Interpretation of Experimental (n, 2n) Excitation Functions

Radiochemically determined ($n, 2n$) excitation functions for ${\mathrm{Sc}}^{45}$, ${\mathrm{Ti}}^{46}$, ${\mathrm{Ni}}^{58}$, ${\mathrm{Cu}}^{65}$, ${\mathrm{Ge}}^{70}$, ${\mathrm{As}}^{75}$, ${\mathrm{Sr}}^{84}$, ${\mathrm{Rb}}^{85}$, ${\mathrm{Rb}}^{87}$, ${\mathrm{Y}}^{89}$, ${\mathrm{Zr}}^{90}$, ${\mathrm{Sn}}^{112}$, ${\mathrm{Cd}}^{116}$, ${\mathrm{Sb}}^{123}$, and ${\mathrm{U}}^{238}$ have been interpreted in terms of the statistical model of nuclear reactions. Values of the level density parameter $a$ are obtained and correlated with mass number. A procedure is outlined for predicting the magnitude of any ($n, 2n$) cross section from the nuclear content of the target material. Two level density formulations are studied, and approximations customarily made in calculations of this sort are examined quantitatively.