High-spin states inK39fromMg24(O18,p2nγγ⋯)K39

Abstract

The electromagnetic decays of several high-spin states in ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ were studied via heavy-ion-induced reactions involving ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ bombardments of targets of ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{26}{}_{}{}^{}\mathrm{Mg}$, and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$. The ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ states were formed most strongly in the ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}({}_{}{}^{18}{}_{}{}^{}\mathrm{O},p2n\gamma \gamma \cdots ){}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ reaction which provided the main body of quantitative evidence we report. The identification of specific transitions in ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$, and the resultant decay scheme, are based on Ge(Li) $\gamma -\gamma$ coincidence spectra and also on $\gamma$-ray yield curves measured for $20\le E_B\le 61$ MeV. Lifetimes of ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ states were measured by the recoil distance method. These lifetimes together with $\gamma$-ray angular distributions restrict the allowable spin-parity assignments and multipole mixing ratios for the transitions studied. Arguments based on the proposed reaction mechanism are invoked to give a most probable decay scheme for the high-spin states involved. The resulting data provide new information on the high-spin structure of ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ and also illustrate the power of these heavy-ion-induced compound-nucleus reactions as spectroscopic tools for the investigation of high-spin states in light nuclei.