Commercial ALD Process for Elimination of Memory Effects in Xe Beta Cells

There is a need to improve the monitoring techniques for radioactive xenon (Xe) in the atmosphere, so that clandestine nuclear test explosions can be confirmed.Such monitoring is critical for verification of the Comprehensive Nuclear-Test-Ban Treaty.The plastic scintillator used for detecting radio-xenon using betagamma coincidence traps the gas in the body of the scintillator.The result is a residual Xe activity in the detector that affects subsequent measurements, leading to an elevated system detection limit, referred to as the “Memory Effect”.RMD proposes to address this challenge by conformal coating of the plastic scintillator with a material with robust gas diffusion barrier property in order to prevent the permeation of radio-xenon into the plastic scintillator.During Phase I, RMD was able to demonstrate a reduction of memory effect by more than 99% by applying a conformal coat of Al2O3 on planar plastic scintillator substrates.Special emphasis was paid to improve the near-surface chemistry that enhanced the thin film nucleation such that the thin film deposition could be processed at a low temperature of 65 C, below the softening point of the plastic scintillator.During Phase II effort, RMD will design and construct a thin film deposition tool for conformal coating of actual beta cells used in beta-gamma coincidence measurements.RMD will deposit the Al2O3 films at a low temperature of 65 C and demonstrate the elimination of the memory effect while improving the overall energy resolution of the detector.RMD will develop a commercial process for coating the beta cells required for the nuclear explosion monitoring systems.Besides the beta cell coatings, the coating technology we propose has numerous applications which include passivation of night vision systems, protective coatings on moisture sensitive materials such as the advanced scintillators, coatings for photovoltaic industry, and those for the display technologies.The low temperature non-permiable membrains are required for numerous applications with a rather large market potential.Substantial fraction of this market represents areas where the proposed technology will have an immediate impact.