The level structure of 184Os from 184Ir decay and 185Re(p, 2nγ) in-beam spectroscopy

doi:10.1016/0375-9474(73)90771-9

Nuclear Physics A

Volume 211, Issue 1, 27 August 1973, Pages 165-188

https://doi.org/10.1016/0375-9474(73)90771-9 Get rights and content

Abstract

Levels of ¹⁸⁴Os populated in the decay of 3.1 h ¹⁸⁴Ir and in the ¹⁸⁵Re(p, 2nγ) reaction have been investigated. The measurements included γ-ray singles, β⁺ ray endpoint, conversion coefficient, β⁺-γ coincidence and detailed γ-γ coincidence determinations. The results have established an extensive ¹⁸⁴Os level scheme, which includes well developed ground state, γ-vibrational and K = 3 octupole bands and which accommodates all the intense transitions observed in both the radioactivity and in-beam γ-ray measurements. Deviations of the level energies in the K^π = 0⁺and K^π = 2⁺ bands and of the interband reduced transition probabilities from the predictions of the strong-coupling model are discussed in terms of the rotationvibration interaction, and the systematics of the octupole vibrational excitations in even-mass W and Os nuclei are reviewed. It is concluded that the ¹⁸⁴Ir ground state configuration has a spin of 5, and that it contains large admixtures of K = 0 or K = 1 character.

