An effective method for measuring water velocity in an aerated zone has been developed by means of fast neutron transmission. Velocity υ, can be determined from the derived equation υ=
a•(tan φ)/(
No-
N1), where
a is the detection width of transmitted fast neutron, tan φ is decrement of the detected counting rate, and
No and
N1 are counting rates before and after infiltration in the soil layer, respectively. When
252Cf (273 μCi) is used for the fast neutron source and NE-213 liquid scintillator (2“φ×2”
l) is used for the detector in the experiment, the result obtained indicates that this method gives an accuracy within 10% error for a column diameter of 3_??_40cm at an arbitrary depth. In addition the method is found to be more sensitive for a large diameter column than for a small one.
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