Using the Doppler broadened γ line of the 10B(n,αγ)7Li reaction for thermal neutron detection

When a thermal neutron is absorbed by B-10 in the B-10(n,alpha)Li-7 reaction, there is a chance of 94% that a 478 keV photon be emitted by an excited Li-7 nucleus. This reaction is exothermic with a Q-value of 2.31 MeV and the nuclei are emitted with kinetic energies of E(alpha)=1.47 MeV and E(Li-7*)=0.84 MeV. This implies that the 478 keV gamma line is emitted by a moving Li-7 nucleus and hence is expected to be Doppler broadened. In the present work we suggest to use this broadening of the gamma line as a fingerprint for the detection of thermal neutrons using a high resolution gamma spectrometer. We thus developed a Monte Carlo program using a MATLAB code based on a High Purity Germanium (HPGe) detector coupled with a Boron Carbide (B4C) sheet to calculate the gamma line broadening. Our simulation shows that the FWHM width of the resulting gamma line is 12.6 keV, in good agreement with our measurement. Hence the broadened gamma line emitted by the B-10(n,alpha y)Li-7 reaction and detected by a HPGe detector shows that this method is an effective tool for neutron detection while maintaining good gamma discrimination. (C) 2015 Elsevier B.V. All rights reserved.