EXPERIMENT 7: Demonstrate How Radioactivity Can Be Shielded

THINGS YOU NEED: Equipment from Experiments 3 and 4 (see also the last paragraph in this section). Small pieces of different materials such as paper, aluminum foil plastic, and wood.

Certain radioactive emissions can be dangerous. Thus, nuclear power plants have extensive shielding to protect employees and people living in nearby communities. This

shielding is so effective that you can spend your whole life living next to a nuclear power plant and receive only about the same total dose of radiation as if you had taken a chest X-ray.

This experiment demonstrates the radioactivity shielding properties of various materials. But before starting it, you should know a little more about the three kinds ofradiation given off by a radioactive substance: alpha rays, beta rays, and gamma rays. As we said earlier, alpha rays are made up of alpha particles, and each alpha particle is identical, in all respects, to the nucleus of a helium atom. Because of its relatively large size (compared with other forms of radiation) an alpha particle is easily blocked by many common materials.

Similarly, beta rays are made up of beta particles. A beta particle is actually an electron. It is much smaller than an alpha particle and, therefore, has greater penetrating power. Denser materials are needed to stop beta particles.

But of the three, gamma rays have the greatest penetrating power; so they require the densest shielding materials. Curiously, gamma rays are not made up of particles. There is no such thing as a gamma particle. Gamma rays consist of individual packets of energy called photons.

Now to work. The two experiments you performed earlier, Experiments 3 and 4, are easily modified to demonstrate how alpha rays can be shielded. All you need do is cover the opening on your alpha source with different materials before you perform the experiments.

If a particular material blocks alpha rays, the static electricity around the electroscope (Experiment 3) will