Magnetic Moment and Beta Decay of RaE

Abstract

A.-symmetry of the beta-ray angular distribution in polarized RaE is evaluated with the numerical values of nuclear matrix elements, if r, fa and J q X r, which are , derived by the method of the least chi-square fit to the experimental data on the spectral shap'e, longitudinal polarization and jt value. . The magnetic moment of RaE is known to have a negative sign from this calculation, the measured asymmetry in Tokyo and the knowledge about the internal magnetic field at decaying nucleus. A consistent explanation of i J r, f q X r and the magnetic moment of RaE is obtained in a shell model, where the tensor forces in the residual interaction and the core po­ amples which have been studied repeatedly in con~ection with nature of weak interactions as well as nuclear structure of relevant nuclei. In this decay, the spectral shape of emitted beta rays is considerably different from the simple statistical spectrul? predicted by the Fermi theory, and it is strongly energy dependent. As is well known, this is due to the cancellation among con­ tributions of several nuclear matrix elements of the first forbidden transition; This property has been applied to examine different kinds of theoretical assumptions. Leaving a review of these problems elsewhere)!> we study here a possible way of finding the sign of the magnetic moment for RaE. For this purpose, we have to measure the beta,ray angular distribution in polarized RaE and to find nuclear matrix elements of beta decays from complete ex­ periments. In connection with these quantities, nuclear structure of RaE and RaF is investigated in a shell mo<;lel. We first describe qualitatively how we can find the sign of the magnetic · . moment by measuring the angular distribution of beta rays in polarized nuclei, and- an experimental evidence is introduced in § 2. Exact values of the asymmetry of beta-ray angular distribution are predicted by using the nuclear matrix elements, .. which are derived from the least chi-square fit to the experi­ mental data on the beta-ray spectrum, longitudinal polarization and ft value,