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Naturally occurring rhenium (75 Re) is 37.4% 185 Re, which is stable (although it is predicted to decay), and 62.6% 187 Re, which is unstable but has a very long half-life (4.12×10 10 years). [4]
There are 39 known isotopes of radon (86 Rn), from 193 Rn to 231 Rn; all are radioactive.The most stable isotope is 222 Rn with a half-life of 3.8235 days, which decays into 218 Po
The COVID-19 vaccination campaign in the United States is an ongoing mass immunization campaign for the COVID-19 pandemic in the United States.The Food and Drug Administration (FDA) first granted emergency use authorization to the Pfizer–BioNTech vaccine on December 10, 2020, [7] and mass vaccinations began four days later.