Large Low-Energy M1 Strength for Fe56,57 within the Nuclear Shell Model

B. Alex Brown and A. C. Larsen
Phys. Rev. Lett. 113, 252502 – Published 19 December 2014

Abstract

A strong enhancement at low γ-ray energies has recently been discovered in the γ-ray strength function of Fe56,57. In this work, we have for the first time obtained theoretical γ decay spectra for states up to 8MeV in excitation for Fe56,57. We find large B(M1) values for low γ-ray energies that provide an explanation for the experimental observations. The role of mixed E2 transitions for the low-energy enhancement is addressed theoretically for the first time, and it is found that they contribute a rather small fraction. Our calculations clearly show that the high-(=f) diagonal terms are most important for the strong low-energy M1 transitions. As such types of 0ω transitions are expected for all nuclei, our results indicate that a low-energy M1 enhancement should be present throughout the nuclear chart. This could have far-reaching consequences for our understanding of the M1 strength function at high excitation energies, with profound implications for astrophysical reaction rates.

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  • Received 11 September 2014

DOI:https://doi.org/10.1103/PhysRevLett.113.252502

© 2014 American Physical Society

Authors & Affiliations

B. Alex Brown1,* and A. C. Larsen2,†

  • 1National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824-1321, USA
  • 2Department of Physics, University of Oslo, N-0316 Oslo, Norway

  • *brown@nscl.msu.edu
  • a.c.larsen@fys.uio.no

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Issue

Vol. 113, Iss. 25 — 19 December 2014

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