Polonium-209

Main isotopes of polonium

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct 208Po syn 2.898 y α 204Pb β+ 208Bi 209Po syn (125.2±3.3) y α 205Pb β+ 209Bi 210Po trace 138.376 d α 206Pb

Polonium (₈₄Po) 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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