Differential cross sections for the 10B(n,α)7Li, 7Li* reactions

The usefulness of the 10B(n, α)7Li, 7Li* reactions for neutron detectors and flux standards justifies efforts to obtain a more accurate knowledge of integrated and differential cross sections. Measurements of α-particle yields from these reactions have been made at 8 angles from 00 to 1500 for neutron energies from 200 to 1250 keV. The neutron source was a thick natural lithium target bombarded by a 3.0 MeV pulsed proton beam. An evacuated, low-mass target chamber housed the 10B target and a silicon surface barrier detector. The detector was used to measure α-particle energies and to provide a timing signal. This timing signal and another derived from a ferrite core beam pulse pickoff were used to measure the total flight time of the neutrons and resultant α particles. When counts were stored in a two-dimensional array of total flight time versus energy, ground state and first excited state α particles were separated from background as well as from each other. Yields were converted to differential cross sections at calculated mean reaction angles and neutron energies. Angular distributions were least fitted to a sum of Legendre polynomials for 22 neutron energies. The coefficients of the P0 terms have been used to calculate integrated cross sections, absorption cross sections, and branching ratios. These agree, within errors, with other measurements except for a broad peak at 350 keV in the ground state cross sections not seen by others. The coefficients of the P1 terms for both reactions indicate interference between a p-wave state at E/sub n/ = 530 keV and nearby s-wave states. A four term fit was required for the first excited state reaction for E/sub n/ = 300 to 500 keV, suggesting the presence of a d-wave state