ReactionB11(n, α)Li8(β−)Be8*(2α)for 12- to 20-Mev Neutrons

Ilford 200-μ C-2 plates loaded with ${\mathrm{B}}^{11}$ were exposed to monoenergetic neutrons produced at nine angles to a 3.5-Mev deuteron beam incident upon a tritium gas target. Mesurements of range and space angles were made upon 450 "hammer stars" which were found to result from the ${\mathrm{B}}^{11}(n, \alpha ){\mathrm{Li}}^8\left({\beta }^{-}\right){\mathrm{Be}}^{8*}\left(2\mathrm{}\alpha \right)$ reaction. The cross sections in mb as a function of energy in Mev are as follows: 12.6 Mev, 27.0±6.5 mb; 13.0, 38.4±7.4; 14.7, 30.9±6.3; 15.4, 36.9±7.0; 16.9, 21.9±3.6; 17.6, 23.7±4.8; 18.9, 19.7±3.7; 19.8, 16.3±3.1; 20.0, 15.8±3.1. The angular distribution of the alpha particles from the ($n, \alpha$) reaction is obtained at each energy. In nearly all cases the ${\mathrm{Li}}^8$ is left in the ground state or in the first excited state of 1 Mev. The ${\mathrm{Be}}^8$ disintegration goes through the broad 3-Mev level and possibly a lower level near 2 Mev. A range-energy relation is found for ${\mathrm{Li}}^8$ in Ilford C-2 emulsion. Comparison with previous experimental results shows closest agreement with Barkas.