Isospin Conservation andβ−γCircular-Polarization Correlation in Mixed Transitions

Abstract

Measurements have been made of the $\beta -\gamma$ circular-polarization correlation parameter $A$ in the $\beta$ decays of ${\mathrm{Na}}^{22}$, ${\mathrm{Co}}^{60}$, ${\mathrm{Na}}^{24}$, ${\mathrm{Ar}}^{41}$, ${\mathrm{Sc}}^{44}$, ${\mathrm{Sc}}^{46}$, and ${\mathrm{Mn}}^{52}$. Of these seven radioisotopes the first two are pure Gamow-Teller ($\Delta J=1\mathrm{}$) transitions and therefore are expected to have values of $A=+\frac{1}{3} \mathrm{and} -\frac{1}{3}$, respectively. This expectation is well verified in the present work (in conformity with previous findings), and hence the use of these sources as standards to compare with the remaining five cases is justified. The other five nuclides involve mixed transitions ($\Delta J=0, J\ne 0$) and may therefore exhibit Fermi contributions to the extent that isospin conservation, which requires $\Delta T=1\mathrm{}$, is violated. The experimental technique used here was the now standard one of scattering the $\gamma$ rays from a cylinder of magnetized iron and then measuring the coincidence rate between $\beta$ rays and $\gamma$ rays as a function of the direction of magnetization. An added feature of the present method was the data sampling technique (rapid alternation) wherein the magnetic field direction was reversed every 8 sec in order to obviate the effects of instrumental instabilities. Such effects are of paramount importance in this experiment because the quantities measured differ by less than 1%.