CALIBRATION, STABILITY AND USE OF NUCLEAR METERS

Determination of density and moisture content by nuclear meters is an indirect method of measurement and calibration equations are necessary to relate instrument response to the magnitude of the property being measured. Initially the meters were calibrated against the results of sand replacement tests or against the average densities and moisture contents of materials compacted in boxes of known volume. The shortcomings of these methods were the uncertainty whether the densities and moisture contents quoted are applicable to the calibration, the lack of repeatability and reproducibility, and the length of time and the number of personnel required. Calibration on standard blocks overcomes these problems and is recommended. The density standard blocks are cut from rocks selected for uniformity, the moisture standard blocks are made from sand polystyrene blends. In addition to the stability checks recommended by the manufacturers, consistency checks should be carried out at regular intervals. Thorough training of the operators and adherence to detailed test methods is essential. Density measurements should be carried out in the direct transmission mode. This paper was presented at Session II: Field Measurement of Density. For the covering abstract of the conference, see TRIS no. 378031. (Author/TRRL)