Investigating rapid alpha-decay induced aging of 238PuO2 by Raman Spectroscopy

Abstract

Investigating alpha-decay induced aging in PuO₂ is useful in nuclear forensics; helping to determine the time since last calcination. This was previously investigate by monitoring the damage to ²⁴⁰PuO₂ over the course of a few years. The rate of alpha-decay induced aging has long been assumed to scale only with the decay rate of other isotopes without direct verification. This article reports the first alpha-decay aging study of ²³⁸PuO₂ by Raman spectroscopy. Contrary to the expected 10 days for ²³⁸PuO₂ to reach steady state based on ²⁴⁰PuO₂ studies, the alpha aging curve reached an approximate steady state ∼24–30 h after laser annealing. While the cause of the order of magnitude decrease is unknown, it is speculated that dynamic annealing could contribute to the differences in rate of induced aging. The Raman spectra of annealed and aged ²³⁸PuO₂ matched the expected features in ²³⁹PuO₂ and ²⁴⁰PuO₂ spectra; showing no formation of new stable chemical species in the material such as secondary Pu oxide phases (e.g., Pu₄O₉). Results indicate that ²³⁸Pu could be leveraged for rapid alpha-decay aging studies to characterize alpha-decay induced features and better understand matrix temperatures and the annealing of Frankel pair defects.