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Model 3440
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5
M
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The Model 3440 gauge uses a 40 mCi (1.48 GBq)
Americium-241:Beryllium neutron source to measure the
hydrogen content (consequently the water content) of the
material.
Neutrons emitted by the Am-241:Be source penetrate the
material and are
thermalized
(or slowed).
Thermalization
is the
process where neutrons are slowed to the point where further
collisions with hydrogen or other materials will not continue to
slow the neutron.
The Model 3440 gauge contains a helium-3 neutron detector
that is sensitive to thermalized neutrons. This detector is
insensitive to non-
thermalized or “fast” neutrons and, as a
result, the counts obtained are directly proportional to the
amount of hydrogen/moisture present in the material.
The
depth of measurement
, or depth at which 98% of the
counted neutrons pass before reaching the detector, is a
function of moisture content:
Depth (in.) = 11
–
(0.17
u
M), where: M = moisture in pcf
or
Depth (mm) = 280 - (0.27
u
M), where: M = moisture in kg/m
3
Therefore, the higher the moisture content in the material being
measured, the smaller the depth of measurement. The
normalized curve set shown in Figure 5 illustrates the effect of
moisture content on the depth of measurement.
Содержание RoadReader 3430
Страница 14: ...1 6 Figure 1 Model 3440 Gauge and Accessories...
Страница 19: ...Model 3440 2 3 Figure 2 Direct Transmission Geometry Figure 3 Backscatter Geometry...
Страница 20: ...2 4 Figure 4 Backscatter Surface Density Effects Top Layer Effect Curves...
Страница 22: ...2 6 Figure 5 Effect of Moisture on Depth of Measurement...
Страница 164: ...F 2 STANDARD COUNT LOG Gauge Serial Number _____________ Date MS DS Date MS DS...