section_path: Rates
section_name: Rates
paragraph_text: Rates
  
  The decay rate, or activity, of a radioactive substance is characterized by the following time-independent parameters:
  
  Although these are constants, they are associated with the statistical behavior of populations of atoms. In consequence, predictions using these constants are less accurate for minuscule samples of atoms.
  
  In principle a half-life, a third-life, or even a (1/√2)-life, can be used in exactly the same way as half-life; but the mean life and half-life t have been adopted as standard times associated with exponential decay.
  
  Those parameters can be related to the following time-dependent parameters:
  
  These are related as follows:
  
  where N is the initial amount of active substance — substance that has the same percentage of unstable particles as when the substance was formed.