Design and Optimisation of a Three Layers Thermal Neutron, Fast Neutron and Gamma-­ Ray Imaging System

The design and configuration of a multilayered imaging system with the ability to detect thermal
neutrons, fast neutrons and gamma rays has been
developed and its efficacy demonstrated. The work
presented here numerically determines the systems
efficiency and spatial resolution, using 252Cf and 137Cs as a
case study. The novelty of this detection system lies in the
use of small form factor detectors in a three-layer design,
which utilises neutron elastic scattering and Compton
scattering simultaneously. The current configuration
consists of 10 mm thick natural lithium glass (GS10)
scintillator integrated with a 20 mm thick plastic
scintillator (EJ-204) in the first layer, a 15 mm thick lithium
glass (GS10) scintillator in the second and a 30 mm thick
CsI(Tl) scintillator forming the final layer. Each of these
layers is backed with an 8 x 8 silicon photomultiplier diode
(SiPM) array. The overall size of the imaging system is 27
mm x 27 mm x 135 mm. MCNPv6.1 and Geant4-10.04 were
alternatively used to optimise the overall configuration and
to investigate detection modalities. Results show promising
performance with high precision source localisation and
characterization abilities. Measurements were virtually
obtained of two gamma-ray sources within steel enclosures
at angles of 15o
, 30o and 50o separation in order to test
spatial resolution ability of the system. With the current
active size of the system and the 8x8 SiPM configuration,
the results estimate the spatial resolution to be close to 30o
.
The ability of the system to characterise and identify
sources based on the type and energy of the radiation
emitted, has been investigated and results show that for all
radiation types the system can identify the source energy
within the energy range of typical reported sources in
literature.