Abstract
Special Nuclear Materials (SNM) located aboard ships emit radiation that may be detectable in the undersea environment. An Unmanned Underwater Vehicle (UUV) could be equipped with detection capabilities to determine whether commercial or private vessels are carrying SNM prior to reaching port. Additional research is needed improve such a UUV’s ability to detect and discriminate between types of SNM and reduce false- positive detections. This research builds on past work by C. T. McKay to provide a higher fidelity characterization of detectable radiation signatures from SNM in the undersea environment with a focus on plutonium-bearing SNM. 252Cf will be used to produce a similar neutron energy distribution as plutonium. A carbon steel plate will simulate the effect of vessel structural materials to produce representative neutron and capture gamma radiation profiles. The transport of both neutron and capture gammas is considered and compared. The neutron signature is reduced due to absorption in seawater. However, neutron capture by seawater produces high-energy gammas. These high-energy capture gammas are not attenuated as significantly as neutrons, have a distinct energy profile, and may be readily detected at longer distances in seawater. A Sodium Iodide detector and a High Purity Germanium detector will detect the gamma population at set distances from the source and this signature will be compared with the neutron signature detected with a Helium-3 detector. The results will provide insight into preferable methods of detection and discrimination of capture gamma signatures to
identify SNM in the maritime environment.
Included in
A Characterization of Undersea Neutron and Capture Gamma Signatures Resulting From Special Nuclear Material on a Maritime Vessel
Purdue
Special Nuclear Materials (SNM) located aboard ships emit radiation that may be detectable in the undersea environment. An Unmanned Underwater Vehicle (UUV) could be equipped with detection capabilities to determine whether commercial or private vessels are carrying SNM prior to reaching port. Additional research is needed improve such a UUV’s ability to detect and discriminate between types of SNM and reduce false- positive detections. This research builds on past work by C. T. McKay to provide a higher fidelity characterization of detectable radiation signatures from SNM in the undersea environment with a focus on plutonium-bearing SNM. 252Cf will be used to produce a similar neutron energy distribution as plutonium. A carbon steel plate will simulate the effect of vessel structural materials to produce representative neutron and capture gamma radiation profiles. The transport of both neutron and capture gammas is considered and compared. The neutron signature is reduced due to absorption in seawater. However, neutron capture by seawater produces high-energy gammas. These high-energy capture gammas are not attenuated as significantly as neutrons, have a distinct energy profile, and may be readily detected at longer distances in seawater. A Sodium Iodide detector and a High Purity Germanium detector will detect the gamma population at set distances from the source and this signature will be compared with the neutron signature detected with a Helium-3 detector. The results will provide insight into preferable methods of detection and discrimination of capture gamma signatures to
identify SNM in the maritime environment.