The law of radioactive decay makes a prediction how the number of the not decayed nuclei of a given radioactive substance decreases in time. The red circles of this simulation symbolize 1000 atomic nuclei of a radioactive substance whose half-life period (T) amounts to 20 seconds. The diagram in the lower part of the applet represents the fraction of the not yet decayed nuclei (N/N0) at a given time t, predicted by the following law:
|N = N0 · 2-t/T|
N .... number of the not decayed nuclei N0 ... number of the initially existing nuclei t .... time T .... half-life period
As soon as the applet is started with the green button, the atomic nuclei begin to "decay" (change of color from red to black). You can stop and continue the simulation by using the button "Pause / Resume". In this case a blue point for the time and the fraction of the not yet decayed nuclei is drawn into the diagram. (Note that these points often don't lie exactly on the curve!) If you want to restore the initial state you have to click on the "Reset" button.
It is possible to give the probability that a single
atomic nucleus will "survive" during a given interval.
This probability amounts to
You can't, however, predict the time at which a given atomic nucleus
will decay. For example, even if the probability for a decay within the
next second is
© Walter Fendt, July 16, 1998
Last update: August 28, 1998
Source file (German version): ZerfGes.java