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Properties of Excited States of P31. II. Gamma-Ray Angular Distributions and Correlations

Gale I. Harris

L. W. Seagondollar

  • Aeronautical Research Laboratories, Wright-Patterson Air Force Base, Ohio

  • Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas

Phys. Rev. 131, 787 – Published 15 July, 1963

DOI: https://doi.org/10.1103/PhysRev.131.787

Abstract

Angular distributions and triple correlations of gamma rays emitted from several resonances in the range Ep=1177 to 1509 keV in the Si30(p, γ)P31 reaction have been measured using thin, highly enriched Si30 targets. The decay schemes of these resonances and of intermediate levels excited in P31 were presented in an earlier paper (I). The angular distributions and correlations lead to the resonance level assignments 1177(72), 1204(52), 1324(52), 1392(52), 1400(32), 1489(32), and 1509(52) where the proton resonance energies are in keV. The results indicate even parity for all of the resonances if it is assumed that all gamma-ray multipolarity mixings are of the form E(L+1)M(L). The mixing ratios (all of the type E2M1) are presented for most of the observed primary transitions and of several secondary transitions. The results of this study are consistent with the assignments 32+, 52+, 32+, 52+, 32+, and 52+ made elsewhere for the 1.27-, 2.23-, 3.13-, 3.29-, 3.51-, and 4.19-MeV levels of P31. The 3.41-MeV level is identified as 72+ by means of angular-distribution and correlation measurements at the 1509-keV resonance. A 72+ assignment for the 3.41-MeV level casts doubt upon the existence of a weak transition, which has been reported by earlier workers and in I, from that level to the ½+ ground state. Results of several measurements designed to determine the origin of the weak gamma-ray peak of approximately 3.4 MeV in coincidence spectra at the 1509-keV resonance were inconclusive. Angular distributions at the 1204-keV resonance lead to the assignment of 32+ to the 4.26-MeV level. Limitations are placed on the possible assignments for the 4.43- and 5.01-MeV levels. Both members of the recently discovered doublet near Ep=1481 keV are found to decay mainly to the ground state, and each have J=32 on the basis of angular distributions. The value of ΓpΓγΓt has been determined for each of the resonances. Results of this study are discussed in terms of recent collective model calculations for P31.

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