Polonium (pronounced
/p?'lo?ni?m/,
po-LOH-nee-?m) is a
chemical element with the symbol
Po and
atomic number 84, discovered in 1898 by
Marie and
Pierre Curie. A rare and highly
radioactive metalloid,
[1] polonium is chemically similar to
bismuth[2] and
tellurium, and it occurs in
uranium ores. Polonium has been studied for possible use in heating
spacecraft. It is unstable; all
isotopes of polonium are radioactive. Polonium is very volatile; it will almost completely vaporize at room temperatures.
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. 209Po (half-life 103 years) and 208Po (half-life 2.9 years) can be made through the alpha, proton, or deuteron bombardment of lead or bismuth in a cyclotron.
The majority of the time 210Po decays by emission of an alpha particle only, not by emission of an alpha particle and a gamma ray. About one in 100,000 alpha emissions causes an excitation in the nucleus which then results in the emission of a gamma ray.[6] This low gamma ray production rate (and the short range of alpha particles) makes it difficult to find and identify this isotope. Rather than gamma ray spectroscopy, alpha spectroscopy is the best method of measuring this isotope.
Polonium is a radioactive element that exists in two metallic allotropes. The alpha form has a simple cubic crystal structure with an edge length of 335.2 picometres; the beta form is rhombohedral.[7] [8] The structure of polonium has been characterized by X-ray diffraction [9][10] and electron diffraction.[11]
