Advanced Fluoropolymer Vessels for Ultra-Clean Ionization and Scintillation Detectors

75336-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 of ultra-clean fluoropolymers, addressing the common problems of thermal expansion and stability at extreme temperatures, electrical feed-through, and vacuum/pressure sealing and plumbing, while maintaining ultra-low radioactivity properties. Phase I will focus on developing modified polytetrafluoroethylene (PTFE) sintering and sealing process methods, needed to produce a prototype chamber with an interior volume of approximately 56 liters, such as required for the Enriched Xenon Observatory. Installation methods to feed-through instrumentation wire will be developed by analyzing a variety of wire materials and melt-processible fluoropolymers. Vacuum testing (with He and heavier gases), mechanical property analysis, and neutron activation analysis all will be used to qualify results. 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-pharmaceutical labware, and medical devices. The ultra-low radioactive background properties may be used for national security applications. The molding, sintering, and welding techniques should have uses in high purity applications that now utilize conventional compression molding processes.