THE SPATIAL RESPONSE PATTERN OF GAMMA BACKSCATTER DENSITY GAUGES

This theoretical study shows that the sensitivity of the usual type of gamma backscatter gauge changes markedly for different soil volume elements according to their position with respect to the source and detector locations. There is a maximum in the so-called detector region and a less important maximum in the source region. Calculation shows that 50 per cent of the total response of the instrument originates from 14 per cent by volume of the soil from a hemisphere of diameter d, d being the source-detector separation. Since the response pattern of this type of backscatter gauge is far from uniform, it is necessary to consider the response patterns in planning the conditions of experiments involving these gauges to obtain the highest sensitivity. This is of particular importance in studying soils of a heterogeneous nature.