Muon tomography attracts researchers

The latest available figures from the International Atomic Energy Agency's Illicit Trafficking Database (ITDB) show that, between January 1993 and December 2011, a total of 2,164 confirmed incidents were reported. Of these incidents, 16 involved the "unauthorised possession of high enriched uranium or plutonium" - the materials necessary to produce full nuclear weapons. A small number of the 16 "involved seizures of kilogram quantities of potentially weapons-usable nuclear material", according to the ITDB.

Black-market trading in weapons-usable materials is worrying enough, but lower-grade radiological materials also pose a threat as these may be dispersed via an explosive device or environmental contamination. While not as destructive as a fission weapon, the contamination of large areas with hazardous material may prompt widespread panic and fear, and overwhelm the state's ability to respond.

To combat this, the United States remains the largest driver of global non-proliferation efforts, with President Barack Obama committing his administration not only to safeguarding vulnerable nuclear material at their source, but also to "build on our efforts to break up black markets, detect and intercept materials in transit, and use financial tools to disrupt this dangerous trade".

One of the most prominent initiatives has been the Second Line of Defense (SLD) programme, run by the US Department of Energy's National Nuclear Security Administration (NNSA). The SLD Core programme works with foreign partners to install radiation-detection equipment at key transit points such as borders, airports, and strategic ports.