Interdicting nuclear material on cargo containers using knapsack problem models

Abstract

This paper introduces a framework for screening cargo containers for nuclear material at security stations throughout the United States using knapsack problem, reliability, and Bayesian probability models. The approach investigates how to define a system alarm given a set of screening devices, and hence, designs and analyzes next-generation security system architectures. Containers that yield a system alarm undergo secondary screening, where more effective and intrusive screening devices are used to further examine containers for nuclear and radiological material. It is assumed that there is a budget for performing secondary screening on containers that yield a system alarm. This paper explores the relationships and tradeoffs between prescreening, secondary screening costs, and the efficacy of radiation detectors. The key contribution of this analysis is that it provides a risk-based framework for determining how to define a system alarm for screening cargo containers given limited screening resources. The analysis suggests that highly accurate prescreening is the most important factor for effective screening, particularly when screening tests are highly dependent, and that moderately accurate prescreening may not be an improvement over treating all cargo containers the same. Moreover, it suggests that screening tests with high true alarm rates may mitigate some of the risk associated with low prescreening intelligence.

Interdiction Models and Applications

“…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]. Atkinson et al [5] develop a model of a radiation detection system in and around a city, wherein an adversary attempts to get as close as possible to a target in a city center before detonating a nuclear weapon.…”

Sensor Management Problems of Nuclear Detection

“…The work of McLay et al [MLN09] suggests that effective prescreening, such as that based on manifest data, can be an important component of cargo screening when there are limited screening resources.…”

“…In so doing, they develop operational models and make specific recommendations on which key uncertainties are most important to resolve, how to improve the existing screening process, as well as how to most effectively utilize new technologies. McLay et al [MLN09] develop a linear programming model for screening cargo for nuclear materials at ports of entry. Their approach defines a framework for determining alarms when there are limited screening resources.…”

Network deployment of radiation detectors with physics-based detection probability calculations

“…Checkpoints with portal detectors therefore employ a two-tier screening process where the primary detector's alarm produces a secondary inspection. Our focus is on the primary detector as opposed to detailed modeling of multi-tier systems (see, e.g., Boros et al 2009;McLay et al 2008;Wein et al 2006). …”