Cross Section for the ${\mathrm{Li}}^6(n, \alpha ){\mathrm{H}}^3$ Reaction for $1.2<~E_n<~8.0$ Mev

The cross section for the reaction ${\mathrm{Li}}^6(n, \alpha ){\mathrm{H}}^3$ has been measured as a function of neutron energy in the range $1.2<~E_n<~8.0$ Mev. An essentially back-to-back method was used, with a thin cylindrical ${\mathrm{Li}}^6$I(Eu) scintillation crystal placed concentric with and adjacent to a thin-walled ionization chamber containing a deposit of fissile material (${\mathrm{U}}^{238}$ or ${\mathrm{Np}}^{237}$). The magnitude of ${\sigma }_{n,\alpha }$ as measured in this experiment depends on the absolute value of ${\sigma }_{\mathrm{fiss}}\left({\mathrm{U}}^{238}\right)$, while the shape of the cross section vs energy curve depends on the known energy dependence of ${\sigma }_{\mathrm{fiss}}({\mathrm{U}}^{238} or {\mathrm{Np}}^{237})$. Statistical and other point-to-point uncertainties in the data range from ±5 to ±9%, while the uncertainty in absolute value of the cross section is ±7%. The cross section obtained from these measurements decreases monotonically from a value of 0.28 barn at $E_n=1.2\mathrm{} \mathrm{Mev}\mathrm{to} 0.051 \mathrm{barn}$ barn at $E_n=8.0\mathrm{}$ Mev.