international nuclear forensics capability would also be important as part of the International Atomic Energy Agency (IAEA) verification toolkit, particularly linked to increased access provided by the Additional Protocol. Not all countries have signed the Additional Protocol, so such sampling may be limited. However, under the Treaty on the Non-Proliferation of Nuclear Weapons,²⁶⁴ Special Inspections allow for sampling as well, although this type of inspection is not often used.

A recent study has found that, although international progress has been made in securing weapons-usable highly enriched uranium (HEU) and plutonium (Pu), the effort is still insufficient.²⁶⁵ It found that nuclear material, located in 40 countries, could be obtained by terrorists and criminals and used for a crude nuclear weapon. Through 2006, the IAEA Illicit Trafficking Database (ITDB) had recorded a total of 607 confirmed events involving illegal possession, theft, or loss of nuclear and other radioactive materials.²⁶⁶ Incidents confirmed to the ITBD involving weapons-useable material total over 8.3 kg of HEU and 370 g of Pu. Although it is difficult to predict the future course of such illicit trafficking, increasingly such activities are viewed as significant threats that merit the development of special capabilities. As early as April 1996, nuclear forensics was recognized at the G8 Summit in Moscow as an important element for monitoring and deterring illicit nuclear trafficking. Given international events over the past several years, the value and need for nuclear forensics seems greater than ever.

Determining how and where legitimate control of nuclear material was lost and tracing the route of the material from diversion through interdiction are important goals for nuclear forensics and attribution. It is equally important to determine whether additional devices or materials that pose a threat to public safety are also available. Finding the answer to these questions depends on determining the source of the material and its method of production. Nuclear forensics analysis and interpretation provide essential insights into methods of production and sources of illicit radioactive materials. However, they are most powerful when combined with other sources of information, including intelligence and traditional detective work. The certainty of detection and punishment for those who remove nuclear materials from legitimate control provides the ultimate deterrent for such diversion and, ultimately, for the intended goal of such diversion, including nuclear terrorism or proliferation. Consequently, nuclear forensics is an integral part of “nuclear deterrence” in the 21^st century.

Nuclear forensics will always be limited by the diagnostic information inherent in the interdicted material. Important markers for traditional forensics (fingerprints, stray material, etc.) can be eliminated or obscured, but many nuclear materials have inherent isotopic or chemical characteristics that serve as unequivocal markers of specific sources, production processes, or transit routes. The information needed for nuclear forensics goes beyond that collected for most commercial and international verification activities. Fortunately, the international nuclear engineering enterprise has a restricted number of conspicuous process steps that makes the interpretation process easier. Ultimately, though, it will always be difficult to