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Alpha-Beta-Gamma radiation

By George W. Dowell

Alpha and Beta particles are actually physical particles of matter. The Alpha is two protons and two neutrons, and consequently is relatively very heavy and slow and carries a double positive charge.. A Beta is simply an electron and has a negative charge. The Beta may be moving from very slow to very fast, and the speed is an indication of it's "energy level". Gamma Radiation is a true electromagnetic energy, and moves at or near the speed of light.

Alphas can barely penetrate anything, not even a piece of paper. Betas do a bit better but still can only penetrate a thin piece of aluminum. Gammas on the other hand can penetrate inches of lead and feet of most other things. These differences can be used to our advantage if wee seek to determine the nature and composition of any "radiation" we are investigating.

To discriminate the types of radiation, all you need to do is understand the characteristics of your particular probe, and have a few pieces of "absorber" material on hand. If the radiation is stopped by a single piece of typing paper, it is undoubtedly Alpha particles. If it takes a piece of tin foil or a very thin aluminum sheet to stop most of it, you are probably looking a Betas. Of course the tin foil also stops all Alphas too. Gamma rays will easily pass through steel, aluminum and it takes 1" of lead to stop even 1/2 of it.

Nothing actually "stops" Gamma rays, it is a matter that 1/2" of lead statistically blocks 1/2 of the rays, the next 1/2" will block 1/2 of what's left etc. etc. until the remaining ray is insignificant. Each absorbing material, be it lead, earth, water whatever has a statistical "half-thickness" assigned to it.

In real life, radioactive materials seldom emit only one kind or energy level of radiation, but rather a mixture. It is this characteristic mixture that helps to identify and quantify the particular material being observed. My own attempts a real Gamma Spectrometry, indeed at quantitative measurements in general have been met with a lot of disappointment, but I do feel that I can at least identify the major types of radiation rather easily now.



Thinking of buying a surplus CDV-700 or 715 detector? Be sure to read our report first.