Isospin Purity and Delayed-Proton Decay:Ne17andAr33

Abstract

$\ensuremath{\beta}$-delayed proton and $\ensuremath{\gamma}$-ray measurements have been used to study the decay of $^{17}\mathrm{Ne}$ and $^{33}\mathrm{Ar}$. Their half-lives have been measured as 109.0 \ifmmode\pm\else\textpm\fi{} 1.0 and 173.0 \ifmmode\pm\else\textpm\fi{} 2.0 msec, respectively, and absolute $\mathrm{ft}$ values have been determined for their $\ensuremath{\beta}$-decay branches. Precise level energies have been measured in $^{17}\mathrm{F}$ and $^{33}\mathrm{Cl}$, and an earlier discrepancy concerning energies in $^{17}\mathrm{F}$ has been resolved. The $log\mathrm{ft}$ value for the superallowed decay branch of $^{17}\mathrm{Ne}$ has been measured to be ${3.29}_{\ensuremath{-}0.07}^{+0.04}$, which indicates an isospin purity of \ensuremath{\ge}95% for the lowest $T=\frac{3}{2}$ state in $^{17}\mathrm{F}$. In addition, the antianalog configuration is located in $^{17}\mathrm{F}$ and is shown to be the most probable source of the small isospin mixing present in the analog state in that nucleus. The $log\mathrm{ft}$ value measured for the superallowed decay branch from $^{33}\mathrm{Ar}$ was 3.34 \ifmmode\pm\else\textpm\fi{} 0.05, a value which suggests an impurity of \ensuremath{\sim}10% in the lowest $T=\frac{3}{2}$ state in $^{33}\mathrm{Cl}$. There is circumstantial evidence that this mixing occurs with four $T=\frac{1}{2}$ states which lie within 350 keV of the analog state.