The Radioactive Decay law states that the number of nuclei undergoing decay per unit time is directly proportional to the number of unchanged nuclei present at that instant.
The formula for Radioactive Decay law is given as,
– (dN / dt) ∝ N
– (dN / dt) = λ N
dN = the number of decay events
dt = interval of time
N = number of atoms
λ = decay constant
Therefore, in a given sample of a particular radioisotope, the number of decay events (dN) expected to occur in a small interval of time (dt) is proportional to the number of atoms present (N). The negative sign indicates that the number of atoms of radioactive element decreases with time.