Proton capture to excited states of O16: M1, E1, and Gamow-Teller transitions and shell model calculations

K. A. Snover, E. G. Adelberger, P. G. Ikossi, and B. A. Brown
Phys. Rev. C 27, 1837 – Published 1 May 1983
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Abstract

We have measured excitation functions of the γ rays resulting from the bombardment of N15 by polarized and unpolarized protons in the energy range Ep=2.59.5 MeV with emphasis on identifying dipole decays to the first (0+) and second (3) excited states in O16. Resonances in γ12 are observed at Ex=16.21, 16.45, 16.82, 17.12, 18.03, 18.98, 19.90, and 20.41 MeV. The 16.21 and 17.12 MeV resonances in γ12 are identified as M1 decays of the 1+ T=1 states to the 6.05 MeV 0+ state in O16. The measured ratio of reduced strengths B(M1, γ1)B(M1, γ0) is 0.48±0.03 for decays from the 16.21 MeV state and 0.55±0.04 for decays from the 17.12 MeV state. The 18.03 MeV resonance is due to a 3 T=1 state in O16 with a strength ΓpΓγ2Γ=(1.96±0.27) eV and the 18.98 MeV resonance is due to the 4 T=1 stretched particle-hole state with a strength of (0.85±0.10) eV. We determine absolute particle and γ widths for these states. The M1 γ2 width of the 18.98 MeV state, (7.1±3.1) eV, is in agreement with a shell-model calculation. Resonances in γ3 are observed at 16.82 and 17.27 MeV and in γ4 at 17.88 MeV. The excitation energies and widths of these levels as well as the strengths of the γ transitions suggest a T=1 character for all of the resonances for which capture γ rays are observed. Correspondences of our resonances to levels in N16 are given. Strong α1 branches for many of these states indicate isospin impurities. We compare γ widths, including ground-state M1 decays, and allowed β transition rates in A=16 nuclei with shell model calculations and obtain rough agreement with the experimental results. Additional shell model calculations for M1 and Gamow-Teller decays in the A=14, 15, 17, and 18 nuclei are presented, which indicate that Gamow-Teller matrix elements are quenched by ∼20% relative to shell model predictions and also relative to the spin part of the M1 matrix elements.

NUCLEAR REACTIONS N15(p, γ)O16, N15(p, pγ)N15, N15(p, α1γ)C12, E=2.59.5 MeV, measured capture γ rays to Ex=6.05, 6.13, 6.92, and 7.12 MeV final states. Measured σ(90°), Ay(90°), σ(θ). Deduced M1 and E1 resonance strengths. Performed shell model calculations and compared with these and other M1 and Gamow-Teller strengths in nuclei near A=16. Deduced average inhibition of GT matrix elements relative to shell model and to the spin part of M1 matrix elements.

  • Received 25 January 1983

DOI:https://doi.org/10.1103/PhysRevC.27.1837

©1983 American Physical Society

Authors & Affiliations

K. A. Snover and E. G. Adelberger

  • Nuclear Physics Laboratory, University of Washington, Seattle, Washington 98195 and Nuclear Physics Laboratory, Oxford University, Oxford OX1 3RH, England

P. G. Ikossi

  • Nuclear Physics Laboratory, University of Washington, Seattle, Washington 98195

B. A. Brown

  • Nuclear Physics Laboratory, Oxford University, Oxford OX1 3RH, England and Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824

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Vol. 27, Iss. 5 — May 1983

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