The TRIGA Mark II reactor in Malaysia (MINT) has the same function as the Oregon State TRIGA
Reactor (OSTR) in Corvallis Oregon. The MINT is used as an educational facility and irradiation
facility with similar test capabilities as the OSTR such as neutron activation analysis (NAA),
prompt gamma neutron activation analysis (PGNAA) , as well uses for radiography and boron
neutron capture therapy (BNCT). The MINT reactor also utilizes the same low enriched fuel
(LEU) at the same prescribed weight percent as the OSU TRIGA, operating under the same
pulsing and steady state conditions such as 1 MWth at steady state.
The article discusses the details of calculating the thermal to epithermal neutron flux ratio, the
epithermal shape factor and compactor factor. This is important when considering the
concentration of a sample using a standardization method in NAA. To identify these
parameters, they used what is called a “bare triple monitor method using K0 factors”. This
procedure is implemented as a testing for quality assurance and to develop a standard
deviation for null data. The use of certified nuclear reference material is irradiated as the
control for these types of experiments.
The test material of Au/Zr, and the control material Al/Au, were both irradiated at specific
fluxes and time intervals and then measured at reference position. The use of gamma
spectrometry with an n-type High Purity Germanium detector (HPG) was used to compute the
parameters of thermal to epithermal neutron flux ratio, the epithermal shape factor and
compactor factor. The data was then run through several computational codes in order to gain
effective solid angle and elemental concentration.
A table of results was reported from the experiment providing values for the thermal to
epithermal neutron flux ratio, the epithermal shape factor and compactor factor. Error analysis
concluded that the results were fair, but the reasoning for predicted discrepancies involving
items such as core configuration, burn up of fuel assemblies, and pressure drops in one and
two–phase flow areas were among the parameters that may cause fluctuation.
The article concluded that thermal neutrons have the dominate effect in neutron activation
with thermal neutrons causing the most reactions and the reaction rate being proportional to
the neutron flux. The article also highlights the need for accurate thermal to epithermal
neutron flux ratio, epithermal shape factor and compactor factor calculations in every
The neutron activation analysis is a very powerful and sensitive technique for
identifying characteristics of many elements and that’s by performing both
qualitative and quantitative analysis of major, minor, and trace elements in
samples from almost every conceivable field of scientific or technical interest .
In neutron activation analysis technique, a sample is irradiated by thermal
neutrons so as a result of irradiation, it becomes radioactive. The sample and their
relative concentrations can be identified by measuring the positive and negative
βs, Js, and half-life of the activated sample. The Industrial activation analysis is
usually done with thermal neutrons from a reactor, where the accelerator with fast
neutron fluxes of ~1010 neutrons/cm2/s or with neutron flux can be as high as
~1013 neutrons/cm2/s .
When the activation analysis is compared to other instrumental analytical methods
like gravimetric, calorimetric, spectrographic, or mass spectroscopy, it is found
that the sensitivity of the activation analysis is usually shown to be better over a
factor of 10 than other methods. Activation analysis is used extensively in such
fields as geology, medicine, agriculture, electronics, metallurgy, criminology, and
the petroleum industry .
After irradiation, the sample is transferred immediately to the high purity germanium
(HPGe) detector, and a spectrum is accumulated for a time, (t1), long enough to get
reasonable statistics under the photo peak. The time is usually at least one half-life. The
true number of disintegration, (Nd) that occurred during t1 can be determined from the
following equation .