A nuclear density gauge includes a base and at least one gamma radiation detector mounted at a predetermined location relative to an axis extending longitudinally of the base. The gauge further includes a gamma radiation source and a source mount that mounts the gamma radiation source for movement along a path between an active first position located at a first longitudinal distance from the detector and an active second position located at a second longitudinal distance from the detector. In this way, gamma radiation is detected emanating from the source and backscattered from the underlying material sample through a first path of travel when the source mount is at the first active position and through a second path of travel when the source mount is at the second active position. The source mount may also move the source from the active first and second positions to an inactive third position shielded by gamma radiation shielding material.