T=1states inRb74and theirKr74analogs

Abstract

Charge symmetry breaking effects that perturb analog symmetry between nuclei are usually small but are important in extracting reliable Fermi matrix elements from ``superallowed'' \ensuremath{\beta} decays and testing conserved vector current theory, especially for the heavier cases. We have used the $^{40}\mathrm{Ca}$($^{36}\mathrm{Ar}$, $\mathit{pn}$)$^{74}\mathrm{Rb}$ and $^{40}\mathrm{Ca}$($^{40}\mathrm{Ca}$,$\ensuremath{\alpha}\mathit{pn}$)$^{74}\mathrm{Rb}$ reactions at 108, 123 and 160 MeV, respectively, to populate $^{74}\mathrm{Rb}$ and determine the analog distortion through comparison of $T=1$ states in $^{74}\mathrm{Rb}$ with their corresponding $^{74}\mathrm{Kr}$ levels. We have traced the analogs of the $^{74}\mathrm{Kr}$ ground-state band in $^{74}\mathrm{Rb}$ to a candidate spin $J=8$ state and determined the Coulomb energy differences. They are small and positive and increase smoothly with spin. New $T=0$ states were found that better delineate the deformed band structure and clarify the steps in deexcitation from high spin. A new $T=0$ band was found. No evidence was found for \ensuremath{\gamma} decay to or from a low-lying ${J}^{\ensuremath{\pi}}={0}^{+}$ state in $^{74}\mathrm{Rb}$ despite a careful search.