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Nuclear Data Sheets for A = 184
2010, Nuclear Data Sheets
Nuclear structure and decay data for all nuclei with mass number A=184 (Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi) have been evaluated, and the corresponding level schemes from radioactive decay and reaction studies are presented. This evaluation supersedes the previous publication (R.B. Firestone, Nuclear Data Sheets 58, 243 (1989) (literature cutoff date 1 June 1989)) and subsequent revisions of high spin data for several nuclides by Huo Junde (31 July, 1995) and evaluations by C.M. Baglin for ¹⁸⁴Au, ¹⁸⁴Pb and the new nuclide ¹⁸⁴Bi (literature cutoff dates 4 April 2003, 28 July 2003 and 21 January 2004, respectively). The present evaluation includes literature available by 1 October 2009. Subsequent to those evaluations, (HI, xnγ) studies have contributed significantly to our knowledge of the structure of ¹⁸⁴Re (2005Wh04), ¹⁸⁴Os (2002Sh21, 2002Wh01, 1998Sh36), ¹⁸⁴Hg (1995De30, 1995Sf01) and ¹⁸⁴Au (2004Zh38). Additional information on the level structure of ¹⁸⁴W has become available from new thermal neutron capture measurements (2003Bo52, 2004Lo22, 2007ChZX), from detailed $(p, t)$ reaction studies (2006Me25), new Coulomb excitation (1991Wu05) and $(γ, γ^{'})$ (1993He15) studies, and from the ¹⁹⁸Pt(¹³⁶Xe,Xγ) reaction (2004Wh02); knowledge of ¹⁸⁴Pt has benefited from a new ¹⁸⁴Au ε decay study (2006KrZT, 1992Xu02, 1992Xu06, 1992XuZY), but this decay cannot yet be normalized due to the mixed parentage of the sources used.
Competing phenomena: High-seniority excitations and γ-softness in 184Os
2002, Nuclear Physics A
The nuclear structure of the stable nucleus ¹⁸⁴₇₆Os has been studied including five newly identified rotational bands built on 2-quasiparticle K^π=0⁺, 6⁻, 8⁻ couplings. The excitation energies of the proposed multi-quasiparticle excitations are in good agreement with predictions of blocked BCS calculations. The interaction responsible for the first band crossing, caused by a high-K tilted 2-neutron configuration, is calculated and a new interpretation presented for the yrast states after the interaction. A second crossing with an aligned s–β band is also reported. The yrast behaviour at high spins is dominated by a wealth of short-lived (nanoseconds and shorter) high-K levels. The low reduced hindrances for intrinsic state decays are discussed, and attributed to the triaxial shapes and fluctuations predicted by configuration-constrained potential-energy-surface calculations. Comparisons with neighbouring nuclei are made.
Low-spin non-yrast states and collective excitations in 174Os, 176Os, 178Os, 180Os, 182Os and 184Os
1994, Nuclear Physics, Section A
Excited states in the range of isotopes ^{174, 176, 178, 180, 182, 184}Os, populated in the β-decay of ^{174, 176, 178, 180, 182, 184}Ir parent activities have been identified using γ-ray singles and coincidence techniques, utilising the high efficiency of a Compton-suppressed array, and conversion electron techniques. Many new states at low excitation energies have been identified, complementing the level schemes previously established from in-beam studies. The new states include excited 0⁺ states in ¹⁷⁴Os, ¹⁷⁶Os ¹⁷⁸Os and ¹⁸⁰Os. A large body of data on decay properties, spins and parities, and relative E2 and E0 matrix elements has been obtained. The systematics of the quasi-β and quasi-γ bands is discussed. Some detailed analyses in terms of the schematic band-mixing model are presented, incorporating reproduction of the yrare states in the fits. In particular, the proposed interpretation of the anomalous low-frequency alignment gains in the yrast positive-parity states, as a consequence of mixing with a low-lying intruder band, is confronted. The B(E0)/B(E2) ratios are over-estimated by this model although their form (spin and isotope dependence) is reproduced. Better agreement is obtained within the IBM, which uses however reduced effective charges to match experiment. Absolute measurements of the B(E0) and B(E2) values may be necessary to distinguish between the models and test conjectures of shape differences.
Nuclear data sheets for A = 184
1989, Nuclear Data Sheets
Decay of doubly-odd nucleus 184Ir
1989, Nuclear Physics, Section A
The ¹⁸⁴Ir β⁺/EC decay has been investigated using the ISOCELE facility. A detailed ¹⁸⁴Os level scheme has been obtained. Spin and parity assignments have been deduced from transition multipolarities. The Q_β+ value has been measured to be 3260±70keV by means of a solid-state ΔE−E telescope and log ft values have been calculated for the levels which are the most clearly fed. Two highly converted transitions have been pointed out. Contrary to results previously reported, the ground-state band of ¹⁸⁴Os is not directly populated. It is concluded that the ¹⁸⁴Ir ground state has spin and parity value I^π = 4⁻ or 5⁻ with projection value K which may be 4 and/or 5. The ¹⁸⁴Os levels are compared to those of the other osmium isotopes and the structure of the 3₁⁻ level is discussed.
Decay of high-spin isomers in Os nuclei by barrier penetration
1988, Nuclear Physics, Section A
A decay scheme for the 130±20 ns high-spin isomer in ¹⁸²Os has been established. The excitation energy of the isomer is 7049±1 keV and it has I^π = 25⁽⁺⁾. A 2.4% decay directly to the yrast 24⁺ level at 5988 keV is observed. In ¹⁸⁴Os a 20±5 ns isomer is observed at 2366±1 keV excitation energy with I^π = 10⁺. Again, direct transitions into the yrast 8⁺ and 10⁺ levels are observed. Contrary to previous speculations, there is no compelling evidence for stable triaxial shapes in the structure of the levels through which the isomers decay. The abnormally short half-lives observed, as well as the unusual decay patterns, are best understood in terms of a γ-soft nuclear potential. Motion in the γ-direction allows the isomer to decay via barrier penetration from an axially symmetric prolate shape with the angular momentum along the nuclear symmetry axis (deformation aligned state) via oblate shapes to another prolate shape with the angular momentum perpendicular to the nuclear symmetry axis (rotation-aligned state).

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^†: Work supported by the US Atomic Energy Commission.

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Nuclear Physics A

Abstract

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Nuclear Data Sheets for A = 184

Competing phenomena: High-seniority excitations and γ-softness in <sup>184</sup>Os

Low-spin non-yrast states and collective excitations in <sup>174</sup>Os, <sup>176</sup>Os, <sup>178</sup>Os, <sup>180</sup>Os, <sup>182</sup>Os and <sup>184</sup>Os

Nuclear data sheets for A = 184

Decay of doubly-odd nucleus <sup>184</sup>Ir

Decay of high-spin isomers in Os nuclei by barrier penetration