Decay Rate (Half-Life)
Each radionuclide decays at its own unique rate which cannot be altered by any chemical or physical process. A useful measure of this rate is the half-life of the radionuclide. Half-life is defined as the time required for the activity of any particular radionuclide to decrease to one-half of its initial value. In other words one-half of the atoms have reverted to a more stable state material. Half-lives of radionuclides range from microseconds to billions of years. Half-life of two widely used industrial isotopes are 74 days for iridium-192, and 5.3 years for cobalt-60. More exacting calculations can be made for the half-life of these materials, however, these times are commonly used.
The applet below offers an interactive representation of radioactive
decay series. The four series represented are Th232, Ir192, Co60,
Ga75, and C14. Use the radio buttons to select the series that
you would like to study. Note that Carbon-14 is not used in radiography,
but is one of many useful radioactive isotopes used to determine
the age of fossils. If you are interested in learning more about
Carbon-14 Dating, follow this link: Carbon-14
The Sequence Info button displays a chart that depicts the path
of the series with atomic numbers indicated on the vertical axis
on the left, and the number of neutrons shown along the bottom.
Colored arrows represent alpha and beta decays. To return to the
main user interface, click the "Dismiss" button.
Initially, a selected series contains all parent material, and
the amount is represented by a colored bar on a vertical logarithmic
scale. Each line represents a factor of ten. In order to step
forward through the sequence by a specified number of years, you
may type the appropriate number into the "Time Step"
field and hit "Enter." A negative time step will backtrack
through the sequence.
You may choose a step interval in years and progress through each step by pressing the "Enter" key. The "Animate" button will
automate the progress through the series. You can either choose
a time step before you animate or leave it at zero. If the time
step is left at zero, the system will choose time steps to optimize