How fixed nuclear gauges work
Industries make use of nuclear gauges for industrial gauging because they provide an inexpensive yet highly reliable and accurate method of measurement of thickness, density and make-up of a wide variety of materials or surfaces. There are two types of nuclear gauges, the fixed gauges and portable gauges that incorporate a sealed source containing a radioactive nuclear substance. In the fixed gauges, when the source’s holder shutter is opened, an invisible beam of radiation is directed at the material being measured. A detector which is located opposite the sealed source measures the radiation that passes through the material and registers the required information on a readout or connected computer. An example of industrial gauging is in a brewery where a nuclear gauge makes sure that each bottle contains the right amount of beer.
How portable nuclear gauges work
Portable nuclear gauges are used for industrial gauging in agriculture, construction and civil engineering for the measurement of the compaction of soil or the density of asphalt used in a paving mix. Two basic methods are used for measurement using portable gauges; backscatter method and direct transmission method.
- Industrial gauging through direct transmission - is more precise because it produces fewer errors in measurement of composition and compensates for surface roughness. During the measurement of soil density, a source rod is placed on a tube and inserted through a punched access hole beneath the surface of soil. Radiation is then transmitted from the source to a detector which is located on the base of the gauge. The radiation level at the detector will show the amount of soil compaction.
- Industrial gauging through backscatter method – when measuring the compaction of soil, an access hole is no longer necessary since the source rod and the detector can simply be placed on top of the surface. Radiation is directed beneath the surface where it is reflected back or scattered back to the to the gauge detector by the surface material. This method is also used to measure moisture content of a material using a neutron source or to measure material density through a gamma source. However, for density measurements, industrial gauging through backscatter method is less accurate than direct transmission due to the large scattering angle and the shallow depth of measurement although it is quicker and a lot easier. Backscatter method is good enough for measuring uniform materials like asphalt paving.