High-Spin Level Systematics inPt186−194and Rotation-Alignment Coupling

Rotation-aligned isomer and oblate collectivity inPt196

“…Gamma softness in varying degrees is a feature common to all Pt isotopes owing to the relatively small number of valence nucleons. For the doubly-even Pt isotopes, a rather sudden change in the energy sequence of the yrast, positive-parity, structure is evident around 10-12 in 188−194 Pt [2,5]. In fact, the 12 + state is isomeric, and the rotational sequence built on this level is characterized by a moment of inertia much larger than that of the ground-state band.…”

“…While collectivity diminishes with increasing neutron number, oblate rotation-aligned states tend to be favored at high spin over prolate excitations, in isotopes of Hf (Z=72) to Hg (Z=80) [1][2][3][4]. Substantial high-spin information is available for lighter Pt isotopes [2,5] which are accessible through heavy-ion fusion evaporation reactions. Isotopes of Pt (Z=78), beginning with 196 Pt, can be reached only through either inelastic excitation, multi-nucleon transfer or projectile fragmentation reactions [6,7].…”

Evidence for shape coexistence in186Pt

“…Previous knowledge about high-spin states in 186pt results from studies of Piiparinen et al [1] who established the gb up to U= 14 + and from half life studies of Richter et al [5] who searched for subnanosecond isomers by recoil-shadow conversion-electron spectroscopy. In order to investigate the shape evolution of 186pt at higher rotational frequencies it was necessary (i) to extend the yrast band to higher spins and (ii) to search for side bands.…”

“…Arguments for a gradual change from predominantly prolate shape (+ 30~ 7 > -30~ for Pt nuclei with mass number A < 184 to predominantly oblate shape (-30~ 7> -90 ~ for those with mass number A>188 are (i) that the i13/z quasineutron bands are decoupled in 187, 189, 191,193pt [1] but strongly coupled in 18spt [2,3] and (ii) that the excitation energies of the ground band (gb) levels in the even-mass Pt nuclei change from small values for light Pt isotopes to large values for the heavy ones [4,5]. Evidence for shape coexistence in the Pt nuclei has not been given hitherto but is suggested (/) because a prolate-oblate shape coexistence was found in neighbouring oddmass Au nuclei by the observation of decoupled n h 9/2 and decoupled nh 11/2 bands [6][7][8] and (ii) since lowlying excited 0 + levels were observed in the even-mass nuclei 182-194pt.…”

Isomers and oblate collectivity at high spin in neutron-rich Pt isotopes

“…Proton-rich Pt isotopes have been studied rather extensively e.g. [4,8,9], a e-mail: sujit.tandel@cbs.ac.in and found to exhibit well-developed rotational bands both near the ground states and at high spin. With increase in neutron number from the lightest stable isotope 190 Pt (N=112) to the heaviest 198 Pt (N = 120), the decrease in ground state deformation and collectivity is evidenced by the increase in 2 + 1 excitation energy in even-A nuclei accompanied by a corresponding reduction in B(E2; 2 + →0 + ) values.…”