The Half-life Period
 
 

The course of the radioactive decay is not strictly determined. On our pages you have dealt with some phenomena of the atom described by probability. It is the same with the radioactive decay. Whether the particular nucleus decays in the next minute or not, is given with some probability, characteristic for each radioactive isotope. Because of that, in a sample of some radioactive material some atoms would decay in the first minute of the observation, some other in the hundredth minute, and some other even in a couple of days or even years. The radioactive decay is described by the laws of statistics. If there is some number of atoms of some radioactive substance, then we can say how many of them would approximately decay in the first or in the hundredth minute. But no way we can say which ones these would be or give the precise number of the decays.

As the time passes the radioactivity of the sample decreases because there are fewer and fewer atoms that can decay, while the probability for each of them remains the same.

If you and your friends are interested in more exactly checking how it goes, than maybe you would like to try with the game described below.


Game: Dice

Each of you should have a cubic dice. The game divides into rounds. In the round each player throws their dice, and if they get one as the result, then they drop out. When starting the game, and after each round, one should write down how many can still play (how many didn't drop out). The game continues until the last player drops out. And then you can draw a diagram. At the horizontal axis you should put the round's number, an at the vertical axis - the number of players that can still play after each round. Of course, the more players, the better diagram. That is why, perhaps it would be the best to play the game at school as a part of a physics lesson.


Game

The game helps to understand how the radioactive decay proceeds: Each player represents an unstable atom, all having the same (1 to 6) probability of the decay (dropping out) in each moment (round). But however knowing the probability, they don't know when the decay will proceed. On the diagram you can see that as the time passes (as the number of unstable atoms decreases), the number of decays in each unit of time decreases.
As an exercise you can play another game in which a radioactive element decays into an also radioactive element, which then decays into a stable one.


symulation

Delphi 4 ActiveX

You should see your Delphi 4 forms or controls embedded in the form below.



The period of time, after which the number of radioactive nuclei of a particular element decreases by 50%, is called the half-life period of that element. For example let's say that in the beginning there are 10 000 atoms of some radioactive element. Then after the period, which equals the half-life of that element, there should be about 5000 such atoms; "should be" not "will be" because the whole process is ruled by probability. The half-life period is characteristic for each isotope, and equals from 10-22 of a second to a couple of billions of years.


Half-life period

That means that some radioactive elements decay almost immediately, and some other need a long time for that.

REMEMBER:
The process of radioactive decay is ruled by probability.
As the time passes, the radioactivity of a sample decreases.
The period of time, after which the number of radioactive nuclei of a particular element decreases by 50%, is called the half-life period of that element.
Each radioactive isotope has a different half-life period.

bar

   TEST no. 8

bar