This test method describes the procedure for determining the in-place density and moisture of soil and soil-aggregate by use of nuclear gauge. The density of the material may be determined by either direct transmission@ backscatter@ or backscatter/air?Cgap ratio method. The moisture of the material is determined only from measurements taken at the surface of the soil (i.e.@ backscatter). Density??The total or wet density of soil and soil?Crock mixtures is determined by the attenuation of gamma radiation where the source or detector is placed at a known depth up to 300 mm (12 in.) while the detector(s) or source remains on the surface (Direct Transmission Method) or the source and detector(s) remain on the surface (Backscatter Method). The density in mass per unit volume of the material under test is determined by comparing the detected rate of gamma radiation with previously established calibration data. Moisture??The moisture content of the soil and soil-rock mixtures is determined by thermalization or slowing of fast neutrons where the neutron source and the thermal neutron detector both remain at the surface. The water content in mass per unit volume of the material under test is determined by comparing the detection rate of thermalized or slow neutrons with previously established calibration data. SI Units??The values stated in SI units are to be regarded as the standard. The inch?Cpound equivalents may be approximate. It is common practice in the engineering profession to concurrently use pounds to represent both a unit of mass (lbm) and of force (lbf). This implicitly combines two systems of units@ that is@ the absolute system and the gravitational system. This standard has been written using the absolute system for water content (kilograms per cubic meter) in SI units. Conversion to the gravitational system of unit weight in lbf/ft3 may be made. The recording of water content in pound-force per cubic foot should not be regarded as nonconformance with this standard although the use is scientifically incorrect. In the English system@ the pound (lbf) represents a unit of force (weight). However@ the use of balances or scales recording pounds of mass (lbm)@ or recording of density (lbm/ft3) should not be regarded as nonconformance with this standard. This standard does not purport to address all of the safety problems@ if any@ associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. See Section 6@ Hazards.