The rate at which an unstable nucleus decays depends only on what type of nucleus it is.
This decay is a random process. This means that if we take a sample of unstable nuclei we cannot know when any individual nucleus is going to decay.
However we can measure what we call the half life (written as T or t1/2) for the element in the sample.
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The half life of an element is defined as: (a) The average time taken for half the original number of nuclei in a sample of an element to decay (b) The average time taken for the activity of a radioactive source to fall to one half of its original value |
The decay constant l and half life
Decay constant (l) = 0.693/T