Bromine and iodine excitation-function measurements with protons and deuterons at 3–17 MeV

Abstract

We report nuclear excitation functions for the reactions $^{79}[$(p,n)+(d,2n)${]}^{79}$Kr, $^{81}[$(p,n)+ (d,2n)${]}^{81}$Br, $^{81}\mathrm{Br}$(d,p${)}^{82}$Br, and $^{127}[$(p,n)+(d,2n)${]}^{127}$Xe. The measurements were made from reaction threshold to 17 MeV with the Lawrence Livermore National Laboratory's Tandem Van de Graaff accelerator using the stacked-foil method. The $^{79}\mathrm{Br}$(d,2n${)}^{79}$Kr and the $^{81}\mathrm{Br}$ excitation functions are the first reported. The targets consisted of the halides dispersed in the plastic Kapton. The activated targets were assayed using \ensuremath{\gamma} counting and mass spectrometry. We found that we had to remeasure the gamma intensities for the $^{79}\mathrm{Kr}$ decay. The excitation functions were modeled using the Hauser-Feshbach statistical-model code stapre, using the exciton preequilibrium model. We found a preference for the back-shifted (BS) level density prescription over the use of the Gilbert-Cameron prescription. For BS, the constant K, governing the transition to equilibrium, was taken as 500 to 700 ${\mathrm{MeV}}^{3}$. These values gave preequilibrium fractions consistent with those we obtained from ion-recoil range studies of light ion reactions. In general the modeling agreed well with experiment. For the deuteron induced reactions, we had to allow for deuteron breakup using a microscopic breakup fusion approach developed by Udagawa and Tamura. Our analysis of the stripping reaction, $^{81}\mathrm{Br}$(d,p${)}^{82}$Br, by this procedure is especially noteworthy.