The strontium unit is a unit used to measure the amount of radioactivity from strontium-90, a radionuclide found in nuclear fallout, in a subject's body; as the human body absorbs strontium as if it were calcium, incorporating it into the skeleton, its presence is very common. One strontium unit is equal to one picocurie from strontium-90 per gram of calcium (37 becquerels per kilogram) in the subject's skeleton.
The United States National Academy of Sciences holds that the maximum safe measure of strontium-90 in a person is one hundred strontium units (3700 Bq/kg). The average American is estimated to have three to four strontium units.
The strontium unit was formerly known briefly as the sunshine unit, a term promoted by the United States Department of Defense until public ridicule brought about its disuse. (Among the sources of this outcry was a George Carlin performance, released on the CD "Parental Advisory: Explicit Lyrics", during a passage on governmental euphemisms for dangerous or unethical activities: "The Pentagon has actually begun measuring nuclear radiation in something they call 'sunshine units'!")
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