Moisture effect in prompt gamma measurements from soil samples

The variation in intensity of 1.78 MeV silicon, 6.13 MeV oxygen, and 2.22 MeV hydrogen prompt gamma rays from soil samples due to the addition of 5.1, 7.4, 9.7, 11.9 and 14.0 wt% water was studied for 14 MeV incident neutron beams utilizing a LaBr₃:Ce gamma ray detector. The intensities of 1.78 MeV and 6.13 MeV gamma rays from silicon and oxygen, respectively, decreased with increasing sample moisture. The intensity of 2.22 MeV hydrogen gamma rays increases with moisture. The decrease in intensity of silicon and oxygen gamma rays with moisture concentration indicates a loss of 14 MeV neutron flux, while the increase in intensity of 2.22 MeV gamma rays with moisture indicates an increase in thermal neutron flux due to increasing concentration of moisture. The experimental intensities of silicon, oxygen and hydrogen prompt gamma rays, measured as a function of moisture concentration in the soil samples, are in good agreement with the theoretical results obtained through Monte Carlo calculations.