AstroPower proposes to develop gallium phosphide energy converters optimized for radio luminescent light based power supplies. A "two-step" or "indirect" process is used where a phosphor is excited by radioactive decay products to produce light that is then converted to electricity by a GaP energy converter. This "indirect" energy conversion of B-radiation to electrical energy can be realized by applying recent developments in tritium based radio luminescent (RL) light sources in combination with the high cell operating voltage than can be achieved under low illumination with gallium phosphide photodiodes. This proposal addresses the development of semiconductor power converters that are suitable for low activity radioisotope fuels such as tritium (T2). Tritium has been neglected in semiconductor conversion due to its low average energy emission, 5.7 keV, but recent materials advances have advances have made tritium sources practical sources practical. Tritium has a relatively long half life, a safe decay product, is easily shielded, and is required in only small amounts for milliwatt power supplies.
