The gauge consists of a radiation source that emits radioactive particles and a sensor that counts the received particles. By calculating the percentage of particles that return to the sensor, the gauge can be calibrated to measure the density of the test material. This service is used by construction companies, contractors and civil engineers.
How is it done?
The gauge is operated in one of two modes, backscatter or direct transmission. In backscatter mode, which is mainly used for determining the density of freshly laid bituminous material, the source rod is lowered so that it remains within the gauge. The source emits gamma rays which interact with electrons in the material and lose energy and/or are redirected (scattered). Gamma rays that are scattered towards the receiver are counted. The higher the density of the surfacing material the higher the probability that a gamma ray will be redirected towards the detector. A calibration factor is used and internal software calculates the density of the material.
In direct transmission mode the source rod is lowered into a preformed hole in the material to be tested. The source rod emits gamma rays, which then interact with electrons in the test material and lose energy and/or are redirected (scattered). Gamma rays that lose sufficient energy or are scattered away from the detector are not counted. The higher the density of the material, the higher the probability of interaction and the lower the detector count. Therefore, the detector count is inversely proportional to material density. Again as with backscatter mode a calibration factor is used and internal software calculates the density of the material.
How long does it take to get the results?
The test is carried out to give the client an immediate indication on site of the density and moisture content of the material being tested. Invaluable information when for instance you are laying hot asphalt.