A total of 236 cross sections for ($n, \mathrm{xn}$) reactions have been measured at neutron energies between 7.5 and 28 MeV, using radiochemical techniques. Cross sections for ($n, n^{\prime }$) and ($n, 2n$) reactions are reported on ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}$; ($n, 2n$) cross sections on ${}_{}{}^{45}{}_{}{}^{}\mathrm{Sc}$ and ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$; ($n, 2n$) and ($n, 3n$) cross sections on ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, and ${}_{}{}^{107}{}_{}{}^{}\mathrm{Ag}$; ($n, 2n$), ($n, 3n$), and ($n, 4n$) cross sections on ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$, ${}_{}{}^{175}{}_{}{}^{}\mathrm{Lu}$, ${}_{}{}^{191}{}_{}{}^{}\mathrm{Ir}$, ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$, and ${}_{}{}^{203}{}_{}{}^{}\mathrm{Tl}$; ($n, 3n$) and ($n, 4n$) cross sections on ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}$; and ($n, 4n$) cross sections on ${}_{}{}^{205}{}_{}{}^{}\mathrm{Tl}$. Neutron fluences were determined by either the ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}(n, \alpha ){}_{}{}^{24}{}_{}{}^{}\mathrm{Na}$ or the ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}(n, 2n){}_{}{}^{89}{}_{}{}^{}\mathrm{Zr}$ reactions appropriately combined with proton-recoil telescope measurements. The excitation functions are compared with calculations based on a model incorporating both compound-nucleus and preequilibrium decay modes. Cross sections for the ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}(n, \alpha ){}_{}{}^{24}{}_{}{}^{}\mathrm{Na}$ reaction between 21 and 26 MeV are also reported.

NUCLEAR REACTIONS ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}(n, \alpha )$, $E=21.4-4-26.0\mathrm{}$ MeV; ${}_{}{}^{45}{}_{}{}^{}\mathrm{Sc}(n, 2n)$, $E=14.1-28.1\mathrm{}$ MeV; ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}(n, 2n)$, $E=16.2-28.1\mathrm{}$ MeV; ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}(n, 2n)$, ($n, 3n$), $E=14.1-28.1\mathrm{}$ MeV; ${}_{}{}^{107}{}_{}{}^{}\mathrm{Ag}(n, 2n)$, ($n, 3n$), $E=13.4-28.1\mathrm{}$ MeV; ${}_{}{}^{151}{}_{}{}^{}\mathrm{Eu}(n, 3n)$, ($n, 4n$) $E=14.8-28.0\mathrm{}$ MeV; ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}(n, 2n)$, ($n, 3n$), ($n, 4n$), $E=8.6-28.0\mathrm{}$ MeV; ${}_{}{}^{191}{}_{}{}^{}\mathrm{Ir}(n, 2n)$, $E=8.6-24.5\mathrm{}$ MeV; ${}_{}{}^{191}{}_{}{}^{}\mathrm{Ir}(n, 3n)$, ($n, 4n$), $E=16.2-28.0\mathrm{}$ MeV; ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}(n, n)$, $E=7.6-14.7\mathrm{}$ MeV; ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}(n, 2n)$, $E=8.6-21.2\mathrm{}$ MeV; ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}(n, 2n)$, ($n, 3n$), ($n, 4n$), $E=8.6-28.1\mathrm{}$ MeV; ${}_{}{}^{203}{}_{}{}^{}\mathrm{Ti}(n, 2n)$, ($n, 3n$), ($n, 4n$), $E=8.6-28.0\mathrm{}$ MeV; ${}_{}{}^{205}{}_{}{}^{}\mathrm{Tl}(n, 4n)$, $E=23.3-28.0\mathrm{}$ MeV; $\mathrm{Zr}(n, xn)$, $E=14.1-28.1\mathrm{}$ MeV; $\mathrm{Lu}(n, xn)$, $E=8.5-28.0\mathrm{}$ MeV; measured $\sigma \mathrm{}\left(E\right)\mathrm{}$. Estimated ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}(n, 2n)$, ($n, 3n$), ${}_{}{}^{175}{}_{}{}^{}\mathrm{Lu}(n, 2n)$, ($n, 3n$), ($n, 4n$), $\sigma \mathrm{}\left(E\right)\mathrm{}$. Comparison with combined statistical and preequilibrium model.

RADIOACTIVITY ${}_{}{}^{189,190}{}_{}{}^{}\mathrm{Ir}$, ${}_{}{}^{193}{}_{}{}^{}\mathrm{Ir}_{}^m{}_{}{}^{}$; measured $T_{\frac{1}{2}}$.

• Received 16 April 1975

DOI:https://doi.org/10.1103/PhysRevC.12.451