Plutonium238

Plutonium-238 (Pu-238) is a radioactive isotope of plutonium used mainly as a heat source in radioisotope thermoelectric generators (RTGs) for spacecraft. It is produced artificially in nuclear reactors and does not occur naturally in any significant amount.

Pu-238 has an atomic number of 94 and a mass number of 238. It decays by alpha emission to uranium-234 and has a half-life of 87.7 years. The decay releases considerable heat, about 0.56 watts per gram at room temperature, which RTGs convert into electricity over many years. External radiation from Pu-238 is dominated by alpha particles, which have limited penetration; however, internal exposure from inhalation or ingestion is highly hazardous. Pu-238 is typically handled as a ceramic oxide, PuO2, for stability and reliability in long-term use.

Production of Pu-238 is accomplished in nuclear reactors. Neptunium-237 is irradiated to form neptunium-238, which beta-decays to Pu-238. The isotope is then chemically separated and fabricated into fuel forms for RTGs. Production has traditionally been limited and subject to supply constraints, which has influenced planning for space missions.

Applications and history: Pu-238 is valued for its steady heat output, enabling long-duration spacecraft power systems in environments where solar energy is unavailable or impractical. Notable missions using Pu-238 RTGs include Voyager, Galileo, Cassini–Huygens, New Horizons, and Curiosity on Mars, among others. The material is strictly regulated due to radiotoxicity and proliferation concerns, with careful controls on production, transport, and use.

Safety and regulation: Pu-238 requires stringent safety measures to prevent inhalation or ingestion. Shielding, containment, and regulatory oversight govern its handling, storage, and disposal.