Interplay of quasiparticle and phonon excitations in 181Hf observed through (n,γ) and (d→,p) reactions

doi:10.1016/S0375-9474(02)00646-2

Nuclear Physics A

Volume 709, Issues 1–4, 21 October 2002, Pages 3-59

https://doi.org/10.1016/S0375-9474(02)00646-2 Get rights and content

Abstract

Nuclear levels of ¹⁸¹Hf were investigated in the range up to 3 MeV excitation energy by (n,γ) and (d,p) reactions. Over 170 levels and about 390 γ-transitions were established most of them for the first time. 25 rotational bands were identified. Comparison of the results of the two reactions yields information on the fine structure in the fragmentation of Nilsson strength. The states below 2 MeV with the most complete spectroscopic information were interpreted in terms of the Quasiparticle Phonon Model (QPM). Excitation energies, electromagnetic transition rates, γ-branchings and spectroscopic factors are discussed in connection with their possible structure.

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Nuclear levels of 183W studied with (n,γ) and (d,p) reactions
2011, Nuclear Physics A
The level structure of ¹⁸³W has been studied using gamma–gamma coincidences from thermal neutron capture in ¹⁸²W accompanied with the reaction $(\vec{d}, p)$ . From these data and those of previous studies a total of 76 levels and about 490 connecting γ-transitions have been established for energies below 2.4 MeV. An analysis based on the standard distorted-wave Born approximation (DWBA) provides the lj-angular momentum transfers and spectroscopic factors for 36 levels up to 2.2 MeV excitation energy. A large number of particle transitions indicate an influence of strong mixing between particle and probably hole states. The extra exchange of phonons across the Fermi surface leads to a fine structure in the fragmentation of most single particle strengths and at the same time has the effect of breakdown of the individual properties of Nilsson states. The extracted $l = 1$ and 2 (d, p) sum below 2 MeV has about the same magnitude as in ^185,187W. It comprises a rather small fraction of the expected strengths. The observed states below 2 MeV are compared with predictions of the quasiparticle–phonon model. Of particular interest is the identification of “quasi-bands” with inverse spin sequence based on the state $9 / 2^{+}$ at 622.8 keV; this indicates some transition aspects from rigid rotors of light W to γ-soft nuclei in the Os-Pt region.
Nuclear structure of 187W studied with (n, γ) and (d, p) reactions
2008, Nuclear Physics A
The level structure of ¹⁸⁷W has been studied using prompt and delayed gamma–gamma coincidences from thermal neutron capture in ¹⁸⁶W and also measuring the $(d, p)$ reaction. From these data and those of previous studies a total of 170 levels (121 connected by γ transitions) have been established for energies below 2.35 MeV. Some of these levels have been grouped into rotational bands built on 14 intrinsic states of quasi-particle and quasi-particle plus phonon character. Of particular interest has been the identification of “quasi bands” with inverse spin sequence based on the newly established isomeric $11 / 2^{+}$ state at 410.1 keV. Although the DWBA analysis permitted definite spin–parity assignments for most states a large number of particle transitions have “anomalous” angular distribution shapes with respect to the DWBA which indicate an influence of strong mixing between particle and probably hole states. The exchange of phonons across the Fermi surface leads to a fine structure in the extra fragmentation of most single particle strengths and, at the same time, it produces the effect of breakdown of individual properties of Nilsson states. The total extracted $l = 1$ , 2 and 3 $(d, p)$ strengths below 2 MeV have about the same magnitudes as in ¹⁸⁵W that comprise a rather small fraction of the expected strengths. The observed states below 2 MeV are compared with predictions of the quasi particle phonon model. The discussion focuses on transition aspects from rigid rotors of light W to γ-soft nuclei in the Os, Pt region.
Low-spin mixed particle-hole structures in 185W
2005, Nuclear Physics A
The level structure of ¹⁸⁵W has been studied using the prompt and delayed gamma–gamma coincidences from thermal neutron capture in ¹⁸⁴W accompanied with the one-nucleon transfer reactions $(d, p)$ and $(d, t)$ with polarized beams. From these data and those of previous studies a total of 183 levels has been established for energies below 3 MeV. Many of these states have been grouped into rotational bands built on 28 intrinsic states of quasiparticle and quasiparticle-plus-phonon character. Although the DWBA analysis permitted definite spin–parity assignments for most of states a large number of particle transitions have ‘anomalous’ angular and asymmetry shapes with respect to the DWBA which indicate an influence of strong mixing between particle and hole states. The extra exchange of phonons and the significance of configurational $Δ N = \pm 2$ mixing across the Fermi surface lead to a fine structure in the fragmentation of most single-particle strengths and at the same time has the effect of breakdown of the individual properties of Nilsson states. The accumulated $l = 1$ $(d, p)$ sum is about a factor two smaller than the equivalent $(d, t)$ strength. Thus, the previously observed loss of the $(d, p)$ strength in the W nuclei with $A = 184, 185$ is presumably because of their redistribution amongst particle- and hole-type states. The observed states below 2 MeV are compared with predictions of the quasiparticle–phonon nuclear model.
Nuclear data sheets for A = 181
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The nuclear structure and the decay data for all the isobars of A = 181 are presented in this evaluation. New levels of ¹⁸¹Hf were studied by (n,γ), (pol d, p), (d, pγ) and (²³⁸U,²³⁷U'γ) reactions. New levels of ¹⁸¹Ta were studied by (p,nγ), (p, d), Coulomb excitation and heavy ion reactions. Heavy ion reactions added information to high spin states of ¹⁸¹Re, ¹⁸¹Os and ¹⁸¹Ir. In addition, ¹⁸¹Hg and ¹⁸¹Tl structures are also studied by α–decay experiments. The present evaluation supersedes the earlier one on A = 181 by R.B. Firestone (1991Fi01), published in Nuclear Data Sheets 62, 101 (1991), and the ones on ¹⁸¹Pt, ¹⁸¹Au and ¹⁸¹Hg, by C.M. Baglin, published in Nuclear Data Sheets 87, 197 (1999), 87, 225 (1999) and 87, 239 (1999).
January 2002 through December 2002
2003, Nuclear Data Sheets

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Nuclear Physics A

Abstract

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Radioactive nuclei from cosmochronology to habitability

Nuclear levels of <sup>183</sup>W studied with (n,<sup>γ</sup>) and (d,p) reactions

Nuclear structure of <sup>187</sup>W studied with (n, γ) and (d, p) reactions

Low-spin mixed particle-hole structures in <sup>185</sup>W

Nuclear data sheets for A = 181

January 2002 through December 2002