Detecting nuclear materials smuggling: using radiography to improve container inspection policies

Abstract

This paper proposes a layered container inspection system for detecting illicit nuclear materials using radiography information. We argue that the current inspection system, relying heavily on the Automated Targeting System (ATS) and passive radiation detectors, is inherently incapable of reliably detecting shielded radioactive materials, especially highly enriched uranium (HEU). This motivates the development of a new inspection system, which is designed to address a fundamental flaw of the ATS-based system, allowing for improved defense against sophisticated adversaries. In the proposed inspection system, all cargo containers go through x-ray imaging equipment first. From the x-ray image, a hardness measure of the container is computed. This hardness measure characterizes how likely it is that shielded HEU, if it does exist in the container, will not be detected in a subsequent passive detection step. Depending on the value of the hardness, the lower-hardness containers are sent to passive detection and the high-hardness containers are sent directly to active detection. This paper explores the trade-off between the detection probability of the new inspection system and the expected sojourn time a container spends in the system. The solution details and decision-making tools for using such a system are provided. Comparisons are made between the proposed system and the current ATS-based nuclear inspection system.

Detecting Nuclear Materials Smuggling: Performance Evaluation of Container Inspection Policies

“…In this article, we seek to eliminate this weakness by proposing a hybrid system that combines the use of both radiography imaging and the ATS system. Another major difference is that in Gaukler et al , ( 9 ) the objective of the inspection policy optimization is to maximize a weighted average of detection probabilities for different container types. Such an objective formulation makes it potentially easier for adversaries to game the system if they are able to select a container type that has a low detection probability (DP).…”

“…This gives assurance that independent of the adversaries’ gaming abilities, the lower bound on DP is maximized. Finally, in our current model we allow for container‐type‐specific false alarm rates, whereas in Gaukler et al , ( 9 ) there was a single false alarm rate applied to all containers types.…”

“…The HCS inspection policy is a refined version of the model described and analyzed in Gaukler et al ( 9 ) Fig. 3 shows the flow diagram for this system.…”

Interdiction Models and Applications

“…Wein et al [73] propose improvements to an existing spatial deployment of RPMs at a foreign port to increase effectiveness of the system without increasing congestion. Gaulker et al [27] and Wein et al [74] both employ queueing network models to characterize congestion in a multi-layered security system at a seaport, and they seek to optimize the inspection strategy, understanding the tradeoff between detection probability and congestion. For further work on inspection strategies at a single port, see [14,40,42,67].…”

Shielded radiography with a laser-driven MeV-energy X-ray source

“…Passive technologies are a common method for SNM detection, and function by detecting radiation signatures emitted by SNM. However, certain SNM, such as highly enriched uranium, can be easily shielded to defeat passive detection [4].…”