γ-ray spectroscopy ofBi191,193

Abstract

Prompt and delayed ␥ rays from 191,193 Bi have been identified using the recoil-decay tagging, isomer tagging, and recoil gating techniques, resulting in extensive level schemes for both nuclei. Excitation energies of the isomeric 13/ 2 + states have been established and oblate strongly coupled bands built on them have been observed. The nearly spherical 9 / 2 − ground-state bands appear to be crossed by more oblate-deformed lowlying structures. The properties of the bands feeding the 1 / 2 + intruder states indicate some structural change between 193 Bi and 191 Bi. The deformation associated with each of these states has been extracted from total Routhian surface calculations which also reveal the development of prolate minima with decreasing neutron number. B͑M1͒ / B͑E2͒ ratios have been measured for the observed strongly coupled bands in order to resolve the intrinsic excitations. The observed quasiparticle structures in 193 Bi and high-spin isomers both in 193 Bi and 191 Bi are interpreted based on the coupling of the odd proton to the even-even Pb core.

Detailed spectroscopy of Bi195

“…Band 1 undergoes a sharp bandcrossing above I π = 25/2 + . Experimental intensity ratios R exp and linear polarization asymmetry factors, listed in Table I, support the previously assigned M1 and E2 character for the transitions reported by Nieminen et al [7] and extend this information up to the topmost members of the band. A γ -ray spectrum gated on the 154 keV transition, placed just above the band crossing, is shown in Fig.…”

“…In 195 Bi the corresponding state is also known, but the feeding level structure has remained unobserved. An isomeric state with T 1/2 = 3 μs has been reported in 193 Bi [7]. Although the depopulating transition was not observed, this was tentatively assigned with a spin and parity of 29/2 − based on systematics in heavier odd-mass Bi nuclei [4].…”

“…The level scheme presented in the earlier study by Nieminen et al [7] has been extended. Many and the related γ -ray transitions are listed in Table I.…”

“…The 13/2 + bandhead of Band 1 has a half-life of 153(10) ns [7]. The band structure feeding the isomeric 13/2 + state (Band 1) was previously observed up to I π = (29/2 + ), where the statistics did not allow firm assignment of the two uppermost states.…”

“…In previous studies [7,8], strongly coupled rotational bands based on the proton 13/2[606] and 7/2[514] Nilsson orbitals have been observed in 191,193 Bi nuclei, in contrast to 195 Bi, where very limited spectroscopic information exists [9,10]. Irregular bandlike structures built on the 1/2 + proton intruder state have been observed in 191 Bi and 193 Bi.…”