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Scientists use 'trinitite' from 1945 to help decode nuclear blasts

Samples taken from the US site of the Trinity atomic bomb test allow scientists to better understand how to track the source of a detonated nuclear weapon.

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The team took a thin slice of the button-shaped trinitite sample bought from a mineral collector, polished it, and then analyzed it under an electron microscope, which can reveal tiny details within the sample. Rather than finding the uniformly mixed blob of fused New Mexico soil that many suspected, the team found layers and swirls that suggests turbulence within the molten material before it cooled. And they uncovered clear differences in the composition of the slice from one location to another across the sample.

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The team then measured x-rays coming off the still slightly radioactive material, building a kind of map they could use to compare against the locations of different compounds in the sample. Finally the scientists used two types of spectrometers to identify the different compounds and their variations, or isotopes, which allowed them to distinguish between material from the bomb and natural material that may have been swept up from the landscape as the fireball rose.

After analyzing the results, they were able to distinguish between naturally occurring uranium and the enriched uranium used in what weapons designers call a bomb's "tamper" – in this case a layer of uranium surrounding the "gadget's" plutonium core to improve the bomb's explosive efficiency.

The results represent "a big step forward," says Kim Knight, a geochemist working in the field of nuclear forensics at the Lawrence-Livermore National Laboratory in Livermore, Calif.

She notes that a great deal of emphasis has been placed on tools needed to analyze nuclear material intercepted before it can do any harm. Fahey's team's work highlights "a renewed interest in looking at relationships which may be preserved" in post-detonation debris "that we just weren't as interested in previously."

In addition, by unveiling the results in a publicly available scientific journal, in this case the Proceedings of the National Academy of Sciences, the work gives policymakers and budgeteers some sense that scientists are making progress in devising the techniques that will identify the design and sources of nuclear devices terrorists might use, she says.

The challenge, experts say, is developing the tools to analyze nuclear evidence with a high degree of confidence in the results and in a timely manner to allow policymakers to marshal a speedy response against the right perpetrators in the event of an attack.

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