Neutron and Photon Emission from Dysprosium and Terbium Compound Nuclei: Range Distributions

Electrostatic collection of Tb and Dy recoils stopped in ${\mathrm{H}}_2$ gas has been explored and found satisfactory for the study of recoil-range distributions. For the reactions ${\mathrm{Pr}}^{141}({\mathrm{C}}^{12}, 4n){\mathrm{Tb}}^{149g}$, ${\mathrm{Nd}}^{146}({\mathrm{B}}^{11}, 8n){\mathrm{Tb}}^{149g}$, ${\mathrm{Nd}}^{144}({\mathrm{C}}^{12}, xn){\mathrm{Dy}}^{156-x}$, and ${\mathrm{Ce}}^{140}({\mathrm{O}}^{16}, xn){\mathrm{Dy}}^{156-x}$ (where $x=5, 6, or 7$), the range distributions are determined by the initial velocity distributions of the recoiling reaction products. The comparison of previously measured angular distributions with these range distributions provides a good method of determining average total neutron energies. The method is relatively insensitive to angular anisotropies $\frac{\left[d\sigma \right(0\mathrm{}°)-d\sigma (90\mathrm{}°\left)\right]}{d\sigma \left(90\mathrm{}°\right)}$ of less than about unity, but can provide clear evidence for strong forward-backward peaking in the angular distribution of the neutrons. The results are consistent with nearly isotropic neutron emission for the latter two reactions, and previously reported neutron energies are supported. Strong forward-backward peaking of the neutrons is indicated for the former two reactions and previously reported neutron energies are corrected by about 20%.