Law of decay

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Exponential decrease of a quantity from the initial value N - z. B. the number of radioactive atomic nuclei in a given substance sample - with time t .

The law of decay is the name commonly used in physics for the equation that describes an exponential decrease in quantities over time. In nuclear physics , the law of decay indicates the number of atomic nuclei in a radioactive substance sample that have not yet decayed at a given point in time . This number is


where is the number of nuclei present at the beginning ( ) and the decay constant of the nuclide in question .


If one looks at a radioactive preparation with initially atomic nuclei and the activity , the following applies to the number of nuclei that have not yet decayed during the period :

So after the time there are still some starting cores left.

Average lifespan

The decay constant ( lambda ) is the reciprocal of the mean life , i.e. the time after which the number of atoms has decreased by the factor . ( Tau ) differs from the half-life only by the constant factor :

This results in the following form for the law of decay:

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