Abstract: The present invention provides a method and system which is useful on instruments requiring experimentally determined calibration curves by which calibration data can be transferred to a plurality of field gauges, thereby avoiding the necessity of individually calibrating each gauge each time calibration is necessary. The field gauges are initially cross related to a master gauge. At a later time when a new calibration is necessary, the master gauge is calibrated using carefully prepared samples of a test material. Using the experimentally derived calibration curves with the cross relation data provides calibration data for the field gauges.

Abstract: The nuclear moisture-density gauge of the present invention employs a low activity neutron radiation source and a low activity gamma radiation source. In order to achieve more accurate density measurements at the relatively low count rates which results from the use of a low activity gamma source, the present invention is provided with means for generating a correction signal which is a function of the moisture content of the test material and which represents the amount of gamma radiation emitted from the test material resulting from the neutron capture reaction due to the presence of neutron capture elements, such as hydrogen, present in the test material. This correction signal is applied to the uncorrected density signal obtained from the gauge to thereby obtain a corrected density measurement which is unaffected by background gamma radiation caused by the presence of neutron capture elements in the test material.

Abstract: The present invention provides a nuclear radiation backscatter gauge and method by which an accurate determination of the density of a test material can be made, even though the test material may have surface irregularities or voids which would otherwise contribute significant error to the density measurement. The invention is based upon the use of a nuclear density gauge which is specially designed for measuring thin layers, and which is characterized by having a source and at least two separate detector systems mounted in geometrically differing relationships with respect to the source. Through the use of this type of gauge, in combination with a pad or block of known thickness and density, a measurement is made of the density of a top zone of a predetermined thickness which is greater than the thickness of the block and which thus encompasses not only the block but also an upper portion of the underlying material where the surface voids and irregularities exists.

Abstract: The present invention provides a nuclear radiation backscatter gauge which is capable of directly measuring the density of a thin top layer of material from a composite material comprised of the relatively thin top layer of material applied over an underlying base material. The gauge includes a nuclear radiation source and two radiation detector means so positioned with respect to the source as to form two geometrically differing source-to-detector relationships. A signal processing circuit responds to detected radiation from the two detector means to generate respective signals D.sub.G1 and D.sub.G2 representative of the components densities of the top and base layers as measured by the detector means. The density D.sub.T of the thin top layer is then determined by a signal processing means from the relationship ##EQU1## wherein k.sub.1 and k.sub.2 are empirically derived instrument constants.

Abstract: A method for recalibrating nuclear density gauges comprises the taking of count rate data from two calibration blocks, preferably magnesium and aluminum, for each source depth position of the gauge and thereafter computing new values for constants A and C in a standard working exponential equation for the gauge:CR=A exp (-BD)-C.