The retarded transitions in 181Ta and 175Lu and the effective magnetic moment operator

doi:10.1016/0375-9474(69)90448-5

Nuclear Physics A

Volume 133, Issue 1, 11 August 1969, Pages 50-64

https://doi.org/10.1016/0375-9474(69)90448-5 Get rights and content

Abstract

The retarded transitions assigned as $52, 52^{+} [402]→ 72, 72^{+} [404]$ in ¹⁸¹Ta (482 keV) and ¹⁷⁵Lu (343 keV) are analysed with special regard to the large hindrance of the M1 radiation in ¹⁸¹Ta. The E2 component is dominated by the band mixing which is thus determined by B(E2). For the analysis of B(M1), we exploit the relation between the Coriolis and M1 intrinsic matrix elements. The result shows a marked difference between ¹⁸¹Ta and ¹⁷⁵Lu. Calculations with extended models for particle motion indicate possible effects of the detailed deformation structure for the two cases. Furthermore, the predicted tensor term k₂[Y², s]¹ in the μ operator gives a significant contribution to B(M1), when k₂ is of the order of unity. The present data are consistent with the condition k₂ ⪅ 0.6, whereas $k_{2} ⪆ is 0$ preferred because of consistency with the model calculations.

The effective magnetic moment operator can be written in the form $μ ≈ (g_{l}^{0} + δg_{l}^{ex}) l +(g_{s}^{0} +δg_{s}^{pol} +δg_{s}^{ex}) s +(k_{2}^{pol} +k_{2}^{ex})[Y^{2}, s]^{1}$ , where g_l⁰ and g_s⁰ are the unrenormalized nucleon g-factors. The term δg_s^pol represents the well-known g_s renormalization due to spin polarization (δg_s^ex is small). We have estimated the pion-exchange contributions, giving τ₃g_l^ex ≈ 0.1 and τ₃k₂^ex ≈ − 1. When our preferred range for k₂ from the present analysis is combined with previous data from other work, we can give the conservative semiempirical estimate 0 < τ₃k₂^pol ⪅ 2.5 for the spin polarization contribution when this is assumed to have isovector character.

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The reduced probabilities of M3 transitions are studied in five deformed and three spherical or near-spherical odd-mass nuclei. In deformed nuclei, the states linked by M3 transitions are predominantly of single-quasiparticle nature and the calculations are performed taking into account the single-quasiparticle as well as core-polarization terms in the M3-operator. Whereas in ¹⁵⁹Ho, ¹⁷⁵Yb, and ¹⁷⁹Hf the ratio between theoretical and experimental B(M3) values range from 0.5 to 1.4, the situation is much worse in neutron deficient nuclides ¹⁷⁹W and ¹⁸³Pt where the theory used can not explain a very sharp drop of the B(M3) values. In the soft nuclei ¹²¹Cs and ²⁰⁷Po the states connected by M3 transitions are treated as “quasiparticle⊗phonon” states. In ¹¹³Sn, the small “quasiparticle⊗phonon” components are not sufficient to compensate vanishing contribution of the dominant quasiparticle component, which shares Δℓ forbidden transitions. Thus, on the whole theoretical description of B(M3) with the present simple models seems to be unsatisfactory. It constitutes a challenging problem both at the level of the nuclear structure and the transition operator.
Isomeric M3 transitions in 183Pt and 181Os
1998, Nuclear Physics A
The M3 transitions linking the $ν 72 [514]$ and $ν 12 [521]$ states in ₇₈¹⁸³Pt₁₀₅ and ₇₆¹⁸¹Os₁₀₅ have been searched by high-resolution conversion-electron measurements. The reduced M3 transition probabilities have been estimated and compared to the values obtained in neighbouring isotones (₇₄¹⁷⁹W₁₀₅ and ₇₉¹⁸⁴Au₁₀₅). All the known M3 transitions are presented and their properties discussed, especially as a function of deformation. The present work supports the $π h 92 ⊗ν 12 [521]$ and $π h 92 ⊗ν 72 [514]$ particle configuration assignments proposed for the ¹⁸⁴Au isomeric and ground states, respectively.
Evidence for abnormal M1 transition in 187Pt
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Gamma-gamma angular correlation measurements have been performed in ¹⁸⁷Pt in order to determine the spin values of the states connected by the highly converted transitions. For one of these transitions, we have determined that the spin values of the initial and final states are different, which implies abnormal M1 multipolarity for this highly converted transition. In that case the deduced penetration parameters have especially high absolute values. Moreover we have determined uniquely the spin value of most of the excited states below 800 keV. The occurence of highly converted transitions in ¹⁸⁷Pt is examined and the low-spin negative-parity levels are discussed in terms of shape coexistence.
The l-forbidden Gamow-Teller decay of 39Ca
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The intensities of γ-rays emitted following the β⁺ decays of ³⁹Ca and ³⁵Ar were measured by using a Ge(Li) detector to detect the delayed radiation from a KCl target bombarded by 13 MeV protons. From these results the experimental log $(ƒt)$ values and related B(GT) values for the ³⁵Ar and ³⁹Ca decays are deduced. These are compared with shell-model calculations together with a recent computation by Towner and Khanna of the higher-order corrections due to configuration-mixing outside the sd shell, isobar currents and other meson-exchange currents. We concentrate on the significance of the $l- forbidden 1 d_{32} → 2 s_{12}$ Gamow-Teller transition in mass 39 and comment on its relation to the corresponding M1 transitions in ³⁹Ca and ³⁹K.
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Consideration of second-order core-polarisation, isobar-current and meson-exchange-current processes gives a satisfactory understanding of the ground-state magnetic moments and mirror β-decay transition probabilities in closed-shell-plus- (or minus) one nuclei, A = 3, 15, 17, 39 and 41. Perturbation contributions from high-lying excited states (tensor correlations) from one-body and two-body meson-exchange operators cancel strongly in diagonal matrix elements, but in off-diagonal matrix elements between spin-orbit partners the cancellation is less. Similarly, with isobar currents, there is a strong cancellation between direct and exchange contributions in diagonal matrix elements, while the exchange term is suppressed in off-diagonal cases. Of the two contributions, tensor correlations are found to be as important as, if not more important than, isobar currents. The calculated lowest-order meson-exchange-current contributions to magnetic moments are close to the soft-pion limit predictions.

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^†: Present address: State University of New York at Stony Brook, Stony Brook, Long Island, N.Y., USA.

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Nuclear Physics A

Abstract

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Cited by (53)

On M3-transition rates in selected odd-mass nuclei

Isomeric M3 transitions in <sup>183</sup>Pt and <sup>181</sup>Os

Evidence for abnormal M1 transition in <sup>187</sup>Pt

The l-forbidden Gamow-Teller decay of <sup>39</sup>Ca

Nuclear magnetic properties and gamow-teller transitions

Corrections to the single-particle M1 and Gamow-Teller matrix elements