Weak branches in 42Sc, 35Ar, and 27Si beta + decay.

Abstract

The weak nonanalog Fermi branch to the 1.837 MeV level of $^{42}\mathrm{Ca}$ and several weak branches in $^{35}\mathrm{Ar}$ and $^{27}\mathrm{Si}$ ${\ensuremath{\beta}}^{+}$ decay have been remeasured in order to reduce statistical uncertainties and reconcile discrepancies in the literature. The weak branches were detected by measuring subsequent cascade gamma rays with a Ge detector surrounded by a NaI anti-Compton shield. Fast transport of thin, self-supporting targets was provided by a magnetically driven rabbit system. For $^{42}\mathrm{Sc}$ the ratio of the weak branch relative to the superallowed ground state to ground state transition was found to have a value of (7.0\ifmmode\pm\else\textpm\fi{}1.2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$. This value is in good agreement with two of the three earlier, less precise, measurements. It is at the low end of theoretical estimates. The new results for the weak branches in $^{35}\mathrm{Ar}$ and $^{27}\mathrm{Si}$ have reduced uncertainties and agree well with a previous determination.