Bismuth (83Bi) has 41 known isotopes, ranging from 184Bi to 224Bi. Bismuth has no stable isotopes, but does have one very long-lived isotope; thus, the standard atomic weight can be given as 208.98. Although bismuth-209 is now known to be radioactive, it has classically been considered to be a stable isotope because it has a half-life of approximately 2.01×1019 years, which is more than a billion times the age of the universe. Besides 209Bi, the most stable bismuth radioisotopes are 210mBi with a half-life of 3.04 million years, 208Bi with a half-life of 368,000 years and 207Bi, with a half-life of 32.9 years, none of which occurs in nature. All other isotopes have half-lives under 1 year, most under a day. Of naturally occurring radioisotopes, the most stable is radiogenic 210Bi with a half-life of 5.012 days. 210mBi is unusual for being a nuclear isomer with a half-life multiple orders of magnitude longer than that of the ground state.

List of isotopes

Bismuth-213

Bismuth-213 (213Bi) has a half-life of 45 minutes and decays via alpha emission. Commercially, bismuth-213 can be produced by bombarding radium with bremsstrahlung photons from a linear particle accelerator, which populates its progenitor actinium-225. In 1997, an antibody conjugate with 213Bi was used to treat patients with leukemia. This isotope has also been tried in targeted alpha therapy (TAT) program to treat a variety of cancers. Bismuth-213 is also found in the decay chain of uranium-233, which is the fuel bred by thorium reactors.