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Formula Radioactive Decay Law Initial number    Decay constant   

Formula
Formula: Radioactive Decay Law
Radioactive decay law - Graph

Number

Unit
Number \(N\) of atomic nuclei not yet decayed at the time \( t \).

Initial number

Unit
Number of atomic nuclei of a radioactive sample present at the beginning, that is at time \( t ~=~ 0 \).

Decay constant

Unit
Decay constant indicates the probability of decay per unit of time. The decay constant determines how fast a nuclide (radioactive substance) decays. Different nuclides decay at different rates.

The reciprocal of the decay constant is the lifetime: \( \tau = \frac{1}{\lambda} \).

Time

Unit
Time at which there are still \( N \) non-decayed atomic nuclei.