One-block calibration method for density gauges

A method of calibrating a nuclear density gauge of the type having a gamma source which is positionable at several different source depth positions with respect to a detector to obtain the calibration constants A, B and C of the exponential equation

• CR=A exp(-BD)+C
• where:
• CR is the count ratio dervied by comparing an accumulated count from a test specimen to a standard count,
• D is the density of the test specimen, and
• A, B and C are calibration constants,
• said method being characterized by reducing the number of experimental count readings required for calibration, and said method comprising the steps of:
• (a) positioning the source at a predetermined source depth position on or in a calibration block of known density and obtaining a count by the detector for a predetermined period of time;
• (b) calculating at least one additional count at another known density or another known source depth position using historically derived relationships between the count obtained from said calibration block of known density and the counts obtained from calibration blocks of other known densities and other known source depth positions;
• and
• (c) utilizing the experimental count obtained from step (a) and the calculated count obtained from step (b), together with the respective densities, to derive a set of calibration constants A, B and C.