${\displaystyle \lambda =-\frac{1}{N}\times \frac{\text{d}N}{\text{d}t}}$

Note 1 to entry: The decay constant is expressed in reciprocal seconds (s⁻¹).

Note 2 to entry: The decay constant may be considered the total probability of radioactive decay (disintegration and/or nuclear transition).

Note 3 to entry: This entry was numbered 393-14-18 in IEC 60050-393:2003.