Units of Radioactivity:

It was originally based on the disintegration rate of 1g of ²²⁶Ra and called Curie (represented as Ci) after Madame Curie who coined the word 'Radioactivity' and discovered two radioactive elements radium and polonium. Therefore, because of refinement in half-life measurement of ²²⁶Ra it is now described as the quantity of any radionuclide emitting 3.7×10¹⁰ disintegrations per sec (dps).  Ci being a large quantity, practical units of common use are the milli Curie (mCi) and the micro Curie (µCi). In reactor technology, therefore, mega Curie (MCi) is more generally used.  SI unit of radioactivity is Becquerel (Bq) where 1Bq = 1 disintegration per sec (dps). Unfortunately the condition is rather complicated since 1 Bq is too small a quantity. Alternate there is a strong tradition of using Ci more generally.

To the knowledge of half-life of any radionuclide and its disintegration rate, its mass could be computed as described in following instance.