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DETERMINATION OF MOISTURE CONTENT WITH A GAMMA BACKSCATTER DENSITY GAUGE
Author(s) -
CIFTCIOGLU O.,
BYATT D. A.,
TAYLOR D.
Publication year - 1972
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1972.tb01638.x
Subject(s) - water content , compton scattering , soil water , moisture , backscatter (email) , detector , physics , neutron , photon , content (measure theory) , analytical chemistry (journal) , optics , soil science , nuclear physics , environmental science , chemistry , mathematics , meteorology , chromatography , telecommunications , mathematical analysis , geotechnical engineering , computer science , wireless , engineering
Summary Gamma‐radiation, backscatter gauges, as normally employed for the determina‐tion of the bulk density of soils, use integral mode counting. They are relatively insensitive to the presence of soil moisture and hence not generally suitable for monitoring soil moisture content, particularly, if the soil type effect is minimized by counting only gamma‐photons of energy > 0.400 MeV for a 137 Cs source. However, using differential mode counting with the window set at about 0.08 MeV, the phenomenon is one of multiple instead of single scattering. With a source‐detector Separation of the order of 20 cm, about eight Compton in‐teractions are obtained and, as a multiplying factor of ZjA is involved at each interaction, the increased response with hydrogen‐containing material is easily observable. The value of Z/A for hydrogen is 1.0, and for materials not containing hydrogen about 0.5; therefore for water it is 5/9. Hence under these conditions, the response for water compared with non‐hydrogen‐containing materials is [(s/9)/(1/2)] 8 = 2.32 times, an increase of 132 per cent. This method can therefore be exploited to measure the moisture content of soils. The sensitivity is high, and the accuracy is better than ± 5 per cent, which is not as good as can be achieved with a separate thermal neutron detector, but is useful for many purposes and, of course, only one instrument is required.