Strontium unit Strontium unit 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. Since 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
2019 redefinition of SI base units seven base units whose definitions are unconstrained by that of any other unit and another twenty-two named units derived from these base units. The metre was redefined in terms of a wavelength of krypton-86 radiation, making it derivable from universal natural phenomena, but the kilogram remained defined in terms of a physical prototype, leaving it the only artefact upon which the SI unit definitions depend. Although designed for long-term stability, the masses of the kilogram prototype and its secondary copies have shown small variations over time relative to each other, and they are not thought to be adequate for the