Pu238

Plutonium-238 (Pu-238) is a radioactive isotope of plutonium with 94 protons and 238 nucleons. It decays via alpha emission to uranium-234, with a half-life of about 87.7 years. Pu-238 has a high specific activity, releasing heat as it decays, making it useful as a long-lived heat source.

Chemically and physically, Pu-238 is commonly handled and stored as plutonium dioxide (PuO2), a ceramic material that can withstand high temperatures and remain chemically stable over long periods. In practical applications, Pu-238 is encapsulated in robust containers and used in forms that optimize containment and heat transfer.

The primary use of Pu-238 is as a heat source in space exploration. It powers radioisotope thermoelectric generators (RTGs) and, to a lesser extent, radioisotope heater units (RHUs) that provide thermal energy or electrical power in environments where solar power is impractical. Notable missions relying on Pu-238 heat sources include various Voyager, Cassini, and Mars rover missions, as well as more recent Mars missions that employ MMRTGs for continuous operation.

Production and history have-centered Pu-238 within nuclear programs. It is produced in reactors by irradiating neptunium-237 targets, which decay to Pu-238. Production has occurred in several countries, with periods of interruption and renewed efforts to supply NASA missions. Pu-238 is tightly regulated due to its radiotoxicity and proliferation risks, with handling and transport governed by strict safety and licensing requirements.

Safety considerations emphasize that Pu-238 is an alpha emitter and radiotoxic if ingested or inhaled. External exposure is largely mitigated when encapsulated in devices, but strict containment, monitoring, and licensing are required for any handling, storage, or transport.