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of hydrogen atom. The point where gives the signifi-
cant changes in the back-scattered signal indicates the
starting layers of different material. Therefore, the pro-
file of back-scattered signal provide information of the
level of each layer and the large count indicates the
concentration of hydrogen in each layer.

2.4 Applications in Interface measure-
ment

As explain in previous Sections, there is significant changes
in the back-scattered signal within the border of each
layer and abrupt changes at the layer interface. This
phenomenon revealed information of liquid-liquid inter-
face or liquid-vapor interfaces. Interface of material
phases indicate by the abrupt changes in the back-
scatter signal. Vapor has less concentration of hydro-
gen atom will scatter less neutrons compared with the
organic.

Lets imaging when the back-scatter gauge is moved
from the top to the bottom of the storage tank. The sig-
nal of back-scattered neutron increased sharply at the
vapor-organic interface. Similar process happened at
the interface of organic and water where the sharp in-
creased of back-scattered signal when the gauge move
over the region containing water. Inverse phenomenon
can be seen when the gauge move down the zone in

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