Electron Capture in the Decay ofNa22

Abstract

The ratio of electron capture to positron emission in the decay of ${\mathrm{Na}}^{22}$ to the 1.28-Mev level in ${\mathrm{Ne}}^{22}$ has been determined by a comparison of the intensities of positron emission and 1.28-Mev radiation. The measurements were made with a coincidence arrangement employing a $4\ensuremath{\pi}$ beta counter to detect the positrons and a scintillation counter for the $\ensuremath{\gamma}$ rays. By varying the bias of a discriminator responding to the $\ensuremath{\gamma}$ spectrum, one can determine the efficiency of the $4\ensuremath{\pi}$ beta counter, and the product of this efficiency and the fraction of decays which undergo electron capture. These measurements lead to a value of 0.110\ifmmode\pm\else\textpm\fi{}0.006 for the ratio of electron capture to positron emission. If one assumes that the ${\mathrm{Na}}^{22}$ decay is allowed ($\ensuremath{\Delta}J=1$, no) the theoretical value is 0.1135. By a comparison of these values, we can make an estimate of the magnitude of the Fierz interference term. We find, subject to the above assumption, that the ratio of the axial vector and tensor coupling constants $\frac{{C}_{A}}{{C}_{T}}=(\ensuremath{-}1\ifmmode\pm\else\textpm\fi{}2)$ percent.