High-spin states in 183Hg and shape coexistence in the odd-mass mercury isotopes

doi:10.1016/0375-9474(95)00080-K

Nuclear Physics A

Volume 589, Issue 1, 26 June 1995, Pages 129-159

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Abstract

High-spin states in ¹⁸³Hg have been identified using the reaction ¹⁵⁵Gd(³²S,4n). Three prolate-deformed rotational bands associated with the $12^{−} [521]$ , $72^{−} [514]$ and mixed $i_{132}$ neutron orbitals are observed, while the existence of an oblate $132^{+}$ bandhead is inferred, implying co-existing prolate and oblate nuclear shapes. A two-band mixing model used to fit the state energies of the $i_{132}$ neutron bands in ^183,185,187Hg gives parameter values which are consistent with the existence of two bands with different deformations. The B(E2) ratios of the intra- and inter-band transitions in these coexisting bands are also investigated. Many of the features can be reproduced but difficulties remain, for example the results are not consistent with the assumption of coexistence between simple prolate and oblate shapes, a problem noted previously for the even-mass isotopes. Systematics of the prolate-oblate energy differences show that the energy of the prolate well relative to the oblate well is ∼ 350 keV lower in the odd-mass isotopes than in the even-mass isotopes. Possible reasons for this are described. The nature of the first alignment in the prolate bands in the mercury isotopes is discussed within the cranked shell model.

