The hyperfine structure of rubidium energy levels, are used as resonances in some types of atomic clocks: Rubidium Atomic Clock With Fluorescence Optical Pumping And Method Using Same (1997).
Rubidium is also used as an ingredient in special types of glass: Lithium Silicate Glass Ceramic And Glass With Rubidium Oxide Content (2016).
Rubidium 82 is used for positron emission tomography.
Rubidium is very similar to potassium and tissue with high potassium content will also accumulate the radioactive rubidium. One of the main uses is myocardial perfusion imaging. Rubidium collects more in brain tumours than normal brain tissue, allowing the use of Rb 82 radioisotope imaging to locate brain tumours: A Rubidium Generator For Cardiac Perfusion Imaging And Method Of Making And Maintaining Same (2007).
Rubidium-82 has a very short half-life of 76 seconds, and the production from decay of strontium 82 must be done close to the patient: Integrated Strontium-Rubidium Radioisotope Infusion Systems (2019).
Rubidium chloride may have applications in the management of psychological issues like mood swings and manic episodes: Use Of Rubidium And In Particular Rubidium Chloride As An Antimanic Agent And Stabilizer For Mood Swings (2000).
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All patent information has been obtained from Espacenet (European Patent Office).