The Betavoltaic Conversion Ceiling: Maximum and Realistic Electrical Power per Gram for Tritium, Nickel-63, and Promethium-147

Derives the maximum electrical power per gram for tritium, nickel-63 and promethium-147 betavoltaic sources from decay energy, mean beta energy and semiconductor pair-creation energy, then applies self-absorption and radiation-damage models to obtain realistic planar power densities. Ideal beta power is 325.10 mW/g (tritium), 5.85 mW/g (Ni-63) and 340.42 mW/g (Pm-147); realistic silicon planar figures are 2.26, 0.100 and 16.68 mW/g respectively. At one-curie inventories devices deliver 0.2 to 18.0 microwatts, serving long-lived microwatt sensors and not milliwatt-to-watt loads. All numbers from the accompanying Python script. SIMULATED, NOT MEASURED.