English abstract
The development and optimization of a dual gamma-neutron imaging system
can offer significant advancement in the industrial field in general and in
the nuclear security field in particular as special nuclear materials (SNM)
sources of interest emit both particle types. In this study a multi-layered,
portable, real-time, dual gamma-neutron imaging system that maps thermal
neutrons, fast neutrons, and gamma-ray photons has been optimized using
Geant4 Monte Carlo simulations toolkit. The current design allows the system
to image, localize and characterize a wide range of radioactive sources and
special nuclear materials (SNM). This project will looks at enhancing the
current design in three different areas.
First area of enhancement was examine the (EJ-212) plastic scintillator detector
as a potential replacement for (EJ-204) plastic scintillator in the first layer. It
was found that it possesses a low mass attenuation coefficient and a compton
scattering probability of less than 15% for gamma energies exceeding 1 Mev.
Second area of enhancement was Simulations were conducted using four
radioactive sources 252Cf, 235U, 137Cs and 60Co to test different separation
distances between the three layers of the system. The results showed that
the increase in the separation distance by a few centimeters does significantly
impact the detection efficiency of gamma and neutrons rays. Finally, the
external system shield was tested as the third area of enhancement. The
investigated design included two different materials: Stainless steel and
Polyethylene. The results show that when a 3 mm layer of stainless steel
was coated with an additional 3 mm layer of Polyethylene, the background
radiation noise was at its minimum.
