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1. In medicine, a liquid solution that contains one or more radioactive elements, which is swallowed orally and used in the diagnosis and/or treatment of disorders, especially cancer and diseases of the thyroid. We are just going to administer a sort of atomic cocktail to track the disease's progress. That way, we can better gauge what course of action to take.
2. An alcoholic drink composed of vodka, brandy, champagne, and sherry. Created in Las Vegas, Nevada, and named after the nuclear tests conducted in the state during the 1950s. Barkeep, I want something that will knock my socks off. Fix me an atomic cocktail!