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How it Works: Density Testing Using a Nuclear Density Gauge

By March 29, 2023No Comments3 min read

Nuclear density testing is a method used in road or construction projects, wind or solar power generation construction sites, residential and commercial construction sites, mining operations, agricultural and forestry settings, and even for archaeology purposes, to measure the density and inner structure of soil or asphalt.  A nuclear density gauge is a testing device that uses low level radiation to measure the wet density, dry density, and moisture content of soil and granular construction materials.

Testing of compacted soil is very important, as the test will verify that the soil conditions are suitable to support structures, streets, highways, etc. Improper compaction can lead to serious problems.  Over time, the soil may settle or slide, allowing water to pass underneath, which in time may lead to erosion and could cause damage to building foundations.  Likewise, improper compaction in roads could result in the settling of pavement and cracking of pipes beneath the road.

The nuclear density gauge (sometimes referred to as a “Troxler” after major manufacturer Troxler Electronic Laboratories) is comprised of a gamma radiation source (such as Cesium-137) about the size of a pebble at the end of a source rod, and Geiger Mueller tubes embedded in the base at the other end of the gauge. The source rod is lowered into the ground and, once released from its shielded housing, gives off just enough radiation to measure density. The Geiger Mueller tubes detect the gamma radiation that is emitted from the radiation source and passes through the material under the gauge. 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.

Some advantages to using a nuclear gauge to measure soil samples are that the tests are very quick and only take a few minutes to perform.  This makes nuclear density testing the optimum method for large projects, which may require many tests per day, and it can be used on a wide range of soil types.  Some disadvantages are that the testing equipment is very expensive and can be sensitive in harsh environments, and, because radiation is involved in the testing, personnel are required to wear dosimeter badges to measure their exposure to radiation.

Most states require the operator of the nuclear density gauge to be certified, and that the device be maintained and stored in a safe manner.  Operator certification can be obtained by completing training in the theory (written exam) and use of a nuclear gauge (practical exam).  In New York State, for example, there are specific guidelines relating to how the gauge is to be stored when not in use, protocol for testing procedures and supervision of technicians, and notification to local first responders that there is a radiation source onsite.

Many of Encorus Group’s technicians are certified to perform nuclear density testing.  For more information about this service, visit our website at or call Jeremy Lake at 716.592.3980, ext. 133.