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Sciencetime© 2010
reproduction by permission
of author
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| The rate of radioactive decay
is characteristic of each radionuclide. Scientists talk about this
rate as a radionuclide's radioactive half-life, commonly referred to
as just half-life. It is the time required for the
disintegration of one-half of the radioactive atoms that are present
when measurement starts. It does not represent a fixed number of
atoms that disintegrate, but a fraction.
For example, if there are hundred atoms of
a radionuclide that has a half-life of one minute, there will be one
half that number, or fifty atoms of the original radionuclide left
one minute later. After the second minute, there will be 25 atoms
of the original radionuclide left. The fact that this simple example
points to the existence of 12.5 radioactive atoms after three
minutes, illustrates that half-life is intended to be used for the
very large number of atoms that are found in even small samples of
radioactive materials. 100 atoms aren't going to give off much
radiation!
The half-life tells how quickly the
radioactivity from the radionuclide will decrease. The number of
curies tells how active it is now.
Typical half progression:
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Exponential Decay Equation: Half Life Calculations
N = No1/2 t/c No=
original t= time c = constant of
proportion |
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