DECAY CONSTANT

proportionality between the size of a population of radioactive atoms and the rate at which the population decays, as expressed in the equation dN/dt = -lN, in which dN is the decrement of the population, dt is the time increment, l is the decay constant, and N is the population of radioactive isotope at any time. Integration of the decay equation yields N = N0e-lt, which shows that an original population of radioactive atoms, N0, decays exponentially at a rate dependent upon the decay constant. The time required for half of the original population of radioactive atoms to decay is called the half-life. The relationship between the half-life, T1/2, and the decay constant is given by T1/2 = 0.693/l.