Isotopes of bismuth

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 208.98040(1). 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.