"Directionally Sensitive Neutron Detector For Homeland Security Applications,"
M.S. Thesis, Nuclear Engineering, Texas A&M University, College Station, TX (2011).
With an increase in the capabilities and sophistication of
terrorist networks worldwide comes a corresponding increase in the
probability of a radiological or nuclear device being detonated
within the borders of the United States. One method to decrease the
risk associated with this threat is to interdict the material
during transport into the US. Current RPMS have limitations in
their ability to detect shielded nuclear materials. It was proposed
that directionally sensitive neutron detectors might be able to
overcome many of these limitations. This thesis presents a method
to create a directionally sensitive neutron detector using a unique
characteristic of 10B. This characteristic is the Doppler
broadening of the de-excitation gamma-ray from the 10B(n, alpha)
reaction. Using conservation principles and the method of cone
superposition, the mathematics for determining the incoming neutron
direction vector from counts in a boron loaded cloud chamber and
boron loaded semiconductor were derived. An external routine for
MCNPX was developed to calculate the Doppler broaden de-excitation
gamma-rays. The calculated spectrum of Doppler broadened
de-excitation gamma-rays was then compared to measured and
analytical spectrums and matched with a high degree of accuracy.
MCNPX simulations were performed for both a prototype 10B loaded
cloud chamber and prototype 10B loaded semiconductor detector.
These simulations assessed the detectors' abilities to determine
incoming neutron direction vectors using simulated particle
reactant data. A sensitivity analysis was also performed by
modifying the energy and direction vector of the simulated output
data for 7Li* particles. Deviation coefficients showed a respective
angular uncertainty of 1.86 degrees and 6.07 degrees for the boron
loaded cloud chamber and a boron loaded semiconductor detectors.
These capabilities were used to propose a possible RPM design that
could be implemented.
Associated Project(s):SHIELD (Smuggled HEU Interdiction through Enhanced anaLysis and Detection): A Framework for Developing Novel Detection Systems Focused on Interdicting Shielded HEUDirection Sensitive Neutron Detectors for Border Monitoring