Radiation Detection Using Passive Surface Acoustic Wave Sensors

Initial work would focus on determining which absorbents are to be evaluated (based upon the current literature and discussions with other researchers at PNNL evaluating for the medical industry's use). These would include materials such as various polymers (i.e. PDMS), graphite/graphene, metal oxides, and the use of high surface area/high porosity materials such as aerogels/xerogels. Once the initial down-select is complete, the next phase will focus on determining the most effective deposition methods for the selected absorbents. The NASA Chemical Analysis Branch and the Applied Chemistry Laboratory have a variety of instrumentation that is applicable to this type of work, including a Chemat Technology Spin Coater for the deposition of thin films (polymer, metal-oxide, and metal organic) using a variety of vacuum chucks, a custom-built Photo Vapor Deposition (PVD) magnetron sputtering system for the evaporative coating of thin metal films, as well as a Denton Vacuum Desk IV Sputter Coater for the deposition of metal and carbon coatings. Local radiation sources would then be utilized to attempt to demonstrate a measurable mass loss on the produced coatings, which could be projected to produce a response in a PSAW sensor system. Pegasense, our commercial partner and IP inventor will work with the University of Central Florida and its medical college to identify local radiation sources in addition to known NASA sources/opportunities. Additionally, testing could be coupled/coordinated with ongoing evaluation of avionics equipment in Massachusetts General Hospital's Proton Beam or with Brookhaven National Labs.

The goal of this project is to combine the advantageous qualities of the PSAWs with a surface coating capable of detecting the presence of various forms of ionizing radiation. Due to the small size and power requirements, these could be deployed in a manner similar to conventional dosimeter style badges, but with the ability for a real-time or near real-time reading through the use of wireless communications. If successful, the user would gain the benefits of both conventional monitoring techniques (area and passive personnel monitoring) while also gaining the capability to distinguish between different forms of ionizing radiation. The detection of radiological species (i.e., ionizing radiation) by PSAWs is more challenging than for conventional chemical species, as gamma and beta particles exhibit no observable mass. Therefore, traditional chemical coatings capable of sorbing these particles are ineffective, as they will not reflect a mass change upon exposure. However, due to the highly energetic nature of these ionizing particles it is possible to select a coating which will be degraded via radiolysis upon exposure to certain types of radiation and exhibit a detectable mass loss. For example, studies have shown many polymers (such as polyethylene, PTFE, EDPM) will exhibit degradation upon exposure to tritium through the evolution and loss of hydrogen gas through a beta decay process (Clark 2013). Detection of tritium is normally a difficult process due to the low energy of the accompanying radiation; however, the minute changes in mass associated with certain polymers exposed to tritium and the sensitivity of PSAW sensor should make it possible to detect. Similarly, exposure of certain polyethers (polyethylene, polypropylene, polyvinylchloride) to gamma radiation has also been shown to cause oxidative degradation and the evolution of gas byproducts, leading to a mass loss for the chemically selective coating which can be detected by a perturbation in the frequency of the surface acoustic wave (Aymes-Chodur et al, 2011). Another possible method for the detection of ionizing radiation is the use of a trapping polymer film to capture alpha particles, which unlike beta and gamma particles due have an observable mass that can be detected in the traditional manner of a PSAW. Experimental results have shown that certain epoxy/polyvinyl acetate foams can be used to capture these particles, as well as other radioactive molecules such as radon.

This is early/mid-stage (TRL 2) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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