J. Webster “Cost-Sensitive Classification Methods for the Detection of Smuggled Nuclear Material in Cargo Containers”, Ph.D. Dissertation, Nuclear Engineering, Texas A&M University, College Station, TX (2013).
Classification problems arise in so many different parts of life – from sorting machine parts to diagnosing a disease. Humans make these classifications utilizing vast amounts of data, filtering observations for useful information, and then making a decision based on a subjective level of cost/risk of classifying objects incorrectly. This study investigates the translation of the human decision process into a mathematical problem in the context of a border security problem: How does one find special nuclear material being smuggled inside large cargo crates while balancing the cost of invasively searching suspect containers against the risk of al lowing radioactive material to escape detection? This may be phrased as a classification problem in which one classifies cargo containers into two categories – those containing a smuggled source and those containing only innocuous cargo. This task presents numerous challenges, e.g., the stochastic nature of radiation and the low signal-to-noise ratio caused by background radiation and cargo shielding. In the course of this work, we will break the analysis of this problem into three major sections – the development of an optimal decision rule, the choice of most useful measurements or features, and the sensitivity of developed algorithms to physical variations. This will include an examination of how accounting for the cost/risk of a decision affects the formulation of our classification problem. Ultimately, a support vector machine (SVM) framework with F -score feature selection will be developed to provide nearly optimal classification given a constraint on the reliability of detection provided by our algorithm. In particular, this can decrease the fraction of false positives by an order of magnitude over current methods. The proposed method also takes into account the relationship between measurements, whereas current methods deal with detectors independently of one another.