coefficient for the solution may be different from that of pure water. For
example, iron in solution can increase significantly the mass attenua-
tion coefficient for water. A 0.5 M solution (0.076 g/cm3) of FeSO4
increases the ft water value by 12%, and this increase of / is propor-
tional to the concentration.
 In order to test the dual-energy gamma method for determining water
content and bulk density, two experimental procedures were performed.
These are described in the following sections.


 1. Sensitivity of the Method for Determinations for
 Soil Water Content
 Ferraz (26) used two widely different soils to obtain the sensitivity
 of the method for determination of 0: a Red soil (sample No. 2 in Table



 n 10o: 10 bf





 a I I'' -[ ,
 0 10 10 l


 L L
 > >
 Po
 4 '- -3 ~-






 L L

 10 -6

 10 10S 10 10 u'

 Precision of Attenuation Coefficients (cm2/g)

 Figure 9. Dependence of standard deviations in measurements of soil bulk
 density and water content upon precision of measurement of 60 and 662
 KeV mass attenuation coefficients for soil and water.
 29