How does radioactivity happen?

Al Lowe
Contributor

So the atom is the smallest part of a pure substance, it is like a tiny solar system, and the nucleus has several major parts in it, mostly positive protons and neutral neutrons.
We have all heard a great deal about radioactivity. I would imagine that most people are a bit afraid of radioactivity, mainly because they know almost nothing about it. If you were holding something in your hand, and I told you it was radioactive, you would probably drop it like the proverbial hot potato. There is no need to be frightened about this normal, natural behaviour of atoms. Certainly, large quantities of radioactivity can do your body serious harm, but then so can large amounts of heat, or cold, or wind. In the context of normal living, radioactivity is all around us all the time, at low levels, and there is no need to get all upset about it.
What is radioactivity, anyway? Well, it is the breaking up of the nuclei of atoms. This occurs naturally with some of the heavy atoms - Radium, Polonium., Uranium, etc. When the nucleus of an atom breaks up, it does not always do so in the same way.
There are three major kinds of things emitted from the nucleus of a radioactive atom. These are:
(1) Alpha particles. These are quite large and heavy. (Actually, they are the same as the nuclei of Helium atoms). Each alpha particle has two protons and two neutrons. They therefore contain two positive charges. So, when an alpha particle is lost, the original atom becomes a different atom altogether. These particles are not very penetrating. They can only go through a few centimeters of air before they lose their energy and stop. Then each alpha probably picks up a couple of free electrons, and becomes just an ordinary atom of Helium.
(2) Beta particles. These are entirely different - they are very high speed electrons. Remember that electrons have a negative charge, and that there are only protons and neutrons in the nucleus. So where do these electrons come from? Well, neutrons are neutral - equal number of positive and negative charges. now if some of these neutrons in the nucleus break up, they can release an electron or more. If an electron leaves, it takes its negative charge with it, and that leaves the remainder with a positive charge.
Some of these electrons are travelling at very high speeds - even near the speed of light - and are very penetrating. Notice that the loss of electrons from the nucleus, is the same electrically as the gain of protons, so the atom is changed into a new element altogether.
(3) Gamma Radiation. These are not particle at all, but extremely high frequency, very, very short wave length waves, quite similar to X-rays, but much more penetrating. These can go right through a foot or so of lead, or a couple of kilometers of air, and very easily through your body. This kind of emission from the nucleus does not cause a change in the kind of element it is, because the number of protons hasn’t changed.
So we have three basic forms of radioactivity from naturally radioactive atoms. This also happens with atoms which are made radioactive by man-made external means. But that is another complicated story.
(The diagram shows how the three kinds of radiation behave as they pass through the field of a strong magnet).