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Whether it’s a nuclear weapon, a radiological dispersion device (RDD or dirty bomb) or a radiation exposure device (RED), they all involve radioactive materials that emit radiation at some point in their life history. It’s this radiation, or the radiological material itself, that can be detected and/or fingerprinted to determine where it came from.
This can occur before the device is used. Or after. Obviously, we want to detect it beforehand.
We had been quietly coordinating with other global agencies for decades to detect and stop nuclear trafficking, but the attacks of September 11, 2001 changed things quite a bit. The creation of the Department of Homeland Security (DHS) in 2002, and its Domestic Nuclear Detection Office (DNDO) in 2005, put the issue front and center.
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The Nuclear Forensics International Technical Working Group (ITWG) was founded around the time that nuclear smuggling was increasing at borders across Northern Europe, raising concerns about nuclear proliferation. From 1993 to 2001, there were over 500 confirmed incidences with special nuclear materials and other radioactive sources (see figure).
Radioactive materials naturally decay along well-known pathways, but they can be very complicated. Similarly, if you split some atoms, like uranium-235 (235U) or plutonium-239 (239Pu), in either a reactor or a bomb, the pieces that form are also well-known. This very complexity makes it possible to trace where certain radioactive materials came from or how certain radioactive materials were formed.
We can even determine when some of them were formed, called radiochronometry, using the differences in decay rates of various elements and the rate of in-growth of their decay products, or daughters.
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Global fallout is dominated by 1950s and 1960s above ground atmospheric tests of high-yield fusion bombs which produce higher amounts of fission products (137Cs and 90Sr) and lower amounts of 239Pu than lower-yield fission bombs (like North Korea’s) which produce lower amounts of fission products and lower amounts of 240Pu and 242Pu.
Different production runs for weapons grade material will produce different ratios, i.e., Savannah River-produced Pu will have a higher Pu240/Pu239 ratio than that produced at the Hanford Site in Washington State. So weapons will have a unique signature depending upon where their materials were made.
For nuclear power plants, the isotopes produced depend upon the fuel used and the burn-up rates for that plant.
Uranium Enrichment facilities will have a simple U signature, either enriched or depleted in 235U.
Nuclear waste repositories will reflect whatever is being disposed or stored there. A spent fuel waste site, as Yucca Mountain was meant to be, would have a signature similar to a power plant but have more non-volatiles. America’s weapons waste repository, WIPP, has more weapons-grade isotopes such as 239Pu, plus lots of U and even other metals, such as Be, that are used in weapons but not in power plants.
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In Ulm, Germany, over 200 pellets of a radioactive substance were discovered in a bank safe by the police in 1996. The shape suggested that they were nuclear fuel from a light water reactor. Laboratory testing showed that the substance was 4.8% 235U. Two nuclear power plants were known to use these types of pellets, and the microscopic texture of the fuel’s surface correctly identified which plant they came from.
In 1961, we performed an underground atomic bomb test in southeastern New Mexico, called Project Gnome. If you collect soil in the region, and perform some nuclear forensics, like we did at the NMSU CEMRC laboratories in Carlsbad, NM you can map the region impacted by the test as it fades away into the global background using the ratios among 239Pu, 240Pu and 241Am.
Read more at CSI: Nuclear
