Isobaric-Analog Resonances in Se Isotopes

Isobaric-analog resonances have been observed by measuring excitation curves for ($p,p$) elastic scattering from ${}_{}{}^{76}{}_{}{}^{}\mathrm{Se}$, ${}_{}{}^{78}{}_{}{}^{}\mathrm{Se}$, ${}_{}{}^{80}{}_{}{}^{}\mathrm{Se}$, and ${}_{}{}^{82}{}_{}{}^{}\mathrm{Se}$. Excitation curves were also measured for the ($p,n$) reaction on ${}_{}{}^{78}{}_{}{}^{}\mathrm{Se}$, ${}_{}{}^{80}{}_{}{}^{}\mathrm{Se}$, and ${}_{}{}^{82}{}_{}{}^{}\mathrm{Se}$. All resonances observed in elastic scattering have been fitted using a Coulomb-plus-single-level formula, and $l$ values and resonance parameters have been extracted. The level positions and $l$ values agree quite well with a recent ($d,p$) study of the selenium isotopes, except for one case where two isobaricanalog resonances were reported as a single state in the ($d,p$) work. Coulomb energy differences have been computed for the four pairs of nuclei (${}_{}{}^{77}{}_{}{}^{}\mathrm{Se}$, ${}_{}{}^{77}{}_{}{}^{}\mathrm{Br}$), (${}_{}{}^{79}{}_{}{}^{}\mathrm{Se}$, ${}_{}{}^{79}{}_{}{}^{}\mathrm{Br}$), (${}_{}{}^{81}{}_{}{}^{}\mathrm{Se}$, ${}_{}{}^{81}{}_{}{}^{}\mathrm{Br}$), and (${}_{}{}^{83}{}_{}{}^{}\mathrm{Se}$, ${}_{}{}^{83}{}_{}{}^{}\mathrm{Br}$). Spectroscopic factors have also been calculated for all resonances observed in elastic scattering; these are compared with the spectroscopic factors extracted from the stripping data.