filtration, the wetting front moved deepest into the soil with the higher
initial water content. During the very early stages (0.5 hr) of infiltration,
the water content at the soil surface was highest in the soil with the
highest initial water content; however, with increasing time, the surface
water content approached the same ultimate value in all three soil col-
umns.


 C. Examples of Density Determination
 The single-energy gamma attenuation method has also been used to
measure the bulk density of several materials other than soils. Distribu-
tions of bulk density of wood measured along the diameter of the cross-
section of a 9-year-old tree and across a sample of marble are shown in
Figures 7 and 8, respectively, as examples of the utility of the gamma
ray attenuation technique (Ferraz, 26). In both cases a narrow gamma
beam of 60 KeV (241Am) with 1.6-mm diameter cross section was used.


E
U
0)



4,


co
Cr.


 S '1 2 3 4
 Radius of Trere Cross-Section, r(cm)

Figure 7. Distribution of wood density measured with distance across a disc
of Pinus elliottii (3.1 cm thick sample from a 9-year old tree) showing
growth rings (Ferraz, 26).