The becquerel (symbol Bq) is the SI derived unit of radioactivity, defined as the activity of a quantity of radioactive material in which one nucleus decays per second. It is therefore equivalent to s^-1. The older unit of radioactivity was the curie (Ci), defined as 3.7 becquerels or 37 GBq.

In a fixed mass of radioactive material, the number of becquerels changes with time. In some circumstances, amounts of radioactive material are given after adjustment for some period of time. For example, one might quote a ten-day adjusted figure, that is, the amount of radioactivity that will still be present after ten days. This de-emphasizes short-lived isotopes.

SI uses the becquerel rather than the reciprocal second for the unit of activity measure. It was specifically introduced because of the dangers to human health which might arise from mistakes involving the use of reciprocal seconds as the unit. As measured in becquerel units, a more active (and, assuming all other factors to be the same, more dangerous) source has a higher number; this is more intuitively obvious than 1/s, which could lead to confusion.

Definition

1 Bq = 1 s^–1

SI multiples

Origin

The becquerel is named for Henri Becquerel, who shared a Nobel Prize with Marie Curie for their work in discovering radioactivity.

External links

• Derived units on the BIPM web site

SI derived units | Units of radioactivity | Radioactivity

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