…For the higher-lying coexisting configuration a prolate deformation is predicted, whereas in the heavier platinum isotopes, A = 180-186, this configuration is observed to become the ground state [2,[5][6][7]. The well deformed and the weakly deformed configurations are predicted to be almost degenerate in 178 Pt [8], and in the lighter platinum A 176 isotopes the weakly deformed configuration forms the ground state [3,[9][10][11]. Thus, 175 Pt is situated in a transitional region, where the weakly deformed triaxial configuration forms the ground state, but a well deformed configuration is sufficiently low lying to cause perturbations in the measured yrast band.…”