Modelling gamma-source backscatter density gauges

Gamma-source backscatter gauges are used to obtain a nonintrusive measurement of the density of rocks and soils from the surface. The static and moving-source versions of these instruments, which have been developed previously, allow an in situ investigation of a bulk sample of a material. Changes in gauge design and factors affecting the homogeneity of the material alter the backscatter characteristics. A model, which accurately represents the detector in its working environment, is developed for all gamma-source backscatter density gauges. Whereas previous models emulate the absorption and scattering processes, the presented model allows a direct comparison of the maxima and shape, or bandwidth, of the experimental and theoretically predicted results. The model makes this comparison possible through the formulation of characteristic differential equations together with accurate calculations of both the maxima and normalised bandwidth of the characteristics, for both versions of these back-scatter density gauges. This allows an accurate comparison of design parameters by different routes and could form a basis for new backscatter gauge designs. Fresh applications involving surface measurements of in situ bulk materials could also result from this model.