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Radionuclide Basics: Radium | US EPA
Radium (chemical symbol Ra) is a naturally occurring radioactive element. The most common isotopes of radium are radium-226 and radium-228. US EPA · epa.gov
Marie Curie's notebooks are still radioactive, contaminated mainly with radium-226 (half-life about 1,600 years). Stored at the Bibliotheque nationale de France in lead-lined boxes, they require a waiver and protective gear to handle, and will stay hazardous until around the year 3500.
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