Radionuclide production for radioisotope micro-power source technologies
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Radioisotope micro-power sources (RIMS) hold great promise for the development of small power sources for use in numerous applications, including micro electromechanical (MEMS) systems, due to the five orders of magnitude difference in the specific energy density available in radioactive decay versus chemical reactions. While a number of conversion schemes can be employed in RIMS, direct voltaic conversion technologies are compatible with the semiconductor manufacturing processes used in MEMS. A direct conversion solid-state betavoltaic RIMS device consists of a p-n semiconductor coupled with a beta-emitting radionuclide. Liquid semiconductor betavoltaic devices were investigated simultaneously with the solid-state designs as an alternative concept designed to minimize radiation induced lattice damage that occurs in solid-state devices formed through interaction with high-energy charged particles. A liquid semiconductor RIMS device operates similarly to a solid-state semiconductor; however, the device uses Schottky and ohmic contacts that encapsulate a radionuclide in its liquid state. Radioisotopes used for the fabrication of solidstate semiconductor sources include ₃₃P and ₁₄₇Pm. Sulfur-35 was selected as the isotope for liquid semiconductor tests because it can be produced in high specific activity and it is chemically compatible with the liquid semiconductor media under investigation. The irradiation, separation and subsequent chemistries of curie amounts of activity were performed at the University of Missouri Research Reactor (MURR) for ₃₅S and ₁₄₇Pm.