Polonium

Polonium is a chemical element with symbol Po and atomic number 84, discovered in 1898 by Marie Curie and Pierre Curie. A rare and highly radioactive element with no stable isotopes, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Applications of polonium are few. They include heaters in space probes, antistatic devices, and sources of neutrons and alpha particles. Because of its position in the periodic table, polonium is sometimes classified as a metalloid. Other sources say that on the basis of its properties and behavior, it is "unambiguously a metal".

Characteristics

Isotopes

Polonium has 33 known isotopes, all of which are radioactive. They have atomic masses that range from 188 to 220 u. ²¹⁰Po (half-life 138.376 days) is the most widely available. The longer-lived ²⁰⁹Po (half-life 125.2 ± 3.3 years, longest-lived of all polonium isotopes) and ²⁰⁸Po (half-life 2.9 years) can be made through the alpha, proton, or deuteron bombardment of lead or bismuth in a cyclotron.

Isotopes of polonium

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.

Polonium-210

²¹⁰Po is an alpha emitter that has a half-life of 138.376 days; it decays directly to its daughter isotope 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.