Investigation of CR-39 damaging mechanisms in electrochemical environments

Abstract

<p>Poly(allyl diglycol carbonate), CR-39, is a common type of plastic used in detecting and measuring radiation exposure. Incident particles damage the polymer, leaving behind latent tracks. During chemical etching, these tracks are then preferentially etched, resulting in microscale tracks where the particles have passed. In electrochemical cells, pits in CR-39 detectors have been used as evidence for presence of nuclear reactions during palladium–deuterium co-deposition. This research focuses on replicating these measurements and investigating parameters affecting pit formation. With appropriate cell designs, pits can be produced without palladium and/or deuterium in the system. Free radical formation and cavitation are proposed as alternative CR-39 damaging mechanisms. CR-39 response to ultrasound cavitation indicates cavitation as the predominant source of the initial damage on CR-39 surfaces. Pits produced during metal-hydride/deuteride co-deposition and subsequent hydrogen evolution reaction (HER) processes after etching had their diameters distributed into two partially overlapping normal distributions. Comparisons with literature suggested this diametral distribution bifurcation could be the result of cavitation collapse of two types of evolved gas nanobubbles. Spherical nanobubbles and high contact angle surface nanobubbles produce jets during their collapse, creating seed damages relative to their projection, with the spherical bubble collapse producing deeper impressions. Surface damage differences on CR-39 surface are then magnified during the etching process resulting in the observed diametral distributions. The results of this study indicate that work involving CR-39 detectors in systems with gas evolution should take cavitation effects into account, as polymer-damaging cavitation events occur during electrolysis. They also underline that CR-39 detectors can serve as a tool to characterize degradation caused by cavitation in electrolyzers.<br></p>