With many of the sources you encounter in everyday life, the amount of radiation is so low that you don’t have to worry about it. But ionizing radiation can also be dangerous, because these free electrons interact with the molecules in the cells and tissues of the human body. Adding an extra electron can break the chemical bonds that hold molecules together. That’s why the radioactive materials associated with nuclear weapons and power plant meltdowns can increase the risk of cancer.
There are four types of ionizing radiation: alpha, beta, gamma and neutron radiation. Here’s what’s going on with each type and how to detect them.
In 1896, no one really knew anything about radiation. They didn’t know if it was a particle or some kind of electromagnetic wave, like light. Therefore, they decided to use the term “rays” in a general sense, such as rays of light. That’s how we get residual terms like alpha rays or gamma rays.
But – SPOILER ALERT – alpha rays are not waves. They are actually electrically charged particles. An alpha particle consists of two protons and two neutrons. This means that an alpha particle is a helium atom without the electrons. (Yes, they should have called them “helium particles,” but no one knew what was going on.)
How can you tell that it is alpha radiation and not some other type? The answer is that alpha particles can easily be blocked by something as thin as a sheet of paper. So if you have a source that produces alpha particles, you can shield the detector – such as photographic film – with a very small amount of material.
The reason alpha particles are blocked so easily is that, because they are so heavy, they are often thrown from the radioactive source at relatively low speeds. Furthermore, with an electric charge equal to two protons, there is a significant electrostatic force between the alpha particle and the positive core of the shielding paper. (We call this a surcharge of 2eWhere e is the fundamental charge of an electron or proton.) It doesn’t take too many of these atoms in the paper to actually stop the alpha particle.
Do you know what else can stop an alpha particle? Human skin. That is why alpha radiation is often considered the least harmful type of radiation.
In 1899, Ernest Rutherford classified three types of radiation: alpha, beta and gamma. Although the alpha particles were easily stopped, beta and gamma particles could pass through a certain amount of metal shielding and penetrate further into the material because they have a much lower mass. In fact, beta particles are electrons: the fundamental particles with a negative charge. The mass of an alpha particle is more than 7,000 times greater than that of a beta particle. This means that beta particles of very low mass can be emitted at very high speeds, allowing them to penetrate objects, including the human body.
Gamma rays Are actually rays, not particles. They belong to the third class of radiation and are a type of electromagnetic waves, just like visible light.
However, the light you can see with your eyes has a wavelength between 400 and 700 nanometers, while gamma rays have a much smaller wavelength. A typical gamma ray may have a wavelength of 100 picometers. (Note: 1 picometer = 10-12 meters, and 1 nanometer = 10-9 meters.) This means that the wavelength of gamma rays can be about 1000 times smaller than that of visible light. With such a small wavelength and a very high frequency, gamma rays can interact with matter at very high energy levels. They can also penetrate quite deeply into most materials, so a large portion of lead is usually required to block these radiations.