Fermi nuclear matrix element of allowed isospin-hindered positron decay of Co56

Abstract

The experimental measurement of the asymmetry parameter of the + decay from the 4+ ground state of Co56 to the 2.085 MeV 4+ state of Fe56 not only yields a value for the Fermi nuclear matrix element MF, but also has significant Fermi-Gamow-Teller mixing and is of interest for a time-reversal invariance test of the weak interaction. To date, nine such measurements have been made and the values of the MF fall into two groups: MF10-5 and MF(35)×10-4. Our theoretical calculation using the Nilsson model and a one-body spheroidal Coulomb potential yields MF=2.3×10-4 for =0.1 and MF=6×10-4 for =0.2, which are in reasonable agreement with the experimental values of MF(35)×10-4. © 1988 The American Physical Society.