Circular Polarization Measurements in the β Decay of V48, Co56, Fe59, and Cs134

Abstract

The $\beta -\gamma$ circular-polarization angular correlation has been measured for ${\mathrm{V}}^{48}$, ${\mathrm{Co}}^{56}$, ${\mathrm{Fe}}^{59}$, and ${\mathrm{Cs}}^{134}$ using the Livermore apparatus described previously. Since all of these decays (with one exception) are characterized by $\Delta J=0\mathrm{}$, $J\ne 0$, and $\Delta T\approx 1$, they possess the necessary elements for testing isospin conservation in allowed $\beta$ decay. The measured asymmetry parameters are: -0.066±0.035 for ${\mathrm{V}}^{48}$, 0.00±0.03 for ${\mathrm{Co}}^{56}$, -0.074±0.022 for ${\mathrm{Cs}}^{134}$, and -0.23±0.05 and 0.01±0.10, respectively, for the 462-keV and 271-keV, $\beta$ branches in ${\mathrm{Fe}}^{59}$. These results are consistent in all cases with a very small Fermi matrix element and therefore support the validity of isospin conservation, with the doubtful exception of the 271-keV $\beta$-decay branch of ${\mathrm{Fe}}^{59}$. However, in this case the extreme difficulty of disentangling the 271-keV branch from the 462-keV branch, which is pure Gamow-Teller [$\frac{3}{2^{-}}\left(\beta \right)\frac{5}{2^{-}}\left(\gamma \right)\frac{7}{2^{-}}$], renders this exception rather uncertain. In the case of ${\mathrm{V}}^{48}$ our result is in disagreement with that of Boehm and Wapstra, who found evidence for sizable interference, but is in better agreement with the result of Daniel and Kuntze, who find evidence for small interference. Our ${\mathrm{Co}}^{56}$ result is in excellent agreement with the work of Daniel and Kuntze. Our result for the low-energy branch of the ${\mathrm{Fe}}^{59}$ decay ($\Delta J=0\mathrm{}$) is in accord with the work of Forster and Sanders, the accuracy being, however, very poor in both measurements. With regard to the high-energy branch ($\Delta J=1\mathrm{}$), our result is lower by a factor of two than that of Forster and Sanders.