Nuclear density gauge
（重定向自Nuclear gauge）
A nuclear density gauge is a tool used in civil construction and the petroleum industry, as well as for mining and archaeology purposes. It consists of a radiation source that emits a cloud of particles and a sensor that counts the received particles that are either reflected by the test material or pass through it. By calculating the percentage of particles that return to the sensor, the gauge can be calibrated to measure the density and inner structure of the test material.