Excitation functions of (n,t) reactions onAl27,Co59, andNb93

Cross sections were measured for ($n$,$t$) reactions on ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$, and ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ over the incident neutron energy region of 16 to 20 MeV using activation and tritium counting. Three or four segments of the material under investigation were so arranged that a compact hemispherical geometry was obtained. The incident neutrons were produced by the ${}_{}{}^3{}_{}{}^{}\mathrm{H}$($d$,$n$)${}_{}{}^4{}_{}{}^{}\mathrm{He}$ reaction and the neutron energy spectrum effective for each segment was determined via Monte Carlo calculations. After irradiation, the accumulated tritium was separated from each segment by vacuum extraction and its activity determined by lowlevel anticoincidence ${\beta }^{-}$ counting in the gas phase. The ($n$,$t$) cross section increases with the incident neutron energy. The excitation function of the ($n$,$t$) reaction on ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ is described well by Hauser-Feshbach calculations; in the case of ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$ and ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$, however, the calculated cross section values are appreciably smaller than the experimental data, suggesting that for those nuclei the contributions of statistical processes are rather small.