Elastic and Inelastic Scattering of Protons from Krypton

Abstract

Elastic and inelastic scattering of protons from krypton has been investigated for the bombarding energy range 3.6-5.4 MeV. Resonances were observed in the elastic scattering and in the inelastic scattering to the first ${2}^{+}$ (0.877\ifmmode\pm\else\textpm\fi{}0.011 MeV) state in $^{84}\mathrm{Kr}$. The resonant energies are (as obtained from the inelastic scattering yield curves) 4.990\ifmmode\pm\else\textpm\fi{}0.017 and 5.277\ifmmode\pm\else\textpm\fi{}0.017 MeV. Resonance parameters obtained by the use of the optical model with an added isolated resonance term suggest that these resonances are due to isobaric analog states of hitherto unreported low-lying states of $^{85}\mathrm{Kr}$ with 1.23-MeV (${J}^{\ensuremath{\pi}}={\frac{3}{2}}^{+} or {\frac{5}{2}}^{+}$) and 1.52-MeV (${J}^{\ensuremath{\pi}}={\frac{1}{2}}^{+}$) excitation energies. These excitation energies have an associated maximum uncertainty of \ifmmode\pm\else\textpm\fi{}100 keV. Angular distributions of the inelastic protons from the $^{84}\mathrm{Kr}(p, {p}^{\ensuremath{'}})^{84}\mathrm{Kr}$ (0.877 MeV) measured on these resonance peaks show interference effects. Isobaric analogs of those states strongly excited via the $^{86}\mathrm{Kr}(d, t)^{85}\mathrm{Kr}$ neutron pickup reaction were not observed in the present investigation, thus confirming their "neutron-hole" nature. Inelastic scattering to the first ${2}^{+}$ (0.771\ifmmode\pm\else\textpm\fi{}0.011 MeV) and the second ${2}^{+}$ (1.470\ifmmode\pm\else\textpm\fi{}0.007 MeV) states of $^{82}\mathrm{Kr}$ was studied for the bombarding energy range 4.9-5.4 MeV. The yield of protons going to the first excited state resonates at 5.34 MeV. If one assumes that this resonance is a manifestation of an analog of a low-lying state of $^{83}\mathrm{Kr}$, the excitation energy is 1.89 MeV, again with a maximum uncertainty of about \ifmmode\pm\else\textpm\fi{}100 keV. No resonance is seen for the yield to the 1470-keV second excited state. The effect of the compound-nuclear-reaction mechanism on the inelastic cross sections has been investigated. Theoretical off-resonance inelastic cross sections calculated by the Hauser-Feshbach formalism of statistical compound-nuclear reactions agree with the experimental results quite satisfactorily.