Spectral shapes and a beta-gamma directional correlation in the beta decay of
Abstract
The isotope 172Tm populates the 0+, 2+ and 4+ states of the 172Yb ground-state rotational band directly in beta decay. The shapes and intensities of the three beta groups have been measured by means of a six-gap magnetic spectrometer operated in coincidence with a NaI(Tl) crystal. The experimental shape factor plots are taken relative to the 90Y shape factor measured in the same circumstances, and it is concluded that on this basis the shapes of all three 172Tm beta groups agree with the theoretical shape for a first-forbidden unique transition. The directional correlation for the 2−(β)2+(γ)0+ cascade has been measured at six energies from 1010 to 1550 keV and these results too are consistent with the assumption that the 2− → 2+ beta transition is purely of tensor rank 2. The data for the 2− → 2+ transition are analysed on the basis of the modified Bij approximation, which defines parameters X and Y corresponding to the relative contributions of tensor ranks 0 and 1 respectively. The shape measurement provides the limit X2+Y2 ≦ 0.10, whereas the angular correlation measurement gives Y = 1.64X+(0.02±0.03). The reduced transition probabilities can therefore be compared with the theoretical intensity rules for λ = 2, which predict the ratios 0.70 : 1 : 0.05 for the branches to the 0+, 2+ and 4+ states. The experimental result is (0.63±0.19) : 1 : (0.046±0.007).
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Cited by (13)
Nuclear data sheets for A = 90
1997, Nuclear Data SheetsExperimental data for all nuclei with mass number A = 90 have been evaluated, and their corresponding level schemes from radioactive decay and reaction studies are presented.
This evaluation shows levels in90Tc and90Ru from (HI, xpxnγ) reactions seen for the first time, and new levels up to spin J = 25 in90Mo. A new precise measurement (93Mi04) of γ rays using the89Y(n, γ) reaction provided a complete level scheme for90Y, which has superseded that of 83De27.
Cutoff Date:All data received by May 1, 1997 were evaluated.
General Policies and Organization of Material:See the January issue of Nuclear Data Sheets.
Nuclear data sheets for A = 172
1995, Nuclear Data SheetsNuclear spectroscopic data for known nuclides of mass number 172 (Ho,Er,Tm,Yb,Lu,Hf,Ta,W,Re,Os,Ir,Pt,Au) have been evaluated and presented together with adopted energies and Jπ of levels in these nuclei. No data are yet available for excited states in 172Ho, 172Pt and 172Au. This evaluation represents a revision of earlier Nuclear Data Sheets for A=172 (87Wa15,75Gr17). No experimental data are available for 172Gd, 172Dy, 172Hg, and 172Pb. Structure calculations related to deformation, moments, superdeformed shapes, and intruder levels have been reported by 84Sa16 (for 172Gd, 172Dy), 87Ne03 and 87Ne07 (for 172Dy), 93Na05 and 94Pa29 (for 172Hg) and 85He09 (for 172Pb). Recently, 95Hi02 have reported a study of the α and ϵ decay of 172Os. The authors have proposed, for the first time, a level scheme of 172Re with 9 excited states incorporating 11 γ rays. The following energy levels (γ ray) are populated in 172Os ϵ decay: 63.0+y(63.0γ); 161.4+y(98.4γ); 169.8+y(106.8γ); 185.0+y(122.0γ); 239.8+y(176.7γ,239.8γ); 274.1+y(211.1γ); 291.5+y(228.4γ,291.5γ); 360.5+y(120.7γ); 906.3+y(843.3γ). The authors list the following γ rays with energy (intensity): 63.0 3 (100), 98.4 4 (1), 106.8 4 (1), 120.7 4 (2), 122.0 4 (1), 159.9 4 (4 1), 176.7 2 (40 6), 211.1 4 (2), 226.1 5 (2), 228.4 4 (2), 239.8 2 (37 7), 291.5 3 (5.5 12), 843.3 10 (4 2), 1120.1 15 (15 10). Levels populated are stated in adapted levels, gammas. Consult ENSDF for 172Re for details.
