Signature-splitting systematics of the positive-parity bands in odd-N rare-earth nuclei

doi:10.1016/0375-9474(87)90001-7

Nuclear Physics A

Volume 470, Issue 2, 24 August 1987, Pages 253-265

https://doi.org/10.1016/0375-9474(87)90001-7 Get rights and content

Abstract

Experimental values of the signature-dependent splitting in energy for the N = 91–101 isotopes of erbium ytterbium, hafnium, tungsten, and osmium (Z = 68–76) are extracted for the lowest positive-parity quasineutron configurations. A correlation is established between this splitting and the relative energy of the Fermi level, λ, and that of the $Ω = 12$ component of the $i_{132}$ neutron orbital. Whereas cranking calculations based on deformations appropriate to no quasiparticle excitation underpredict the observed signature splitting, the splitting can be reproduced for N = 95–99 isotopes, when the deformation effect of exciting a positive-parity quasineutron is included.

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Nuclear Structure and Decay Data for A=167 Isobars
2023, Nuclear Data Sheets
Experimental nuclear spectroscopic data are compiled and evaluated for 17 known nuclides of mass 167 (Sm, Eu, Gd, Tb, Dy, Ho, Er Tm, Yb, Lu, Hf, Ta, W, Re, Os, Ir, Pt), 23 years after the previous full evaluation by 2000Ba65. Detailed information is presented for each reaction and decay experiment. Combining all the available data, recommended values are provided for energies, spins and parities, and half-lives of levels, with energies, branching ratios and multipolarities of γ radiations, and characteristics of β and α radiations in radioactive decays. The α decays of A=171 nuclei to A=167 daughters are included in this work, while for α decays of A=167 nuclei to A=163 daughters, consult Nuclear Data Sheets (2010Re03) or the ENSDF database for A=163. ¹⁶⁷Er, ¹⁶⁷Tm, ¹⁶⁷Yb, ¹⁶⁷Lu and ¹⁶⁷Ta are among the most extensively studied nuclides via decay and high-spin gamma-ray spectroscopy measurements, followed by ¹⁶⁷Ho, ¹⁶⁷Hf, ¹⁶⁷W, and ¹⁶⁷Os. Information for excited states in ¹⁶⁷Dy, ¹⁶⁷Re, and ¹⁶⁷Ir are limited; no excited states have yet been identified in ¹⁶⁷Sm, ¹⁶⁷Eu, ¹⁶⁷Gd, ¹⁶⁷Tb and ¹⁶⁷Pt, with the ground-state half-life of ¹⁶⁷Sm remaining unknown. This work supersedes the earlier evaluation of A=167 nuclei by 2000Ba65.
High spin spectroscopy with the projected shell model
1996, Physics Report
High-spin structure of 167W and 168W
1992, Nuclear Physics, Section A
Excited states in ¹⁶⁷W and ¹⁶⁸W, populated in the $^{142} Nd (^{30} Si, x n)$ reaction, were investigated at high spins using the ESSA30 array with 29 Compton-suppressed Ge detectors. The level schemes are extended to higher spins and several new rotational bands are identified. The results are discussed in comparison with existing data on the neighbouring N = 93 and 94 isotones and on the Z = 74W isotopes. A theoretical analysis is presented within the framework of a pairing-self-consistent cranked shell model using shape parameters obtained from total-routhian-surface calculations.
First observation of high-spin states in 167Ta and 168Ta
1992, Nuclear Physics, Section A
Excited states in ¹⁶⁷Ta and ¹⁶⁸Ta, populated in the ¹⁴²Nd(³⁰Si, pxn) reaction, were investigated using the ESSA30 array with 29 Compton-suppressed Ge detectors. Several rotational decay sequences are identified and for the first time a high-spin level scheme is established for these nuclei. The results for ¹⁶⁷Ta are discussed in comparison with existing data in the neighbouring nuclei and with cranked shell model calculations. The possible intrinsic structure and its consequences for the yrast band in ¹⁶⁸Ta are also briefly discussed.
Signature-dependent effects of gamma vibration on E2 transitions in rotating odd-A nuclei. (II). Triaxial nuclei
1990, Nuclear Physics, Section A
Signature-dependent effects of gamma vibration on properties of rotating odd-A nuclei are studied by means of the quasiparticle-vibration-coupling approach based on the cranking-plus-RPA formalism. In the first half of this paper, the signature dependence and the shell-filling dependence of both the quasiparticle-vibration-coupling wave function and of the E2 transitions in the γ = 0 case are discussed. The gamma-vibrational effect on B(E2: I → I − 2) is shown to be weaker than that on B(E2: I → − 1). In the second half, the vibrational effect on B(E2: I → I − 1) in γ ≠ 0 cases is shown to defeat the effect of the static gamma deformation of the rotating potential when γ^(pot) is smaller than the zero-point amplitude γ₀. A prediction is given for the signature and the shell-filling dependence of B(E2: I → I − 1) and for the sign change of $E2 M1$ mixing ratio in an experimentally accessible isotope chain, ^159–169Yb.
Proton band crossings and electromagnetic transition probabilities in 161Lu
1988, Nuclear Physics, Section A
Two new negative-parity and two new positive-parity decay sequences are established to high spin for ¹⁶¹Lu₉₀. The resulting systematics of the routhians, alignments, and B(M1)/B(E2) ratios indicate that ¹⁶¹Lu has both a smaller and less stable quadrupole deformation than the lighter N = 90 isotones and the heavier lutetium isotopes. At low spin, the data are consistent with a sizeable negative γ deformation. Above the band crossing associated with the excitation of a pair of $i_{32}$ quasineutrons, the evidence for γ deformation disappears; however, the configuration-dependent B(M1)/B(E2) ratios indicate that the nuclear shape may not be completely stable. The systematics of the band crossings based on the excitation of a pair of $h_{12}$ quasiprotons observed at higher spins in ¹⁶¹Lu and other odd- and even-Z, N = 90 isotones provides the first experimental evidence from high-spin data for proton quadrupole pair correlations.

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¹: On sabbatical leave from The State University of New York, Plattsburg, New York.

²: Permanent address: Kernfysisch Versneller Institut, Groningen, The Netherlands.

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Nuclear Physics A

Abstract

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Nuclear Structure and Decay Data for A=167 Isobars

High spin spectroscopy with the projected shell model

High-spin structure of <sup>167</sup>W and <sup>168</sup>W

First observation of high-spin states in <sup>167</sup>Ta and <sup>168</sup>Ta

Signature-dependent effects of gamma vibration on E2 transitions in rotating odd-A nuclei. (II). Triaxial nuclei

Proton band crossings and electromagnetic transition probabilities in <sup>161</sup>Lu