Plutonium

²³⁸Pu (with a half-life of 87.7 years) is used in radiothermal generators as a heat source to produce electricity. These radiothermal generators are used to power unmanned spacecraft and interplanetary probes that venture too far from the Sun to use solar power, such as the Cassini Orbiter, the Galileo spacecraft, and the Huygens and Galileo probes [75], [606], [607], [608]. ²³⁸Pu has been used in the Apollo lunar missions as part of a nuclear battery. The SNAP-27 (systems nuclear auxiliary power) system produced approximately 75 W of electrical power at 30 VDC per unit (Fig. IUPAC.94.1). The energy source was a 2.5-kg rod of ²³⁸Pu providing thermal power of approximately 1250 W [609]. ²³⁸Pu is used in pacemakers (Fig. IUPAC.94.2). ²³⁹Pu (with a half-life of 2.41×10⁴ years) is used in nuclear weapons. ²³⁹Pu is easily made in nuclear reactors by bombarding ²³⁸U with neutronsvia the reaction ²³⁸U (n, γ) ²³⁹U and ²³⁹U→ ²³⁹Pu+β −. The ²³⁹Pu made by this reaction can itself be split by neutrons to release energy and is used for energy generation in nuclear reactors [75], [610], [611].