Neutron moisture gauge

A neutron moisture meter is a moisture meter utilizing neutron scattering. The meters are most frequently used to measure the water content in soil or rock. The technique is non-destructive, and is sensitive to moisture in the bulk of the target material, not just at the surface.

Water, due to its hydrogen content, is an effective neutron moderator, slowing high-energy neutrons. With a source of high-energy neutrons and a detector sensitive to low-energy neutrons (thermal neutrons), the detection rate will be governed by the water content of the soil between the source and the detector. The neutron source typically contains a small amount of a radionuclide. Sources may emit neutrons during spontaneous fission, as with californium; alternatively, an alpha emitter may be mixed with a light element for a nuclear reaction yielding excess neutrons, as with americium in a beryllium matrix.

References

Visvalingam, M.; Tandy, J. D. (1972). "The Neutron Method for Measuring Soil Moisture Content-A Review" (PDF). Journal of Soil Science. 23 (4): 499–511. doi:10.1111/j.1365-2389.1972.tb01680.x.
Pershin, A. A.; Glushkova, L. T. (1980). "Nomenclature and design principles of neutron moisture meters and means of calibrating them". Measurement Techniques. 23 (4): 348–351. doi:10.1007/BF00831296. S2CID 121099209.
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Lowenthal, Gerhart C; Airey, P. L (2001-08-27). Practical applications of radioactivity and nuclear radiations: an introductory text for engineers, scientists, teachers and students. p. 217. ISBN 978-0-521-55305-6.
Kirda, C.; Reichardt, K. (1992). "Comparison of neutron moisture gauges with nonnuclear methods to measure field soil water status". Scientia Agricola. 49: 111–121. doi:10.1590/S0103-90161992000400015.
Nagpal, M K; Mehta, P P; Nagpaul, K K; Rama (1973). "Characteristics of a neutron moisture gauge with a solid state detector". Pramana. 1 (2): 112. Bibcode:1973Prama...1..112N. doi:10.1007/BF02847186. S2CID 121603277.
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