Page 57 - bukuneutron

2.7.2 Management of a Neutron Moisture
Gauge

1. Measurement of soil moisture can be done at
temporary or permanent sites. Both sites shall
be equipped with access well tube in the soil to a
depth deeper than the maximum calibrated mea-
surement coverage. A small gap between ac-
cess tube and soil cannot be avoided, but water
should not flow down the side of the access tube.
Cover the top of the access tube between mea-
surements to prevent water, reptiles, animals, and
other foreign material get into the well tube.

2. Access tube is made by aluminum pipe with as-
sociate diameter depending on the moisture probe
geometry. For multiple sites, it is suggested to
use the same material for each site. Aluminum is
considered transparent to thermal neutrons there-
fore give affects the readings the least. Aluminum
is considered the best, but it is expensive com-
pared to PVC, clay pipe or other types of tubes.

3. PVC pipe are also commonly used for making ac-
cess tubes. This material is gives some effect on
the absorbing of thermal neutrons. There it will
affects the readings because thermal neutrons
are absorbed by chlorine and hydrogen in PVC.
Efficiency reduces significantly and it is not eco-
nomical compared with aluminum.

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