The (α, n) and (α, 2n) Cross Sections ofAg109

The excitation curves for the reactions ${\mathrm{Ag}}^{109}(\alpha , n){\mathrm{In}}^{112}$ and ${\mathrm{Ag}}^{109}(\alpha , 2n){\mathrm{In}}^{111}$ have been measured for alpha-energies up to 19.5 Mev. The threshold for the ($\alpha , 2n$) reaction is 14.8±0.2 Mev. The sum of the cross sections agrees approximately with the total cross section calculated for a radius $R\sim 1.6\times {10}^{-13\mathrm{}}{A}^{\frac{1}{3}}$ cm. The energy dependence of the ratio $\frac{\sigma (\alpha , 2n)}{\sigma (\alpha , n)}$ can be interpreted as being in agreement with either a nearly constant nuclear temperature of 1.7 Mev or with a level density $\omega \mathrm{}\left(E\right)=\mathrm{const}\exp \left[2\mathrm{}{\mathrm{}\left(\mathrm{aE}\right)\mathrm{}}^{\frac{1}{2}}\right]$ with $a=2.5\mathrm{}$ ${\mathrm{Mev}}^{-1\mathrm{}}$. The corresponding temperature $\ominus ={\left(\frac{E}{a}\right)}^{\frac{1}{2}}$ varies from 1.7 Mev to 2.2 Mev for excitation energies between 7.5 and 12 Mev. These apparent temperatures are considerably higher than those found by direct measurement of ($p, n$) and ($n, n$) neutron spectra.