  Every country that has made nuclear weapons has used uranium enrichment.
Despite the centrality of this technology to international security, there is
still no reliable physical marker of past enrichment that can be used to
perform forensic verification of historically produced weapons. We show that
the extremely low radioactivity from uranium alpha emissions during enrichment
leaves detectable and irreversible calorimetric signatures in the common
enrichment gasket material PTFE, allowing for historical reconstruction of past
enrichment activities at a sensitivity better than one weapon's quantity of
highly enriched uranium. Fast scanning calorimetry also enables the measurement
of recrystallization enthalpies of sequentially microtomed slices, confirming
the magnitude and the type of radiation exposure while also providing a
detection of tampering and a method for analyzing field samples useful for
treaty verification. This work opens the door for common items to be turned
into precise dosimeters to detect the past presence of radioactivity, nuclear
materials, and related activities with high confidence.
