MEASUREMENT OF 10B(N,ALPHA)7LI,7LI] RELATIVE CROSS SECTIONS IN KEV REGION

Relative cross sections for 10B(n, α)7Li, 7Li* were obtained from measurements of the counting ratios of a 10BF3 proportional counter and a precision long counter used to monitor relative neutron fluxes. Mono-energetic neutrons were produced by a Van de Graaff accelerator in the energy region from 30 to 800 keV. When the relative cross sections are normalized to a 1/v variation below 80 keV, the data lie above a 1/v line from 80 to 550 keV indicating departures of 15% at 140 keV and 20% at 220 keV. Measurements were also made of the relative efficiency of a modified long counter used by Bichsel and Bonner to monitor neutron flux in their measurements of the 10B(n, α)7Li, 7Li* cross sections. The Bichsel and Bonner cross sections also lie above a 1/v line from 80 to 200 keV when corrected for the efficiency of their flux monitor. Recommended cross sections for 10B(n, α)7Li 7Li* up to 1 MeV are obtained from recently available measurements and the known levels in 11B. © 1969.