Sentence:  I was at Good Samaritan Hospital in Los Angeles for a radioactive iodine scan, this one at diagnostic levels—less radiation than the therapeutic levels I would eventually endure. I drank my first <WSD>atomic cocktail</WSD>: a vial of liquid radioactive iodine diluted in what seemed like gallons of water. 
Meaning of the word marked with <WSD> tags:  A drinkable liquid containing a radioactive substance, used in health care either as a diagnostic aid or as a treatment, especially for cancer of the thyroid.