Tritiation and Stability Measurements of Nitroxide for Betavoltaic Cells

Abstract : Beta radioisotope energy sources, such as tritium (3H), have shown significant potential in satisfying the needs of an energy-driven world. The drawbacks of current beta source compounds include low beta-flux power, intrinsic isotope leakage, and beta self-absorption. The figure of merit for a tritiated compound is the input power or specific surface activity of the thin layer (Ci/cm2) where an optimal portion of incident beta particles are penetrating the semiconductor depletion region. The goal is to synthesize a compound with an effective surface activity (from one side) of 30 mCi/cm2 where it can be used for both planar and high aspect ratio, textured structures (pillared, etched, etc.). Nitroxides are chosen to meet these requirements because of physical properties (solid and pliable at standard temperature and pressure and controllable deuteration and hydrogenation synthesis from previous published work). Calculations show that only 1 of the 4 compounds can possibly meet short-term goal of approximately 30 mCi/cm2, but its tritiation stability during and after synthesis is unknown. As a proof of concept with respect to tritiation, the nitroxide 4-methoxycarbonyl-methylene-2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) is tritiated (3H) with a specific activity of 103 Ci/g. The stability of TEMPO containing tritium in a solution of toluene is achieved. TEMPO in toluene is found to be 100 stable at least up to 27 days, when the experiments are terminated, as no loss of tritium from a solution of this nitroxide is observed.