Nuclear data sheets for A = 172
1987, Nuclear Data SheetsExperimental nuclear structure and decay data pertaining to all nuclei with mass number A=172 have been compiled and evaluated. Level schemes from both radioactive decay and reaction studies are presented, along with associated tables of experimental data and adopted properties for levels and transitions. This work supersedes the previous evaluation by L. R. Greenwood (75Gr17) published in Nuclear Data Sheets 15, 497 (1975).
Nuclear Data Sheets for A = 90
1975, Nuclear Data SheetsThe 1961 version of Nuclear Data Sheets for A=90and the 1970 Midstream Evaluation, A=90+J. B. Ball, M. W. Johns, and K. Way, Nuclear Data Tables8, 407 (1970)+, have been revised on the basis of experimental data received prior to May 1, 1975. Results from approximately 225 papers and communications chosen from the extensive literature for this A-chain have been included in the present evaluation. Numerous additional references dealing with reaction mechanism studies and nuclear structure theory are not included in this compilation, but are available upon request from the Nuclear Data Project.
Data on nine A=90 nuclei are presented. The decay of 90Br has been observed, but the decay scheme has not been established. Recent unpublished results on 90Kr and 90Rb decays are presented. These results are not yet comlete, but appear to be considerably more extensive than previously published work. The particularly simple decay schemes for 90Sr and 90Y are wellk known. A few spin assignments have been proposed for levels in 90Sr, but additional reaction studies would be useful. Many spin assignments have been made for levels in 90Y, 90Zr, 90Nb, and 90Mo from a variety of decay and reaction studies. The results for 90Zr are particularly extensive. The decay schemes for 90Nb and 90Mo appear reasonably well established. Recent results on the decay of two 90Tc isomers are presented, but the decay schemes have not been established and the energy ordering of the two isomers is not known.
Decay of <sup>172</sup>Tm: The mixing of K<sup>π</sup> = 0<sup>+</sup> and 2<sup>+</sup> bands in <sup>172</sup>Yb
1974, Nuclear Physics, Section AThe level scheme of 172Yb has been studied from the decay of 63.6 h 172Tm. Gamma-ray energy and intensity measurements were made using Ge(Li) spectrometers. Forty-eight γ-ray transitions, nine of them previously unreported, are observed. All of these have been incorporated into a 172Yb level scheme consisting of 16 excited states. The previously reported “1119 keV” γ-ray is shown to be a doublet, with one member de-exciting the I, Kπ = 2, 0+ state at 1117.8 keV and the other de-exciting the I, Kπ = 2, 1− octupole-vibrational state at 1198.5 keV. This observation, together with that of the additional γ-ray transitions, provides further information on the de-excitation of the 172Yb levels. Attention is focused on the properties of the excited Kπ = 0+ bands at 1042 and 1404 keV and the Kπ = 2+ bands at 1465 and 1608 keV. A phenomenological five-band mixing analysis of the γ-ray branching-ratio data, involving these four bands and the ground-state band, has been carried out. Results of this analysis are presented for two different assumptions concerning the signs of certain of the matrix elements coupling the excited bands. Additional measurements which could help in choosing between these two alternatives are indicated. Interesting similarities in some of the properties of the two excited 2+ bands are pointed out, and a qualitative explanation of them is given in terms of the Nilsson level diagram relevant to 172Yb.
Hindrance factors for unique first-forbidden beta transitions in deformed nuclei
1970, Nuclear Physics, Section AThe absolute transition probabilities for first-forbidden unique beta transitions in 159Dy, 169Er and 185W have been measured. These values along with the earlier reported values for 166Ho and 172Tm have been compared with the theoretical transition probabilities calculated from the Nilsson model with pairing corrections included. On this scale the observed transitions are hindered by the following factors: 159Dy 3.2, 166Ho 1.4, 169Er 0.9, 172Tm 10.9, and 185W 2.5.