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

Atmospheric monitoring of radioactive Xenon with high sensitivity is critical for the global verification of the Comprehensive Nuclear Test Ban Treaty. Typically, a betagamma coincidence detector is used for the radio Xe monitoring, where plastic scintillators and inorganic scintillators are used simultaneously for the detection of the beta particles and gamma photons, respectively. One of the unique challenges with the use of beta cells is the permeation and entrapment of Xe gas into the porous plastic scintillator. The result is an undesired residual activity from radioXe in the detector that affects all the subsequent measurements, leading to an elevated system detection limit, referred to as the “Memory Effect”. The low Xe activity expected to reach a monitoring system from a nuclear explosion, in combination with the relatively high Xe background from nuclear plants and medical isotope facilities, makes the memory effect a critical issue to be addressed. RMD proposes to address this challenge by applying very thin conformal layer of gasdiffusionbarrier coatings on the beta cell surface to prevent the Xe permeation, without affecting the energy resolution of the detector. During the Phase I program, RMD demonstrated the feasibility of applying very thin layer of aluminum oxide coatings by atomic layer deposition on the plastic scintillator surface to prevent the Xe permeation. The coatings were applied at low temperatures to prevent damage to the plastic scintillators. These coatings exhibit up to 99% reduction in memory effect. During the Phase II, RMD designed and built a custommade coating system capable of batch processing the beta cells. Currently work is underway at PNNL for the evaluation of ALDcoated beta cell for memory effects. While we are confident that our ALD optimization for lowtemperature coatings on beta cells will be successful before the end of Phase II, crucial work remains to be accomplished to translate the technology into commercial production. During Phase IIB, RMD will develop the commercialreadiness and the manufacturing reliability for the coating processing of the beta cells to be used in Xenon Monitoring Systems and establishing RMD as a future player for the more ambitious betagamma coincidence detector manufacturing. 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 lowtemperature non permeable protective barriers 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.