Rotation-aligned bands inHg196

Abstract

Levels inHg have been studied by the Pt(n, 4n) reaction and the high-spin level scheme of ' Hg has been considerably extended. Backbending in both positive and negative parity yrast level sequences is discussed within the cranked shell model description. ' NUCLEAR REACTIONS '96Pt(n, 4n), E =48.6 MeV; measured E, I (9), ' t~y2(y), y-y coin; ' Hg deduced high-spin levels, J, 7r.The high-spin level spectra of the transitional Hg nuclei, both even and odd 3, have been intensively studied. ' ' The even-parity yrast levels of ' ' '' ' ' Hg exhibit, in the vicinity of I = 10, acute backbending behavior that has been attributed to the intersection of the ground bands by either 7rh~~y2 or vi~3'' rotation-aligned S bands. A longstanding dispute about the nature of these S bands was recently settled by g-factor determinations, which showed them to have vi~3 @ rotation-aligned structure, and by the first observations 9 of key 12+~10+ low-energy transitions in Hg. Other interesting spectral features seen systematically across the even-A Hg nuclei are semidecoupled 5 bands' with dominant microscopic components of the type (vit3~q, vj). The properties of the lower-spin members of these bands are reproduced well in model calculations. " %e report here the results of a study of levels in ' Hg by the reaction '96Pt(n, 4ny). These results are much more extensive than those recently reported,~and they clarify some important aspects of the ' Hg level structure.The experiments were performed by bombarding a selfsupporting 650 pg/cm Pt foil, enriched to 97oio in '96Pt, with 48.6-MeV n-particle beams from the Michigan State University Cyclotron. The measurements included y-ray singles with a 10% Ge(Li) and a low-energy photon spectrometer, y-ray angular distributions by intensity measurements at five angles spanning the range 90' -157', half-life determinations between the cyclotron beam-bursts, and comprehensive year coincidences with two large Ge(Li) detectors. Representative yy coincidence spectra illustrating the quality of the data are shown in Fig. 1. Those y rays observed to be in coincidence with the known 426-keV 2+ 0+ and 636-keV 4+ 2+ transitions were assigned to Hg; their energies, intensities, and angular distribution coefficients are listed in Table I. The ' Hg level scheme shown in Fig. 2 is based firmly on the yy coincidence results. The positive parity levels up to 14+ and the odd-spin negative parity levels up to 11 have been established previously, ' and half-lives of 5.1, 5.1, and 3.5 ns, respectively, have been reported' 9 for the 7 10+, and 12+ levels. Our lifetime results are consistent with these values, but we could not resolve the 10+ and 12+ half-lives as cleanly as the Bonn group did in their decisive conversion electron timing measurements.However, we find no evidence for the proposeds" 278-keV 10+ 9 2000-223 kev 1000-2000-478 keV looo-LJJ

Rotational structures in Hg196

“…Coincidence relationships from the present experiment confirm the levels and transitions of the previously reported [18,27] even-spin negative-parity sequence (Band 3) up to 3237 keV, and allow an extension of the band up to a 24 − level at 6778 keV by placing the sequence of γ rays with energies of 665, 303, 343, 509, 723, and 999 keV as indicated in Fig. 1.…”

Shape coexistence in neutron-deficient Hg isotopes studied via lifetime measurements inHg184,186and two-state mixing calculations

“…Good agreement is found for the majority of yrast transitions, even for cases where the states are strongly mixed. The observed discrepancies for I ≥ 6 in 186 Hg may indicate a breakdown of the simple two-band picture as other structures begin to influence the yrast states [43,44]. For the nuclei presented in Fig.…”

Descriptive New features of high angular momentum rotational states in some rear-earth nuclei

“…In the earlier work (see Ref. [9][10][11][12][13][14] it was established that the bands which cross the ground and 13/2 bands are the two-and three-quasineutron (i 13/2 ) aligned bands in the even and odd isotopes, respectively. The 5 -and 8 -bands semi-decoupled (see Ref.15) and are intersected by the bands in which two additional i 13/2 neutrons are aligned.…”