The decay constant (symbol: λ and units: s−1 or a−1) of a radioactive nuclide is its probability of decay per unit time. The number of parent nuclides P therefore decreases with time t as dP/P dt = −λ. The energies involved in the binding of protons and neutrons by the nuclear forces are ca.
The rate of disintegration is proportional to the number of atoms at any point in time and the constant of proportionality is called the radioactivity decay constant. The radioactive decay constant for Radium B is approximately 4.3 × 10−4 s−1.
Suppose N is the size of a population of radioactive atoms at a given time t, and dN is the amount by which the population decreases in time dt; then the rate of change is given by the equation dN/dt = −λN, where λ is the decay constant.
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