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First observation of the decay of the 13/2+ isomer in 183Hg and B(M2) systematics of neutron transitions across the nuclear chart
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Citation Excerpt :
To reduce possible degradation of the target due to beam heating, four target sectors were mounted on a rotating wheel, and a magnetic steerer was used to wobble the beam ±2.5 mm horizontally across the target [15]. In 183Hg, several prolate-deformed rotational bands have been established experimentally [19–21], e.g., the 1/2−[521] g.s. band and a “floating” 7/2−[514] band, which are also known in the neighboring deformed nuclides, e.g., 181,185Hg and 181,183Pt [27]. Selected low-lying levels from these bands, of possible relevance to the decay of the 13/2+ isomer, are shown in Fig. 2.
The decay of the 13/2⁺ isomeric state in ¹⁸³Hg was observed for the first time following the α decay of the 13/2⁺ isomer in ¹⁸⁷Pb produced in the ¹⁴²Nd(⁵⁰Cr, 2p3n) reaction. Using $α - γ$ delayed coincidence measurements, the half-life of this isomer was measured to be 290(30) μs. This isomer is proposed to deexcite by an unobserved low-energy M2 transition to the known 9/2⁻ member of a strongly prolate-deformed 7/2⁻[514] band, followed by a 105-keV M1 transition to the bandhead. A lower limit of B(M2) ≥ 0.018 W.u. was deduced for the unobserved transition. The presumed retardation is proposed to be due to the notable shape change between the initial, nearly spherical, and the final, strongly deformed, states. A similar scenario is also considered for the 13/2⁺ isomer in ¹⁸¹Hg, suggesting both are cases of shape isomers. The $B (M 2)$ systematics of neutron transitions across the nuclear chart is discussed.
Lifetime measurements of excited states in 169,171,173Os: Persistence of anomalous B(E2) ratios in transitional rare earth nuclei in the presence of a decoupled i<inf>13/2</inf> valence neutron
2021, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Lifetimes of low-lying excited states in the $ν i_{13 / 2^{+}}$ bands of the neutron-deficient osmium isotopes ^169,171,173Os have been measured for the first time using the recoil-distance Doppler shift and recoil-isomer tagging techniques. An unusually low value is observed for the ratio $B (E 2; 21 / 2^{+} \to 17 / 2^{+}) / B (E 2; 17 / 2^{+} \to 13 / 2^{+})$ in ¹⁶⁹Os, similar to the “anomalously” low values of the ratio $B (E 2; 4_{1}^{+} \to 2_{1}^{+}) / B (E 2; 2_{1}^{+} \to 0_{gs}^{+})$ previously observed in several transitional rare-earth nuclides with even numbers of neutrons and protons, including the neighbouring ^168,170Os. Furthermore, the evolution of $B (E 2; 21 / 2^{+} \to 17 / 2^{+}) / B (E 2; 17 / 2^{+} \to 13 / 2^{+})$ with increasing neutron number in the odd-mass isotopic chain ^169,171,173Os is observed to follow the same trend as observed previously in the even-even Os isotopes. These findings indicate that the possible quantum phase transition from a seniority conserving structure to a collective regime as a function of neutron number suggested for the even-even systems is maintained in these odd-mass osmium nuclei, with the odd valence neutron merely acting as a “spectator”. As for the even-even nuclei, the phenomenon is highly unexpected for nuclei that are not situated near closed shells.
Nuclear Data Sheets for A = 183
2016, Nuclear Data Sheets
Evaluated nuclear structure and decay data for all nuclides with mass number A=183 (Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb) are presented here. At, Po and Fr have not yet been observed, but for prediction of ground state and/or isomer properties see, e.g., 2015Bh08 (At, Fr), 2013Ba41 (Tl), 2013Ho05 (Po). This evaluation includes structure and decay data information available by 15 April 2015 and supersedes that by R.B. Firestone published in Nuclear Data Sheets 65, 589 (1992) (literature cutoff 9 January 1991), and subsequent revisions by C.M. Baglin for ¹⁸³Au in ENSDF database (literature cutoff 13 March 1999), ¹⁸³Hg in Nuclear Data Sheets 91, 117 (2000) (literature cutoff 25 September 2000), ¹⁸³Tl in Nuclear Data Sheets 95, 49 (2002) (literature cutoff 1 January 2002) and ¹⁸³Pb in ENSDF (literature cutoff 6 January 2003).
Since the prior Nuclear Data Sheets publication of this mass chain: ¹⁸³Yb (2012Ku26) and ¹⁸³Pb (2006An11, 2006Se18, 2007De09, 2009Se13) have been observed; our knowledge of high–spin states has been significantly expanded for ¹⁸³Ta (2009Sh17), ¹⁸³W (1999Sa60), ¹⁸³Re (1998Ha51, 2001Sh41), ¹⁸³Au (2002Jo18, 2005So01) and ¹⁸³Tl (2001Mu26, 2004Ra28); a large amount of new structure information for ¹⁸³W has been obtained from transfer reactions (1997Pr02, 2011Bo09), (n,n'γ) (1993Pr09) and thermal neutron capture (1993Pr09, 1997Pr02, 2011Bo09, 2014Hu02), as well as from the two–photon cascade study by 2005Su29.
First observation of excited structures in neutron-deficient 179Hg: Evidence for multiple shape coexistence
2002, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Excited structures in the neutron-deficient nucleus ¹⁷⁹Hg have been established for the first time using the Gammasphere spectrometer in conjunction with the fragment mass analyzer. Competing states originating from three different minima associated with nearly spherical, oblate, and prolate deformations were found. This result can be contrasted with the situation in heavier odd-mass Hg isotopes where only two minima (oblate and prolate) have been seen. The implications of these three shapes at low spin and excitation energy are discussed in the general context of shape coexistence in this mass region.
First observation of excited structures in neutron deficient, odd-mass Pt, Au and Hg nuclei
2001, Nuclear Physics A
Nuclear data sheets for 183Hg
2000, Nuclear Data Sheets
Nuclear structure data pertaining to ¹⁸³Hg have been compiled and evaluated, and incorporated into the ENSDF data file. This evaluation of ¹⁸³Hg supersedes the previous publication (R.B. Firestone, Nuclear Data Sheets 65, 589 (1992) (literature cutoff date 9 January 1991)), and includes literature available by 25 September 2000. The newly incorporated references are: 1992BoZO, 1993Bi17, 1995Au04, 1995La10, 1995Sh04, 1999An10, 1999An36, 1999Ba45, 2000By02.

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¹: Joint appointment with Department of Physics and Theoretical Physics, The Faculties, The Australian National University, Canberra ACT 0200, Australia.

²: Present address: Institute of Physics, Odense University, 55 Campusvej, Odense, DK-5230M, Denmark.

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Nuclear Physics A

Abstract

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Cited by (29)

First observation of the decay of the 13/2<sup>+</sup> isomer in <sup>183</sup>Hg and B(M2) systematics of neutron transitions across the nuclear chart

Lifetime measurements of excited states in <sup>169,171,173</sup>Os: Persistence of anomalous B(E2) ratios in transitional rare earth nuclei in the presence of a decoupled i<inf>13/2</inf> valence neutron

Nuclear Data Sheets for A = 183

First observation of excited structures in neutron-deficient <sup>179</sup>Hg: Evidence for multiple shape coexistence

First observation of excited structures in neutron deficient, odd-mass Pt, Au and Hg nuclei

Nuclear data sheets for <sup>183</sup>Hg