Excitation functions have been measured for the ($\alpha , n$), ($\alpha , 2n$), and ($\alpha , \alpha n$) reactions on ${\mathrm{Cu}}^{63}$ and ${\mathrm{Cu}}^{65}$, as well as for the ${\mathrm{Cu}}^{63}(\alpha , pn)$, ${\mathrm{Cu}}^{65}(\alpha , 2p)$, and ${\mathrm{Cu}}^{65}(\alpha , 2\alpha )$ reactions, for incident alpha particles of 15-41 Mev. The excitation functions for the ($\alpha , n$), ($\alpha , 2n$), and ($\alpha , \mathrm{pn}$) reactions go through much sharper maxima than the excitation functions for the ($\alpha , \alpha n$) reactions. Cross sections for the ($\alpha , 2p$) and ($\alpha , 2\alpha$) reactions increase monotomically with bombarding energy and attain values of 2.7 and 2.1 mb at 40 Mev, respectively. The value of $\frac{\sigma (\alpha , pn)}{\sigma (\alpha , 2n)}$ for ${\mathrm{Cu}}^{63}$ in the region of maximum yield is 3.3. The maximum cross sections measured for the ($\alpha , \alpha n$) reactions are 205 mb and 143 mb for ${\mathrm{Cu}}^{63}$ and ${\mathrm{Cu}}^{65}$, respectively. The effects on the observed cross sections of neutron and proton binding energy differences, and of level density differences in the residual nuclei have been considered. The effect of these factors is in accord with the predictions of the statistical theory for the ($\alpha , n$) and ($\alpha , 2n$) reactions but not for the ($\alpha , \alpha n$) reaction.

A method for monitoring the energy of the incident beam based on the variation with energy of the ratio of cross sections for several of the above reactions is described.

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