# decay constant

## decay constant

noun Physics.
the reciprocal of the decay time.
Also called decay rate,

Origin:
1930–35

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decay constant n.

Symbol λ The constant ratio for the number of atoms of a radionuclide that decay in a given period of time compared with the total number of atoms of the same kind present at the beginning of that period. Also called disintegration constant, radioactive constant.

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decay constant

proportionality between the size of a population of radioactive atoms and the rate at which the population decreases because of radioactive decay. 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=lambdaN, where lambda is the decay constant. Integration of this equation yields N=N0elambdat, where N0 is the size of an initial population of radioactive atoms at time t=0. This shows that the population decays exponentially at a rate that depends on 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/lambda.