(α, n) Reactions in Some Elements in the Region ofA=100

Absolute ($\alpha , n$) cross sections and angular distributions from 0 to 160° have been measured for Y, Nb, Rh, Ag, ${\mathrm{Ag}}^{109}$, and In, from 12 to 18 MeV. The angular distributions show almost complete isotropy, with a systematic trend toward a forward peaking never larger than 5 to 10%. Since, in these elements, neutron emission is expected to be the main contribution to the reaction cross section, the measured ($\alpha , n$) cross sections have been compared with the predictions of the optical model. Different optical-model potentials for $\alpha$ particles have been tried. Very good agreement with the experimental results has been obtained with the "Igo potential." Reaction cross sections for a square-well potential following Shapiro's calculation for a radius ($1.7A^{\frac{1}{3}}+1.21\mathrm{}$) $F$ appear to be in the right order of magnitude, but they do not reproduce the dependence of the excitation function on the incident $\alpha$ energy.