Nuclear density gauges consist of a sealed source in a source holder and a scintillation detector. The source holder is mounted on a side of a pipe with the detector on the opposite side. A focused beam of radiation is transmitted from the source through the pipe and process material to the detector. As the density of the material in the pipe changes, the amount of radiation reaching the detector changes. The greater the density of the material, the lower the radiation field at the detector. Process density is provided in the form of a current output.