Experimental (n,${\hat{I}}^3$) cross sections of the p-process nuclei ${}^{74}$Se and ${}^{84}$Sr

Abstract

The nucleosynthesis of elements beyond iron is dominated by the s and r processes. However, a small amount of stable isotopes on the proton-rich side cannot be made by neutron capture and are thought to be produced by photodisintegration reactions on existing seed nuclei in the so-called "p process". So far most of the p-process reactions are not yet accessible by experimental techniques and have to be inferred from statistical Hauser-Feshbach model calculations. The parametrization of these models has to be constrained by measurements on stable proton-rich nuclei. A series of (n,${\hat{I}}^3$) activation measurements, related by detailed balance to the respective photodisintegrations, were carried out at the Karlsruhe Van de Graaff accelerator using the ${}^7$Li(p,n)${}^7$Be source for simulating a Maxwellian neutron distribution of kT= 25 keV. First results for the experimental (n,${\hat{I}}^3$) cross sections of the light p nuclei ${}^{74}$Se and ${}^{84}$Sr are reported. These experimental values were used for an extrapolation to the Maxwellian averaged cross section at 30 keV, $<\ddot{I}ƒ{>}_{30}$, yielding 271$\pm$15 mb for ${}^{74}$Se, and 300$\pm$17 mb for the total capture cross section of ${}^{84}$Sr. The partial cross section to the isomer in ${}^{85}$Sr was found to be 190$\pm$10 mb.

10 pages, 5 figures