Isotopes of rubidium

Isotopes of rubidium (37Rb)
Main isotopes Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
82Rb synth 1.2575 m β+ 82Kr
83Rb synth 86.2 d ε 83Kr
84Rb synth 32.82 d β+ 84Kr
β− 84Sr
85Rb 72.2% stable
86Rb synth 18.645 d β− 86Sr
ε 86Kr
87Rb 27.8% 4.97×1010 y β− 87Sr
Standard atomic weight Ar°(Rb)
  • 85.4678±0.0003
  • 85.468±0.001 (abridged)

Rubidium (37Rb) has 35 known isotopes, from 72Rb to 106Rb, with naturally occurring rubidium composed of two: stable 85Rb (72.2%) and radioactive 87Rb (27.8%). The primordial radionuclide 87Rb has a half-life of 4.97×1010 years, beta decaying to stable 87Sr. It is, as the element is, widespread on Earth as rubidium readily substitutes for potassium in all minerals. The decay of 87Rb has been used extensively in dating rocks; see rubidium–strontium dating for a more detailed discussion.

Other than 87Rb, the longest-lived radioisotopes are 83Rb with a half-life of 86.2 days, 84Rb with a half-life of 32.82 days, and 86Rb with a half-life of 18.645 days. All other radioisotopes have half-lives less than a day, most less than 20 minutes. Of the isomeric states the most stable is 82mRb at 6.472 hours.

The ground state of 82Rb has a much shorter half-life of 1.2575 minutes. It is used medically in some cardiac positron emission tomography scans to assess myocardial perfusion. It is synthesized through the longer-lived 82Sr, made in a cyclotron, though a generator. It may be administered as the chloride.

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