Differential Cross Sections of theK39,41(n, n′γ)Reactions

Differential production cross sections of the ${}_{}{}^{39,41}{}_{}{}^{}\mathrm{K}(n, n^{\prime }\gamma )$ and ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}(n, p\gamma )$ reactions have been measured at incident neutron energies of 1.82, 2.63, 3.42, and 3.96 MeV. $\gamma$ rays were detected with NaI(Tl) and Ge(Li) detectors using pulsed-beam techniques to eliminate backgrounds. Transition-energy measurements of the Ge(Li) detector fix the first excited state of ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ at 2.519±0.003 MeV. Interpretation of the $\gamma$-ray angular distributions and production cross sections permitted spin assignments to ${}_{}{}^{39,41}{}_{}{}^{}\mathrm{K}$ levels. The ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}$ levels assigned (excitation in MeV, spin) are 2.817, $\frac{7}{2}$; 3.021, $\frac{3}{2}$; 3.603, $\frac{9}{2}$. Those assigned in ${}_{}{}^{41}{}_{}{}^{}\mathrm{K}$ are 0.978, ½ or $\frac{3}{2}$; 1.291, $\frac{7}{2}$; 1.58, $\frac{9}{2}$ or $\frac{11}{2}$.