"Passive Neutron Detection in Ports for Homeland Security Applications,"
M.S. Thesis, Texas A & M University, May 2013.
The smuggling of special nuclear material (SNM) has long
been a concern. In April 2009, President Obama declared that a
terrorist acquiring a nuclear weapon was the most immediate threat
to global security. The Second Line of Defense (SLD) initiative was
stood up by the National Nuclear Security Administration to deter,
detect, and interdict illicit trafficking of nuclear and
radioactive materials across international borders and maritime
shipping. The SLD initiative does not provide for the detection of
SNM being carried on small, personal watercraft. Previous work
examined the possibility of using active neutron detectors to
induce fission in SNM and detect the response. This thesis examines
the possibility of detecting SNM using passive 3He neutron
detectors. Monte Carlo N-Particle (MCNP) simulations were run to
determine the best detector configuration. Detecting sources at
increasing depths, detecting moving sources and the effects of
waves were also simulated in MCNP. Comparisons with experimental
measurements showed that detectors parallel to the surface of water
were best at detecting neutron sources below the surface.
Additionally, stacking detectors and placing a cadmium sheet
between the polyethylene blocks resulted in a greater ability to
determine the height of a source by taking the ratio of count rates
in the lower and upper detectors. Using this configuration, a
source of strength 3.39 x 10^5 n/s could be detected to a depth of
12.00 in below the water surface. Count rates in the presence of
waves did not average out to count rates taken above a flat plane
of water. Detectors closer to the water performed worse than above
a flat plane while detectors placed higher recorded more counts
than above a flat plane. Moving sources were also simulated;
sources under water, 3.00 ft from the detectors, and moving at 5.8
kts could be detected above background.
Associated Project(s):SHIELD (Smuggled HEU Interdiction through Enhanced anaLysis and Detection): A Framework for Developing Novel Detection Systems Focused on Interdicting Shielded HEU