Iridium radioisotopes are used in some radioisotope thermoelectric generators. The isotope germanium-76 is a primordial radioisotope. Tritium is a radioisotope of concern in nuclear reactor waste streams. Nuclear decay processes are used in niche applications such as radioisotope thermoelectric generators. A radioisotope of iridium, , is dangerous, like other radioactive isotopes. Another use is as a carrier of strontium-90 radioisotope in radioisotope thermoelectric generators. It is also used as a thermal power source in radioisotope thermoelectric generator power packs. In 1938, John Livingood and Glenn T. Seaborg discovered the radioisotope cobalt-60. The radioisotope thermoelectric generator was also appropriately used for heat. Sr has been used as a power source for radioisotope thermoelectric generators (RTGs). Electrical power is supplied by three MHW-RTG radioisotope thermoelectric generators (RTGs). The first use of radioluminescence was in luminous paint containing radium, a natural radioisotope. It is the second longest-lived radioisotope of iodine, after iodine-129. The most stable chlorine radioisotope is Cl. RTGs convert the heat from the natural decay of a radioisotope into electricity.