ut 3.2
0)
C



 S0 5 10

 Thickness of Marble Sample, y(cm)

Figure 8. Distribution of density measured with distance across a piece of
white marble 2.8 cm thick.

In Figure 7, nine annual growth rings are clearly distinguishable from
the distributions of bulk density of the wood along the diameter of the
cross section. Depressions on the curve of bulk density correspond to
the rapid growth of the wet summers (normally with high rainfall) of
Brazil and peaks in the curve correspond to slower growth rates during
the relatively dry winter months. The bulk density of the wood has an
average value of approximately 0.5 g/cm3. Such distributions of the
density of wood in trees can be compared with long term weather data
for evaluations of the influence of climate upon the growth of trees in
commercial forests.



VII. Dual-Energy Method for Simultaneous Determinations
 of Soil Water Content and Bulk Density
 A. General Considerations
 The simultaneous measurement of water content and bulk density
using the dual-energy gamma attenuation method requires good resolu-
tion, precise values for water and soil mass attenuation-coefficients for
both energies, precise measurement of the thickness of the soil sample,
and accurate measurements of the beam intensities for both energies.
 For the dual-energy gamma attenuation method, there are at least two
commonly used ways to measure the radiation intensities for the two