 It is also used as a thermal power source in radioisotope thermoelectric generator power packs.These use heat produced by radioactive decay of strontium-90 to generate heat, which can be converted to electricity using a thermocouple.Strontium-90 has a shorter half-life, produces less power, and requires more shielding than Plutonium-238, but is cheaper as it is a fission product and is present in a high concentration in nuclear waste and can be relatively easily chemically extracted.