New Measurements ofβ-Circularly-PolarizedγAngular-Correlation Asymmetry Parameters in AllowedβDecay

Abstract

The angular-correlation asymmetry parameter for circularly polarized $\gamma$ rays following allowed $\beta$ decay has been measured for several nuclides. The polarimeter employed the usual forward Compton scattering of $\gamma$ rays, but the magnetic field direction was reversed every 7 msec (70 cps). Beta, gamma, and coincidence rates with the magnetic field off, and the single-detector $\beta$ and $\gamma$ rates during all measurements (field on), show that spurious instrumental effects are an order of magnitude smaller than the statistical errors in these measurements. Details of the calibration procedure, which utilized ${\mathrm{Co}}^{60}$ and was checked with ${\mathrm{Na}}^{22}$ and ${\mathrm{Mn}}^{56}$, and of the corrections for several spurious effects are given. The measured asymmetry parameters A, and the isotopic-spin impurity coefficients $\alpha$ which can account for the Fermi component in the mixed $\beta$ decays, are as follows: