Production cross sections of ground and isomeric states in the reaction systems93Nb+3He,92Mo+α,and94,95Mo+p

Abstract

Cross-section measurements on the production of ${}^{94}{\mathrm{Tc}}^{m}$ in the reactions ${}^{93}\mathrm{Nb}{(}^{3}\mathrm{He},2n),$ ${}^{92}\mathrm{Mo}(\ensuremath{\alpha},x),$ and ${}^{94}\mathrm{Mo}(p,n)$ were performed recently at J\"ulich in order to investigate ways of producing this radioisotope on a large scale for nuclear medical application. Those experiments also yielded the excitation functions for the reactions ${}^{93}\mathrm{Nb}{(}^{3}\mathrm{He}{,xn)}^{95,94,93}{\mathrm{Tc}}^{m,g}$ $(x=1,2,3),$ ${}^{93}\mathrm{Nb}{(}^{3}\mathrm{He}{,x)}^{93}{\mathrm{Mo}}^{m},$ ${}^{93}\mathrm{Nb}{(}^{3}\mathrm{He}{,x)}^{92}{\mathrm{Nb}}^{m}$ and ${}^{93}\mathrm{Nb}{(}^{3}\mathrm{He}{,x)}^{89}{\mathrm{Zr}}^{m+g},$ ${}^{92}\mathrm{Mo}(\ensuremath{\alpha}{,xn)}^{95,94}\mathrm{Ru}$ $(x=1,2),$ ${}^{92}\mathrm{Mo}(\ensuremath{\alpha}{,x)}^{94}{\mathrm{Tc}}^{m,g}$, and ${}^{92}\mathrm{Mo}(\ensuremath{\alpha}{,p)}^{95}{\mathrm{Tc}}^{g}$ as well as ${}^{94}\mathrm{Mo}{(p,xn)}^{94,93}{\mathrm{Tc}}^{m,g}$ $(x=1,2).$ A theoretical study, employing the Hauser-Feshbach and the exciton-model formalism, was now undertaken to describe the cross sections of all those reactions. The data base was supplemented by cross sections retrieved from the literature, including the reactions ${}^{93}\mathrm{Nb}{(}^{3}\mathrm{He}{,4n)}^{92}\mathrm{Tc},$ ${}^{92}\mathrm{Mo}(\ensuremath{\alpha}{,p)}^{95}{\mathrm{Tc}}^{m},$ ${}^{92}\mathrm{Mo}(\ensuremath{\alpha}{,x)}^{93}{\mathrm{Tc}}^{m,g},$ and ${}^{95}\mathrm{Mo}{(p,n)}^{95}{\mathrm{Tc}}^{m,g}.$ As the reactions investigated have many of the product nuclei in common, they permit the study of cross sections, in particular for the formation of pairs of isomeric states, as functions of projectile type and energy, with the cross sections for formation of nuclei via competing reactions posing additional constraints on the model parameters. Considering the rather large scatter among the experimental data sets, as well as the fact that attempts were made to describe simultaneously 25 excitation functions and 8 isomeric cross-section ratios $[{\ensuremath{\sigma}}^{m}/({\ensuremath{\sigma}}^{m}+{\ensuremath{\sigma}}^{g})]$ with one consistent set of model parameters, the degree of agreement achieved between experimental and calculated quantities is remarkable. In ${}^{3}\mathrm{He}$-induced reactions, the adoption of a spin distribution of the level population in preequilibrium emission different from that at the equilibrium stage yielded some improvement in the description of the isomeric ratios for ${}^{95,94,93}\mathrm{Tc}$ production.