Polonium-210
Polonium (Po) has 33 isotopes, all of which are radioactive, with between 186 and 227 nucleons. 210Po with a half-life of 138.376 days has the longest half-life of naturally occurring polonium. 209Po with a half-life of 125 years has the longest half-life of all isotopes of polonium. 209Po and 208Po (half-life 2.9 years) can be made through the alpha, proton, or deuteron bombardment of lead or bismuth in a cyclotron.
210Po is an alpha emitter that has a half-life of 138.376 days; it decays directly to stable 206Pb. A milligram of 210Po emits as many alpha particles per second as 5 grams of 226Ra. A few curies (1 curie equals 37 gigabecquerels) of 210Po emit a blue glow caused by excitation of surrounding air. A single gram of 210Po generates 140 watts of power. Because it emits many alpha particles, which are stopped within a very short distance in dense media and release their energy, 210Po has been used as a lightweight heat source to power thermoelectric cells in artificial satellites; for instance, a 210Po heat source was also in each of the Lunokhod rovers deployed on the surface of the Moon, to keep their internal components warm during the lunar nights. Some anti-static brushes, used for neutralizing static electricity on materials like photographic film, contain a few microcuries of 210Po as a source of charged particles.210Po is also used in initiators for atomic bombs through the (α,n) reaction with beryllium.
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