section_path: Characteristics/Isotopes
section_name: Isotopes
paragraph_text: Isotopes
  
  There are 29 isotopes of copper. Cu and Cu are stable, with Cu comprising approximately 69% of naturally occurring copper; both have a spin of 3 ⁄ 2. The other isotopes are radioactive, with the most stable being Cu with a half-life of 61.83 hours. Seven metastable isomers have been characterized; Cu is the longest-lived with a half-life of 3.8 minutes. Isotopes with a mass number above 64 decay by β, whereas those with a mass number below 64 decay by β. Cu, which has a half-life of 12.7 hours, decays both ways.
  
  Cu and Cu have significant applications. Cu is used in Cu Cu-PTSM as a radioactive tracer for positron emission tomography.