A high-energy gamma-ray source based on neutron capture

Abstract

In special applications, high-energy gamma rays are needed to calibrate the energy response of a detector. However, the energies of commonly used radioactive gamma-ray sources are lower than 3 MeV. An alternative source is the prompt gamma rays created by the radiative capture of thermal neutrons. In this study, a 5×104 neutrons/s Am–Be neutron source was used to emit fast neutrons that were moderated in paraffin and then absorbed by Ni (nickel), which captured thermal neutrons and generated monochromatic high-energy gamma rays in the range 5–9 MeV. The 8.99 MeV line in this was the strongest. The paraffin and Ni were mixed uniformly to increase the yield of the high-energy gamma rays, and the optimal mass ratio of paraffin to Ni was calculated by GEANT4. According to the results of simulations, a 200×200×200 mm3 neutron-capturing device was built with a mass ratio of paraffin to Ni of 3:7. Finally, spectra of the high-energy gamma rays emitted by the device were measured by a 38.1 mm (diameter) × 38.1 mm (thickness) LaBr3:Ce detector, and most characteristic energy peaks were clearly visible.