Validation and calibration apparatus and method for nuclear density gauge

A cost effective, field-usable validation and calibration apparatus and method for nuclear density gauges comprises an absorption element, where the absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge. The absorption element may be positioned inside an enclosure, which also may include an insertion hole capable of receiving a source rod from a nuclear density gauge. The absorption element also can be capable of simulating a plurality of densities, both in backscatter and direct transmission modes. A method of validating and re-calibrating a nuclear density test gauge is also provided, where only a single block of a known density, either a reference block or a field block with a simulated density, is required.