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gamma in long time. The temperature inside the irra-
diation channel is about 40°so that not able to make
plastic material soften when exposed to a short pe-
riod.The wall thickness of plastic should not be so thick
other wise some thermal neutrons will absorb by the
wall itself. The activation of plastic also almost negli-
gible and it is safe to be used several times.

3.4 Sample preparation

Sample for NAA usually can get from many forms and
types. There are seveal common criteria in preparing
the sample for neutron irradiation in the reactor core.
Top most important criteria is for ensure safety of reac-
tor core and safety of the worker. Each sample has to
be investigated properly by the expert in reactor neu-
tronic before let into the reactor core. This is important
point to ponder because, in sample that can change
reactivity of reactor core is not allowed.

Detail information of the elements contain in the
object sample is crucial with respect to the engineer-
ing and physics neutronic of reactor. However, user
usually does not has an idea about the elements that
makes the sample before irradiation. But, user is re-
sponsible to provide at least the most possible element
contain in the sample. In addition, the exact weight of
each sample also should be measured and provided
by the owner of the sample.

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