section_path: Characteristics/Isotopes
section_name: Isotopes
paragraph_text: Isotopes
  
  Gold has only one stable isotope, Au, which is also its only naturally occurring isotope, so gold is both a mononuclidic and monoisotopic element. Thirty-six radioisotopes have been synthesized, ranging in atomic mass from 169 to 205. The most stable of these is Au with a half-life of 186.1 days. The least stable is Au, which decays by proton emission with a half-life of 30 μs. Most of gold's radioisotopes with atomic masses below 197 decay by some combination of proton emission, α decay, and β decay. The exceptions are Au, which decays by electron capture, and Au, which decays most often by electron capture (93%) with a minor β decay path (7%). All of gold's radioisotopes with atomic masses above 197 decay by β decay.
  
  At least 32 nuclear isomers have also been characterized, ranging in atomic mass from 170 to 200. Within that range, only Au, Au, Au, Au, and Au do not have isomers. Gold's most stable isomer is Au with a half-life of 2.27 days. Gold's least stable isomer is Au with a half-life of only 7 ns. Au has three decay paths: β decay, isomeric transition, and alpha decay. No other isomer or isotope of gold has three decay paths.