Radiation is the decay of an unstable atom by losing or emitting energy as it tries to achieve a stable state.
The emission is spontaneous and is a purely random process. This property of randomness
can be used in random number generators in many types of applications.
The SI unit of Radioactivity is the Becquerel (Bq) and is defined as the number of Disintegrations per Second. Another common unit is the Curie (Ci).