Monte-Carlo calculations for the subsurface gamma density gauge

Some characteristics of the subsurface gamma density gauge are investigated by means of a Monte Carlo model. The model, which is one-dimensional and spherical, accounts for the effect of the shielding between source and detector in a simplified manner.The influence of Z_eq, and a finite volume of the measured medium on the gauge response is studied attentively. For densities above 1 g/cm³, the radius of the sphere of importance is about 26–40 cm and considerably large at lower densities.Attention is further paid to the dual-gauge concept with two different source-detector distances. Important advantages of this concept are diminished influence of Z_eq and somewhat increased density measuring range, whereas longer counting times and a more complicated gauge configuration seem to be the main drawbacks.Good agreement between the calculations and measurements with the BASC gauge is obtained, if maximally two experimentally determined parameters are introduced.