This
technique is based on the unique moderating effect that hydrogen atoms
have on the energy level of neutrons. Simply put - a source of high
energy neutrons is placed against the vessel. Hydrogen atoms inside
moderate these to low energy or thermal neutrons which can be readily measured
with sensitive detectors.
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Exploiting this property is extremely useful
in that access need only be to one side of the vessel. This makes
it very quick. It is also accurate with a tolerance typically ±1
inch.
The neutron backscatter technique not only
determines liquid/vapor and solid vapor interfaces, but also in some instances,
successfully locates liquid/liquid and liquid/solid interfaces. Typical
applications include:
-
Determining liquid in distillation column
downcomers and draw pans
-
Level measurements during service or repair
of installed gages.
-
Calibration of nucleonic or conventional level
gages on storage tanks, spheres, and tank cars.
-
Measurements of levels in vessels not requiring
monitoring such as knock out pots and heat exchanger shells
-
Locating sludge levels in the bottom of tanks
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