There are 3 measuring units :

The Becquerel, from the French physicist Henri Becquerel (1852-1908), "Bq" for short,  measures the activity of a radioactive source, that is the number of disintegrations per second.  1 Bq equals 1 disintegration per second.


The Curie (Ci), from the French couple of scientists Pierre and Marie Curie (1859-1906 and 1867-1934) is the old measuring unit for radioactivity, but it is still widely used. 1 Ci equals the activity of 1 g of radium (an element discovered by the Curies) and represents 37 billions of disintegrations per second (or 3.7 1010 Bq).


The Gray, from the English scientist Louis Harold Gray (1905-1965), ‘’Gy’’ for short, measures the amount of energy transferred to matter in case of exposure (per mass unit). 1 Gy equals the absorption of 1 joule per kilogram.


The Sievert, from the Swedish scientist Rolf Sievert (1896-1966),  ‘’Sv’’ for short, measures the biological effects of exposure on the organism.

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