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

摘要

When a thermal neutron is absorbed by ~(10)B in the ~(10)B(n,α)~7Li reaction, there is a chance of 94% that a 478 keV photon be emitted by an excited ~7Li nucleus. This reaction is exothermic with a Q-value of 2.31 MeV and the nuclei are emitted with kinetic energies of E(α)=1.47 MeV and E(~7Li~*)=0.84 MeV. This implies that the 478 keV γ line is emitted by a moving ~7Li nucleus and hence is expected to be Doppler broadened. In the present work we suggest to use this broadening of the γ 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 (B_4C) sheet to calculate the γ line broadening. Our simulation shows that the FWHM width of the resulting γ line is 12.6 keV, in good agreement with our measurement. Hence the broadened γ line emitted by the ~(10)B(n,αγ)~7Li reaction and detected by a HPGe detector shows that this method is an effective tool for neutron detection while maintaining good gamma discrimination.