Dual Energy Gamma-ray Transmission for Coincident Measurement of Water Content and Dry Bulk Density of Soil

Nature ◽  
1967 ◽  
Vol 214 (5094) ◽  
pp. 1273-1274 ◽  
Author(s):  
B. D. SOANE
Keyword(s):  
Water Content ◽  
Bulk Density ◽  
Gamma Ray ◽  
Dual Energy ◽  
Energy Gamma

scholarly journals WATER CONTENT AND BULK DENSITY CHANGES IN A SOIL PEDON MEASURED WITH DUAL ENERGY GAMMA-RAY TRANSMISSION

1974 ◽  
Vol 54 (3) ◽  
pp. 325-328 ◽  
Author(s):  
R. J. REGINATO
Keyword(s):  
Water Content ◽  
Bulk Density ◽  
Gamma Ray ◽  
Soil Surface ◽  
Dual Energy ◽  
Transmission Technique ◽  
Density Values ◽  
Energy Gamma ◽  
Irrigation Levels ◽  
Water Contents

Water contents and bulk densities were measured in a soil pedon with a gamma-ray transmission technique utilizing 137Cs and 241Am. By alternating the sources for each scan down the soil profile, both bulk density and water content were determined in 1-cm increments in the top 10 cm of the pedon. Bulk density decreased to a depth of 6 cm about 30 min after 4 cm of water was ponded on the soil surface. As soon as the water drained from the surface, bulk density values increased and approached pre-irrigation levels. Water content increased rapidly corresponding to the decrease in bulk density. Assuming that the bulk density remains constant during ponding, calculated water contents may be in error by as much as 0.25 gcm−3.

Calculation of soil water contents from gamma ray readings

Soil Research ◽  
1964 ◽  
Vol 2 (1) ◽  
pp. 29 ◽  
Author(s):  
CG Gurr
Keyword(s):  
Water Content ◽  
Bulk Density ◽  
Soil Water ◽  
Gamma Ray ◽  
Initial Conditions ◽  
Large Numbers ◽  
Field Samples ◽  
Water Contents ◽  
Soil Water Contents

A method is given for calculating water contents of a column of soil from gamma ray data. The method is particularly useful for undisturbed field samples of unknown initial conditions. Values of water content and bulk density determined at the end of an experiment are used for calibration. To aid the calculation of large numbers of results, a nomogram has been constructed.

A dual source gamma ray traversing mechanism suitable for the non-destructive simultaneous measurement of bulk density and water content in columns of swelling soil

Soil Research ◽  
1973 ◽  
Vol 11 (1) ◽  
pp. 83 ◽  
Author(s):  
BJ Bridge ◽  
N Collis-George
Keyword(s):  
Water Content ◽  
Bulk Density ◽  
Gamma Ray ◽  
Single Channel ◽  
Soil Column ◽  
Pulse Height ◽  
Silica Sand ◽  
Absorption Coefficients ◽  
Mass Absorption ◽  
Pulse Height Analyser

A traversing mechanism is described in which 100 mCi sources of americum-241 and caesium-137 are alternately brought into line with a sodium iodide (thallium) scintillation counter connected to a single-channel pulse height analyser equipped with two preset base lines. The equipment is capable of scanning a 10 cm diameter soil column equipped with sensors to a height of 200 cm, and facilities are provided for automatic indexing at preset intervals to an accuracy of 0.01 cm. Non-linear counting losses in the spectrometer system are described, and were found to be dependent on the window setting of the pulse height analyser. With the window setting adjusted to cover the apparent spread of the gamma peak, counting losses were negligible. Mass absorption coefficients of various materials were obtained using a compartmented box. Measured mass absorption coefficients of water, silica sand, and a chernozemic soil were 0.201, 0.247, and 0.303 cm2 g-1 respectively for americum-241, and 0.0826, 0.0746, and 0.0728 respectively for caesium-137. The precision of the apparatus was demonstrated by determining the moisture characteristic and bulk density characteristic of 0.5-1.0 mm aggregates of Narrabri soil during absorption and desorption. Gamma ray attenuation measurements and direct volumetric measurements were comparable. The standard deviations in the gamma ray measurements were found to be 0.03 g cm-3 for bulk density and 0.04 cm3 cm-3 for water content. Most of this inaccuracy arose from lack of precision in the americum-241 mass attenuation coefficient for the soil. By contrast, changes in moisture content and bulk density, at any level, of 0.004 cm3 cm-3 and 0.004 g cm-3 respectively, were statistically very significant.

Use of neutron and gamma radiation meters to estimate bulk density and correct for bias of sampling for water content in a swelling clay soil

Soil Research ◽  
1988 ◽  
Vol 26 (2) ◽  
pp. 261 ◽  
Author(s):  
AS Hodgson
Keyword(s):  
Water Content ◽  
Bulk Density ◽  
Gamma Ray ◽  
Clay Soil ◽  
Soil Depth ◽  
Three Dimensional ◽  
Sampling Bias ◽  
Relative Difference ◽  
Undisturbed Soil ◽  
Shrinkage Cracks

Two radiation methods were used to estimate the bulk density of a three-dimensionally swelling grey clay soil used for furrow irrigation at Narrabri, N.S.W. Firstly, gamma ray scattering was calibrated with measurements of wet bulk density derived from undisturbed soil cores. Secondly, a high correlation between neutron counts and gravimetric water content in this soil provided a basis for predicting bulk density corrected for bias in sampling of shrinkage cracks by using a published theoretical model of three-dimensional soil shrinkage. Gamma ray backscattering was poorly correlated with wet bulk density (�w), possibly because dry bulk density and water content are negatively correlated in swelling soil, which restricted �w to a relatively narrow range of values. This technique is therefore not recommended for use in this soil. High correlation (0 82 < r < 0.98, all P < 0.001) between neutron counts and bulk density corrected for three-dimensional shrinkage was found at all soil depths between 0.1 and 1.5 m. A precision of k0.01 Mg m-3 required from three to six samples per mean, depending on soil depth. The mean relative difference between predictions of bulk density from neutron counts compared with independent estimates by the core method was <4.1% at depths below 0.3 m. The recommended procedure is therefore to predict bulk density from neutron counts in order to correct for sampling bias and bulk density effects associated with the neutron attenuation method. The method eliminates the need for additional sampling for bulk density in conjunction with the neutron moisture meter in soils that shrink and swell three-dimensionally. However, the method is not appropriate for detecting differences in bulk density between soils with different structure unless the constants used in the model and the shrinkage behaviour are known for each soil. The latter requirements would usually preclude the technique for this purpose. At low water contents near the permanent wilting point for cotton, neutron escape through shrinkage cracks did not cause problems at depths below 0.3 m. The neutron method should therefore be appropriate for use at depths below 0.3 m in dryland hydrological studies in this soil.

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