Identification of spin relaxation following α-decay in odd-A nuclei

Abstract

A novel graphical method has been devised for decay, in odd-A nuclei, when JP < J1, to determine whether spin relaxation in the state of spin J1 has occurred. For a short lived excited daughter state A* of spin J1, its populated magnetic substates, following α-decay from a parent nucleus [A + 4] of spin JP, should be restricted to those of value |M| ⩽ JP (when J1 > JP). However, for longer lived excited states, spin relaxation allows population of JP < |M| ⩽ J1 substates. The statistical tensors B2 and B4 (or population alignment coefficients) of Rose and Brink can be determined from the measured (non-zero) Legendre polynomial coefficients. These measured B2 and B4 can be compared with their theoretical counterparts both for the case when |M| ⩽ JP and for the case when |M| ⩽ J1. It is then readily apparent, from a graphical examination, whether spin relaxation has occurred or not. The same statistical tensors B2 and B4, also allow one to analyse α–γ directional angular correlations and α–γ linear polarization angular distributions simultaneously, rather than as different data sets. The technique has been applied to the case of decay. Spin relaxation of the 271 keV state allowing population of substates with |M| ≤ 7/2, is required to satisfactorily fit the published data. The population of the M = ±7/2 substates due to spin relaxation is estimated to be less than 20% of the total, equally split between the two.