Bismuth-209
Bismuth-209 is an isotope of bismuth with the longest known half-life of any nuclide that undergoes α-decay ; the decay product is thallium-205. It has 83 protons and a magic number of 126 neutrons, and naturally-occurring bismuth consists entirely of this isotope.
Decay properties
Bismuth-209 was long thought to have the heaviest stable nucleus of any element, but in 2003, a research team at the in Orsay, France, discovered that Bi undergoes alpha decay with a half-life now given more precisely as years, over 10 times longer than the estimated age of the universe. The heaviest nucleus considered to be stable is now lead-208 and the heaviest stable monoisotopic element is gold.Theory had previously predicted a half-life of 4.6 years. It had been suspected to be radioactive for a long time. The decay produces a 3.14 MeV alpha particle plus thallium-205.
[Image:Decay Chain(4n+1, Neptunium Series).svg|200px|thumb|right|Bismuth-209 occurs in the neptunium series decay chain.]
Due to its extremely long half-life, Bi can be treated as non-radioactive for nearly all applications. It is much less radioactive than human flesh, so it poses no real radiation hazard. Though Bi holds the half-life record for alpha decay, it does not have the longest known half-life of any nuclide; this distinction belongs to tellurium-128 with a half-life estimated at years by double beta decay.
The half-life of Bi was confirmed in 2012 by an Italian team in Gran Sasso who reported years. They also reported an even longer partial half-life for alpha decay of Bi to the first excited state of Tl, estimated at 1.66 years. Even though this value is shorter than the half-life of Te, both alpha decays of Bi hold the record of the thinnest natural line widths of any measurable physical excitation, estimated respectively at ΔΕ ≈ and ΔΕ ≈ in application of the uncertainty principle.
Applications
Because all primordial bismuth is bismuth-209, bismuth-209 is used for all normal applications of bismuth, such as being used as a replacement for lead, in cosmetics, in paints, and in several medicines such as Pepto-Bismol. Alloys containing bismuth-209 such as bismuth bronze have been used for thousands of years.Synthesis of other elements
Po can be manufactured by bombarding Bi with neutrons in a nuclear reactor and around 100 grams of Po are produced each year. Po and Po can be made through the proton bombardment of Bi in a cyclotron. Astatine can also be produced by bombarding Bi with alpha particles. Traces of Bi have also been used to create gold in nuclear reactors.Bi has been used as a target for the creation of several isotopes of superheavy elements such as dubnium, bohrium, meitnerium, roentgenium, and nihonium.