(n, γ) Cross Sections ofNa23,I127, andAu197

The cross sections for the ${\mathrm{Na}}^{23}(n, \gamma ){\mathrm{Na}}^{24}$ and the ${\mathrm{I}}^{127}(n, \gamma ){\mathrm{I}}^{128}$ reactions have been measured by an activation method over the neutron energy range 20 kev to 1 Mev. The neutron flux was measured with a fission detector which contained a thin layer of known weight of ${\mathrm{U}}^{235}$. The ${\mathrm{Na}}^{23}$ cross-section variation with energy shows incompletely resolved resonance structure; an average curve through the data decreases as $\frac{1}{v_n}$ from 2.4 mb at 20 kev to 0.6 mb at 300 kev, and as $\frac{1}{E_n}$ from 0.6 mb at 300 kev to 0.2 mb at 1 Mev. The ${\mathrm{I}}^{127}$ cross section can be represented approximately by a straight line on a log-log plot, decreasing from 1.0 barn at 30 kev to 80 mb at 1 Mev. The ${\mathrm{Au}}^{197}(n, \gamma ){\mathrm{Au}}^{198}$ cross section, measured at a neutron energy of 180 kev, is 310±20 mb.