Elsevier

Nuclear Physics A

Volume 90, Issue 1, January 1967, Pages 122-134
Nuclear Physics A

Lifetimes of levels in 21Ne

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Abstract

Attenuated Doppler shifts have been measured for the decay of the levels in 21Ne at 1.74, 2.80 and 2.87 MeV using 24 MeV 16O ions from the Harwell tandem Van de Graaff accelerator and the reaction 9Be(16O, αγ)21Ne. From these results, the mean lifetimes of the 1.74 and 2.87 MeV levels were found to be, in units of 10−13 sec, 1.5−1.0+1.5 and 1.1−0.7+1.5 respectively. The observed Doppler shift for the decay of the unresolve doublet at 2.80 MeV is consistent with the recent lifetime limits and branching ratios given by Smulders and Alexander for levels at 2.790 and 2.797 MeV. The data are combined with branching ratio and multipole mixing ratio data to obtain the partial mean lifetimes of eight transitions in 21Ne. The results are discussed in terms of the systematics of transitions in the 2s-1d shell and in terms of several nuclear models. The lifetimes and branching ratios of the 1.74 and 2.87 MeV levels are consistent with the predictions of the Nilsson model with K-band mixing for spin and parity assignments of 72+ and92+, respectively, to those two levels. The results for the 2.797 MeV level are consistent with the predictions of the Nilsson model, the Chi-Davidson asymmetric core model and the Dreizler excited core model if a 12+ spin and parity assignment is made to this level. However, the results for the 2.790 MeV level are inconsistent with its interpretation as the 52+ level predicted in this energy region by the Nilsson and Dreizler models, since these models overestimate the M1 transition probabilities for decay by several orders of magnitude and fail to give the correct branching ratio.

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  • Cited by (6)

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    • Energy levels of A = 21-44 nuclei (V)

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    • Decay and lifetimes of levels in <sup>21</sup>Ne

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    Part of this work was performed while this author was a John Simon Guggenheim Fellow (1962–1963) at Harwell, on leave from Indiana University.

    †††

    Dr. J. E. Evans died suddenly on December 17, 1965 while the manuscript for this paper was in the final stages of prepartion.

    Present address:Argonne National Laboratory, Argonne, Inninois, USA.

    ‡‡

    Present address:Department of Geology and Geophysics, the University of Oxford, England.

    ‡‡‡

    On leave 1962-63 from Southern Universities Nuclear Institute, Faure, South Africa

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