Interaction of Fast Neutrons with OrientedHo165

Abstract

Total cross-section and angular distribution measurements are reported for 8- and 15-MeV neutrons incident on unoriented ${\mathrm{Ho}}^{165}$. Measurements of the "deformation effect" in the total cross section for unpolarized neutrons incident on oriented ${\mathrm{Ho}}^{165}$ at 8 and 15 MeV are also reported. The first and second moments of the nuclear orientation were $\frac{B_1}{B_1\left(max\right)}=+0.55\mathrm{}$ and $\frac{B_2}{B_2\left(max\right)}=+0.25\mathrm{}$. If the "deformation effect" is defined by $\Delta {\sigma }_{\mathrm{Def}}=\sigma \left(\mathrm{oriented}\right)-\sigma \left(\mathrm{unoriented}\right)$, the experimental results for $\Delta {\sigma }_{\mathrm{Def}}$ are -38±10 mb and -139±16 mb at 8 and 15 MeV, respectively. The above data are explained by a coupled-channel analysis based on the rotational optical model, and the optical parameters derived from this analysis are used to interpret a measurement of the "spin-spin effect" at $E_n=7.85\mathrm{}$ MeV. The neutron polarization for the measurement was 0.34. If the "spin-spin effect" is defined by $\Delta {\sigma }_{\mathrm{ss}}={\sigma }_{\uparrow \uparrow }-{\sigma }_{\uparrow \downarrow }$, the experimental result for $\Delta {\sigma }_{\mathrm{ss}}$ is +3±13 mb at $E_n=7.85\mathrm{}$ MeV. If $\Delta {\sigma }_{\mathrm{ss}}$ is assumed to arise from a term of the form $-V_{\mathrm{ss}}f(r, r_0{A}^{\frac{1}{3}}, a)\times \mathrm{I}·\frac{\sigma }{I}$ in the optical potential, the acceptable limits on the strength of the potential are $-340\mathrm{} \mathrm{keV}<V_{\mathrm{ss}}<540\mathrm{} \mathrm{keV}$. The present experimental results are compared with other published data on the interaction of neutrons with oriented ${\mathrm{Ho}}^{165}$.