It is a quick method of determining the in-situ density of soils based on irradiation.


Special equipment is used for this test which measures the density using gamma radiation. The gauge usually has a small gamma source (about 10 mCi) such as cesium-137 on the end of a retractable rod.

atomic density gauge
Atomic Density Gauge – used for in situ density measurement of soil


  1. Create an even surface using a guide plate or any other suitable tool.
  2. Make a hole by fastening a steel rod of the same diameter as the retractable gauge rod. The hole should be at least 50 mm deeper than the intended depth of measurement.
  3. Nuclear density gauges generally operate in two modes.
    1. direct transmission
    2. back scatter
  4. To measure soil density, set the instrument to ‘Direct Transmission Mode’.
  5. Lower the source rod into the hole. Set the handle to the required depth position.
  6. Read the detector count on the panel. Use the calibration chart provided by the manufacturer to obtain the density of the material.
  7. It may be noted that the detector number is inversely proportional to the density of the surrounding material.

pay attention

The nuclear density gauge is calibrated in the factory. Since the source material undergoes decay, it needs to be calibrated from time to time as per the procedure given by the manufacturer.

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.