Nuclear forensics – the field in which I work at the Lawrence Livermore National Laboratory, USA – uses a variety of analytical techniques and data analytics to characterize nuclear (radioactive) materials and provide as much conventional forensic information as possible. The goals generally come down to answering four simple questions about the sample: What is it? Where did it come from? How did it get there? And who was involved?
Over the years, the need for nuclear materials has increased and how those materials are produced and used is of great interest. In addition to national security in the areas of non-proliferation and arms control, there is concern about making sure nuclear materials don’t end up in the wrong hands through nuclear smuggling. Interception of smuggled nuclear materials is one area of application and requires sophisticated analytical techniques, especially if there are attempts to obfuscate how or when the material was produced. For example, based on isotope ratio measurements, the age of the production of the nuclear material can be determined, but if a smuggler wanted to try to hide the actual production age, they might blend in some of the daughter isotopes. This can typically be detected with high-precision measurements and there will be another decay sequence from the added material that can be identified.
Prior to receiving the sample, we have some information about it from the sponsor, so we bring together the team based on what we know and the sponsor’s requests. When we receive the sample, it’s logged in and photographed, evaluated for radiation levels, then we start with non-destructive testing. A typical team will include radiochemists, spectroscopists, chromatographers for GC or LC -MS, and microscopists.
I’m not sure there’s a “typical” case in nuclear forensics, but here’s one example: I was once involved in an attempted smuggling case where the person who was apprehended was supposedly transporting some uranium ores as a sample to a potential buyer. He had hidden the ores under the inserts of his shoes in his suitcase. In this case, we were able to quickly evaluate the materials using spectroscopic analysis and gamma spectroscopy to determine that these weren’t, in fact, uranium ores. There are a few other examples in the book “Nuclear Forensics Analysis,” by my colleagues Pat Grant, Ian Hutcheon, and Ken Moody.
There are some challenges – and risks – when working in this field. In particular, samples with high levels of radioactivity present handling issues and can make some analyses challenging to avoid contamination or exposure. Easily dispersed powder materials are the major concern. Fortunately, we have experience in making sure these are contained and we don’t contaminate our work areas or our equipment. We are very careful about working in a fume hood with secondary containment and monitoring our work areas for radiation.
In terms of the techniques used, spectroscopic analysis has several benefits for nuclear forensics. In particular, it can be non-destructive and non-contact, the analysis can be fast, and provides some spatial information. Of course, we use gamma spectroscopy to identify and quantify the radioactive species, although sometimes samples need to counted for extended periods of time. For optical spectroscopy, we rely on NIR diffuse reflectance, FTIR in reflectance or with ATR, and Raman – and these are usually some of the first analysis performed. These can provide some initial information about the sample that we can include in the first 24 hour report.
For example, we once had a sample of highly enriched uranium (HEU) that was a black powder and had to be handled carefully and in a hood. We were able to measure the NIR diffuse reflectance spectra with a fiber optic probe and, when compared to our database, determined it was a mixture of U3O8 and UO3 * xH2O. Knowing which form of uranium is present provides some insight about how the material was processed.
Of course, we’re always looking for new and emerging techniques that can help speed up or improve the analysis. As handheld instruments improve, they can provide some nice screening information, however, they won’t be able to replace the accuracy of the lab techniques.
Overall, working on forensic samples is always fun and exciting. At the Forensic Science Center at LLNL, we receive samples from various different agencies and no two samples are ever the same, and the challenges are always unique.
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