One-block calibration method for density gauges

Nuclear density gauges of the type having a gamma source which is positionable at several different source depth positions with respect to a detector are calibrated in an efficient and advantageous manner by a calibration procedure which reduces the number of experimental counts which must be taken. In accordance with the present invention, a single calibration block is employed and counts are taken at one or more source depth positions on the block. Through the use of historically derived relationships between the count rate obtained from the calibration block to the count rates obtained from at least two different calibration blocks of other known densities, the expected calibration counting rates for the other blocks can be obtained. These calculated counting rates are then used along with the experimentally determined counting rate to obtain the calibration constants for the gauge.