($n,2n$) Reactions in ${\mathrm{C}}^{12}$, ${\mathrm{Cu}}^{63}$, and ${\mathrm{Mo}}^{92}$

Using the method of induced radioactivity we have measured the ($n,2n$) cross sections of ${\mathrm{C}}^{12}$, ${\mathrm{Cu}}^{63}$, and ${\mathrm{Mo}}^{92}$ as a function of energy from threshold to 27 Mev. The positron activities of 20, 10, and 15.5 min, respectively, were employed. K-capture corrections were applied to the copper and molybdenum data. We have compared the copper and molybdenum data with the statistical theory of Weisskopf and collaborators and find satisfactory agreement from threshold to the onset of tertiary reactions.