Page 48 - bukuneutron

ness of acrylic sheets. Acrylic is chosen because the
density and hydrogen content is almost equivalent with
the water. It is also solid so that easy to determine the
thickness compared with the water itself.

The calibration is done using neutron moisture gauge,
where it is positioned at the top of set of acrylic plates
with the same physical and mechanical properties such
as thickness and materials composition. The back scat-
tering phenomenon for each thickness of water is cal-
ibrated by adding one sheet of acrylic plate on to the
another set of acrylic plates. Every time adding the
acrylic sheet under the gauge is actually simulate the
increase in thickness of water in between the gap un-
der the storage tank floor. Eventually, the desired cali-
bration curve consists of water thickness as well as the
gap information is obtained.

2.6 Measurement of Soil Moisture

Moisture in soil is crucial for many situations, for exam-
ple soil in an agriculture area and soil in construction
area. Soil moisture meters based on the radioactive
sealed neutron source for measuring humidity of soil
used in a civil engineering construction or in a farm-
ing area consists several peripheral. It should con-
tain an electronic gauge, a connecting cable, and a
source tube containing both neutron source and de-
tector tube. An access tube is installed in the ground,

35