page_title: Plutonium(IV) oxide
section_title: Applications
hierarchical_section_title: Plutonium(IV) oxide / Applications
caption_attribution_description: English: Plutonium-238 sphere under its own light. PU-238, with a half-life of 89 years, is being used in space applications requiring a power source with a long service life. PU-238 has a relatively high heat production rate which makes it useful as a power source. As a power and heat source, PU-238 has also been used to power instruments left on the Moon by Apollo astronauts, weather satellites and interplanetary probes. The interplanetary probe, Pioneer-10 (powered by a PU-238 source), recently left the solar system. Image ID: 2006407
context_page_description: Plutonium(IV) oxide is the chemical compound with the formula PuO₂. This high melting-point solid is a principal compound of plutonium. It can vary in color from yellow to olive green, depending on the particle size, temperature and method of production.
context_section_description: PuO₂, along with UO₂, is used in MOX fuels for nuclear reactors. Plutonium-238 dioxide is used as fuel for several deep-space spacecraft such as the 'New Horizons' Pluto probe as well as in the Curiosity rover on Mars. The isotope decays by emitting α-particles, which then generate heat (see radioisotope thermoelectric generator). There have been concerns that an accidental re-entry into Earth's atmosphere from orbit might lead to the break-up and/or burn-up of a spacecraft, resulting in the dispersal of the plutonium, either over a large tract of the planetary surface or within the upper atmosphere.  However, although at least two spacecraft carrying PuO₂ RTGs have reentered the Earth's atmosphere and burned up (Nimbus B-1 in May 1968 and the Apollo 13 Lunar Module in April 1970), the RTGs from both spacecraft survived reentry and impact intact, and no environmental contamination was noted in either instance; in any case, RTGs since the mid-1960s have been designed to remain intact in the event of reentry and impact, following the 1964 launch failure of Transit 5-BN-3 (the early-generation plutonium-metal RTG on board disintegrated upon reentry and dispersed radioactive material into the atmosphere north of Madagascar, prompting a redesign of all U.S. RTGs then in use or under development).
  Physicist Peter Zimmerman, following up a suggestion by Ted Taylor, demonstrated that a low-yield (1-kiloton) nuclear weapon could be made relatively easily from plutonium oxide.  A plutonium-oxide bomb would have a considerably larger critical mass than one made from plutonium metal (almost three times larger, even with the oxide at maximum crystal density; if the oxide were in powder form, as is often encountered, the critical mass would be much higher still), due both to the lower density of plutonium in PuO₂ compared with plutonium metal and to the added inert mass of the oxygen contained.
caption: A pellet of PuO2 glows from the decay of isotope plutonium-238 it contains
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