Radioactive is the process by which an atomic nucleus unstable loses energy by emitting radiation in the form of particles or electromagnetic waves. This degradation or loss of energy, results in an atom of a type known as the parent nuclide to transform an atom of a different type, known as the daughter nuclide. For example: a carbon-14 atom (parent) emits radiation and transforms nitrogen atom for-14 (the daughter). It is a random process on the atomic scale, insofar as it is impossible to predict when an atom will decay, but given a large number of similar atoms, the rate of decline, on average, is predictable.
The SI unit of radioactive decay (the phenomenon of natural and artificial radioactivity) is the Becquerel (Bq). A Bq is defined as a transformation (or decomposition) per second. Since reasonably sized sample of radioactive material contains many atoms, a Bq is a small measure of the activity; amounts of about TBq (terabecquerel) or GBq (gig Becquerel) are commonly used. Another unit (radio) activity is the curia, Ci, which was originally defined as the activity of a gram of pure radium, Ra-226 isotope. At present, it is equal (by definition) the activity of a radionuclide decomposing with a rate of disintegration of 3.7 Ã 1010 Bq. The use of CI is currently discouraged by SI.