Advanced Fluoropolymer Vessels for Ultra-Clean Ionization and Scintillation Detectors

75336S A broad category of experiments in astro-particle and high energy physics requires the construction of ultra-high-purity and ultra-low-radioactive-background, cubic-meter-scale vessels to be used as containers for ionization and scintillation media. Double-beta decay experiments, solar neutrino experiments, and dark matter searches would all benefit from this technology. Plastics are among the materials with lowest radioactive contaminations, but they are usually not considered suitable because of their modest range of operating temperatures and their outgassing properties. This project will develop vessels made from high purity fluoropolymers, addressing the common problems of thermal expansion and stability at extreme temperatures, and vacuum/pressure sealing and plumbing, while maintaining ultra-low radioactivity properties. In particular, modified polytetrafluoroethylene (PTFE) sintering and sealing process methods will be developed, leading to the production a 67 liter chamber for the Enriched Xenon Observatory (EXO). In Phase I, PTFE welding techniques were developed both for sealing the chamber and for attaching plumbing and adapter fittings; a technique was developed that successfully fused the chamber material while maintaining an interior temperature low enough to avoid damaging the drift cell components installed inside; and the chamber was installed at the EXO laboratory at Stanford University. Phase II will fabricate a larger prototype chamber for the EXO Project, and also develop PTFE welding techniques for thicker container wall sections. Commercial Applications and Other Benefits as described by the awardee: The processing methods developed to fabricate the modified PTFE chamber should have application to semiconductor processing and chemical handling components, bio-reactors and other high purity bio-pharmaceutical labware, and medical devices. The ultra-low radioactive background properties may have use national security applications. The molding, sintering, and welding techniques should have uses in high purity applications that now utilize conventional compression molding processes.