Isotopes of rubidium

Rubidium (₃₇Rb) has 35 known isotopes, from Rb to Rb, with naturally occurring rubidium composed of two: stable Rb (72.2%) and radioactive Rb (27.8%). The primordial radionuclide Rb has a half-life of 4.97×10 years, beta decaying to stable Sr. It is, as the element is, widespread on Earth as rubidium readily substitutes for potassium in all minerals. The decay of Rb has been used extensively in dating rocks; see rubidium–strontium dating for a more detailed discussion.

Other than Rb, the longest-lived radioisotopes are Rb with a half-life of 86.2 days, Rb with a half-life of 32.82 days, and Rb 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 Rb at 6.472 hours.

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