Numerical simulation of pulsed neutron source density logging's secondary captured gamma ray strength

To reduce the radiological hazards of isotopic neutron source used in conventional density logging instrument, controlled pulsed neutron source is widely used instead of conventional chemical source. A fast neutron emitted from the pulsed neutron source is captured by atomic nucleus after decelerating and diffusing of stratum, and releases captured gamma ray. We use Monte Carlo method to simulate the process of fast neutron departed from source and getting through stratum to get the intensity distribution of captured gamma ray, regard the captured gamma ray as the gamma source of density logging, simulate the relations between stratum density and the intensity distribution of remaining gamma ray after stratum absorption and study on the influence measurement conditions to the remaining gamma ray intensity. The results show that as the stratum density increases, the remaining gamma ray intensity decreases. The fitting relationship between the remaining gamma ray intensity and stratum density is built, which can guide to design pulsed neutron source density logging instrument.