F. M. Bernthal

Rotational bands in 170Yb observed following (α,xn) reactions

Abstract At least seven side bands, with Kπ = (0+), (1−), (2+), (3−), 4−, 6−, and 7−, have been identified in 170Yb up to high spin, using γ-ray techniques following (α, 2n) and (α, 4n) reactions. Backbending in the positive-parity yrast band is confirmed, and candidates for low-spin members of the S-band are found. The negative-parity yrast band has behaviour characteristic of both strong coupling and decoupling. These properties, together with those in the other negative-parity side bands, are interpreted as arising from Coriolis effects on the quasiparticle configurations, and the experimental results are compared with a two-quasipartiele-plus-rotor calculation. Evidence of ΔK = 2 mixing is found in the K = (3) side band. The relationship between the moments of inertia of the positiveparity and negative-parity yrast bands in the N = 100 isotones is discussed in the framework of a simple empirical model, giving insight into the presence or absence of backbending. The negativeparity yrast bands in the N = 100 isotones are compared. Their significant differences are qualitatively reprodued in two-quasiparticle-plus-rotor calculations.

High-spin level systematics in 177–182W: Yrast band anomaly in 180W☆

Abstract High-spin levels in 177–182W have been populated in (α,χnγ) reactions. Backbending-type behavior appears most prominently in 180W. The role of i 13 2 neutrons and h 9 2 protons in the 180W yrast behavior is examined. A strongly-coupled Kπ = 10+ band structure is identified in 182W, the first seniority-two i 13 2 configuration to be characterized in a deformed nucleus.

High-spin neutron hole excitations in light odd-A Pb nuclei☆

Abstract The high-spin level structures of 195,197,199,201,203 Pb have been investigated by ( α , x n γ ) and ( 3 He , x n γ) spectroscopy. The resulting level schemes are interpreted in terms of the weak coupling of an ν i 13 2 hole to known states of the even- A core nuclei.

Evidence for triaxial shapes in Pt nuclei

Abstract Positive parity levels in 191Pt obtained from (α, xnγ) reactions and β-decay are presented as a first example of a rather complete i 13 2 level family. The spectrum confirms triaxial shapes found before from h 11 2 and h 9 2 proton structures in this mass region. In addition to the usual decoupled yrast band, a second ΔI = 2 band within the i 13 2 family, built on a low-lying j−1 = 11 2 state, is observed in agreement with theory.

High-spin rotational levels in 178W populated in the 177Hf(α, 3nγ) reaction☆

High-spin rotational levels in 178W were populated in the 177Hf(α, 3nγ) reaction. The yrast sequence of states is identified to spin 16 and is contrasted with similar data for 180W and 182W. Two probable two quasi-neutron bands with Kπ = 6+ and 7− are characterized from derived gK values and decay patterns. The Kπ = 2− octupole band is identified to spin 13, and the higher-spin members of the lowest Kπ = 0+ band are placed. A 35 ns isomer is identified at 3528 keV.

Rotational and intrinsic structure of 182W from the (α, 2nγ) reaction and decay of 182mRe☆

Abstract The 180Hf(α, 2nγ) reaction was used to populate states in 182W. In-beam γ-ray spectroscopy experiments result in assignment of 59 levels to the 182W level scheme. Eleven rotational bands are identified, and most of these are characterized. A previously reported 1.4 μs isomer is characterized as the Kπ = 10+ triplet coupling of 9 2 + [624] and 11 2 + [615] neutrons, the first seniority two i 13 2 configuration to be identified in the rare-earth deformed region. The strongly coupled band built on this isomer apparently becomes yrast above spin 16. Data from EC β+ decay of 64 h 182mRe were used to supplement the in-beam data.

Evidence for hexadecapole vibrations in A ≈ 170 deformed nuclei; New results for 168Yb☆

Abstract Dominating proton structure has been identified in the Kπ=3+ band of 168Yb, contrasting with neutron structure in the corresponding band of 172Yb. A region of low-lying Kπ=3+ bands is now established, with N=98−104, Z=68−72. For all stable nuclei in this region, the IπK=4+3 state is excited by inelastic deutron scattering.

Negative-parity yrast band in 170Yb: Rotation-aligned neutrons with deformation-coupled bandhead?

Abstract A sideband in 170 Yb has been identified up to I π =17 − . It has an isomeric I =4 bandhead, yet the odd-spin states have prompt branches to the ground-state band. The contrasting properties are explained by the Coriolis effects on the quasi-particle configuration.

High-spin levels in /sup 191/Pt and /sup 193/Pt and the triaxial rotor model

The high-spin level structures of the transitional nuclei /sup 191/Pt and /sup 193/Pt have been studied by (..cap alpha..,3n..gamma..) reactions on enriched Os targets. The measurements included ..gamma..-ray singles, comprehensive ..gamma..-..gamma.. coincidences, half-life determinations, and ..gamma..-ray angular distributions. The extensive /sup 191/Pt and /sup 193/Pt level schemes established are reported here. In both nuclei, decoupled ..nu..i/sub 13///sub 2/ /sup -1/ bands, strongly resembling the ground bands of the adjacent core nuclei, and many other high-spin positive parity states have been located. Low-lying 21/2/sup -/ bands have also been observed in both nuclei and they are described as semidecoupled bands with microscopic structures dominated by three-quasiparticle components of the type (..nu..i/sub 13///sub 2/ /sup -2/,..nu..j/sup -1/). The abundant information about ..nu..i/sub 13///sub 2/ level families obtained in these experiments and in a complementary /sup 191/Au decay study is discussed, and it is shown that these complex level spectra can be accounted for rather well in terms of the coupling of an i/sub 13///sub 2/ neutron hole to a triaxially deformed core. (AIP)

The level structure of 191Pt from the decay of 3.2 h 191Au

Abstract Levels of 191Pt populated in the decay of 3.2 h 191Au have been investigated by γ-ray singles and comprehensive γ-γ coincidence measurements. A detailed 191Au decay scheme, which differs radically from earlier versions, has been established. The 191Au decay results are discussed with reference to those obtained in complementary (α, 3nγ) studies of odd-A Pt nuclei and with particular emphasis on the locations and properties of low-spin members of the ν i 13 2 level family in 191Pt.