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Becquerel, Bq

The unit of activity that expresses how many particles are released from material because of radioactive decay during a period of time. The object has an activity of one becquerel when one particle is released per second. It is a small unit and is mostly used with the kilo, mega, or giga prefix. The activity is expressed in becquerels mostly for long-lived isotopes, as the activity changes in time. The approximate activity of the human body is around 7,000 Bq. This is caused largely by radioactive decay of unstable isotope of potassium 40. The unit was named after the scientist Henri Becquerel. The old activity unit was curie, defined as the activity of one gram of uranium. 1 curie equals 37 billion becquerels.

Radioactivity in becquerels of various objects

Object Activity (Bq)
Water (l) 15
Coal mined in the USA (kg) 174
Brazil nuts (kg) 460
Tea (kg) 700
Coffee (kg) 1,000
Granite (kg) 1,000
Fly ash from coal mined in the USA (kg) 1,200
Whisky (l) 2,000
Australian superphosphate (kg) 3,000
Human body (70 kg) 7,000
Household smoke detector containing americium 30,000
Uranium ore (kg) 25,000,000
Vitrified nuclear waste from a nuclear power plant 50 years after irradiation (kg) 10,000,000,000, 000