Deutsche Version |

**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/N _{0}) at a given time t,
predicted by the following law:**

N = N
_{0} · 2^{-t/T} |

N .... number of the not decayed nuclei N_{0}... 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 50 % for one half-life period.
In an interval twice as long (2 T) the nucleus survives
only with a 25 % probability (half of 50 %),
in an interval of three half-life periods (3 T) only
with 12,5 % (half of 25 %) and so on.**

**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 99 %, it is nevertheless possible
(but improbable) that the nucleus decays after millions of years.**

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**© Walter Fendt, July 16, 1998**

**Last update: August 28, 1998**

**Source file (German version):**
ZerfGes.java