Possibilities of eliminating composition errors in gamma ray backscatter density measurement

Abstract

The method of determining soil and building material densities by gamma ray backscatter gauges has been developed successfully in recent years. However, with regard to the accuracy of measurement, this method is subject to various sources of interference which are being eliminated more or less successfully in the course of its practical application. One of the major factors affecting accuracy unfavourably is the variation in chemical composition of samples tested. In this paper the possibility of eliminating errors due to variation in chemical composition by using the air-gap technique or the dual-gauge principle is discussed. Results of experimental measurements using these two methods are compared with results achieved by the single-gauge technique using one detector seated close to the surface of the sample tested. The values obtained are analyzed by a Hewlett-Packard 9820 computer program. The results of various measurements are given and compared. All measurements were accomplished by means of an NaJ(T1) scintillation detector and for 137Cs and 60Co sources.