The alpha-particle and lithium-ion recoils from the ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}(n,\alpha )$ reaction were observed in coincidence in face-to-face surface-barrier silicon detectors, using 0.1 atmosphere of ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}_2^{}{}_{}{}^{}$${\mathrm{H}}_6$ as sample. Neutrons were provided by the ORNL 3-MV pulsed Van de Graaff using the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}\mathrm{}(p,n)\mathrm{}$ reaction. Cross-section ratios $\frac{(n,{\alpha }_0)}{(n,{\alpha }_1)}$ of 0.084±0.005 (160 keV), 0.077±0.004 (110 keV), 0.072±0.003 (30 keV), and 0.067±0.002 (thermal neutrons) were found. These results indicate a small monotonic variation in the ratio, in good agreement with earlier measurements at higher energies. Less accurate results are also given at higher energies.

• Received 10 June 1965

DOI:https://doi.org/10.1103/PhysRev.140.B324