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NAA is divided into two catagories;

1. prompt gamma-ray neutron activation analysis (PG-
NAA), where measurements of gamma ray spec-
trum is taken place during irradiation,

2. delayed gamma-ray neutron activation analysis
(DGNAA), where the measurements of gamma
rays spectrum is taken place after irradiation.

There is common that where when one mentions NAA
it is generally refered to measurement of the delayed
gamma rays. Around 70% of the element can be de-
termined from NAA measurement. The sample is irra-
diated inside the reactor core. The sample has been
irradiated for short time. The instruments used for NAA
usually placed closed to where irradiation is made.

On the other hand, PGNAA is utilized neutron ex-
tracted from the reactor core by the beamport. In this
case, thermal neutron fluxes irradiated on sample is
very much less compared with the one in reactor core.
Since this is in-situ measurement, the detector for gamma
spectrum measurement is placed close to the sam-
ple. This will compansate the loss in sensitivity due
to fluxes. The size of sample used for PGNAA usu-
ally big because to obtain sufficient gauge volume to
ensure enough statistic of neutron counts.

Since neutron flux is very much less used in PG-
NAA and the gauge volume required is high, several
criteria is required to make PGNAA technique useful.

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