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where neutron source-detector gauge is placed
in the proper shielding container where the in-
fluence from external neutron is eliminated. The
trend of count ratio should be recorded and anal-
ysed regularly. Count statistic with at least around
five counts are recommended for calculating the
average standard count to ensure error in the
count ratio is minimised.

10. Air Gaps: Air gaps between soil and access tube
is difficult to eliminate. The gaps itself is not greatly
affect the neutron count rate but the water can
flow and filling the gaps. The water in the gap
can affect the neutron count rate. Other possi-
bility that can cause high neutron rate is the ex-
istance of sand around the access tube. Solidify
clay can be used to fill the air gaps and minimise
flow of water surrounding the access tube. Oth-
erwise, the area with high potential of water to
flow should be avoided.

2.8 Summary

This chapter discuss the principle, applications and some
pros and cons of the neutron back scatterred tech-
nique for moisture measurement in oil and gas indus-
tries, hydrology,agriculture and civil engineering. There
are still some others but not discuss in this chapter.

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