What Is Radiation?

Where does it come from? How can it hurt you? How can we avoid it? Quick and Dirty Tips' newest expert, Ask Science, answers these and many other questions about radiation.

Lee Falin, PhD
6-minute read
Episode #1

...it’s only the ionizing kind of radiation that leads to radiation poisoning, and only in very large doses. This is the kind of radiation that the media is usually talking about when they mention things like “radiation leak” and “irradiated super-hero.”

What Is Radioactive Decay?

Sometimes an atom will have too many or too few neutrons in its nucleus, making it unstable, or radioactive. Just like a middle-aged man stepping on the scale for the first time since high-school, these atoms have a strong desire to shed some of their particles in order to reach a stable form. This shedding of particles is called radioactive decay.

Depending on the exact type of atom, atoms going through radioactive decay will emit or kick out alpha particles (a couple of protons stuck to a couple of neutrons) or beta particles (stray electrons) in an effort to become more stable. They can also emit high-energy gamma rays in the process. Radioactive isotopes will often go through an entire series of these changes in order to reach a stable form. Some of these changes can take years, others just a fraction of a second.

How Does Radiation Affect Living Creatures?

Ionizing radiation has enough energy to break chemical bonds and knock electrons out of atoms, changing their net charge. Atoms with missing or extra electrons are called ions, which is why this kind of radiation is called ionizing radiation.

Atoms prefer to have a net charge of 0, so charged ions can get a bit cranky. So cranky in fact, that we sometimes call them free radicals. These revolutionist atoms are much more likely to react with other atoms than their uncharged cousins. Since your body chemistry relies on a finely tuned set of chemical reactions to keep things in balance, having these radical ions around can cause quite a bit of damage inside your cells.

If the damage is too severe, the cells will die. If too many cells are destroyed or damaged at once, such as from a high dose of radiation in a short time period, entire organs can start to fail, eventually leading to death. This is called acute radiation syndrome or radiation poisoning.

If the damage isn’t too severe or widespread, your cells typically have ways of repairing themselves. Unfortunately, sometimes these repairs go wrong, which can still lead to cancer in the long term

How Much Radiation Is Too Much?

So now that you’re cowering in your closet so as to avoid your microwave, you might be wondering just how much is “too much.” This is where things get a bit fuzzy. For one thing, it’s not the amount of radiation you’re exposed to that is the real problem; it’s the amount and kind of radiation that is absorbed over a certain length of time.

Alpha particles coming from outside your body are too large and slow to penetrate your skin. Similarly, beta particles can be blocked by a few layers of clothing. In contrast, gamma rays can penetrate your body without any trouble, causing more damage. On the other hand, if you were to eat or breathe something that emits alpha or beta particles, the soft tissue inside your body would be affected by that radiation.

A lot of the confusion about how much radiation is too much comes from the fact that scientists have about a dozen different units for measuring radiation, depending on exactly what they want to measure about it. More confusing is the fact that some of these units have changed meaning over the years, and some sources get their conversions between the units mixed up.

Rather than make you suffer through several more definitions, I’ll just tell you that there are two measurements which quantify the amount of damage caused by radiation, taking into account how each type of radiation differs in its ability to affect biological tissue.

Most of the world uses sieverts (Sv) for this measurement. Unfortunately, just like its obsession with feet, Fahrenheit, and furlongs, the United States and organizations located there tend to use rems instead of sieverts. Fortunately it is easy enough to convert between the two, as 100 rems equals 1 Sv.

How many sieverts of radiation someone can absorb before they start to have problems actually varies slightly from person to person. Rather than talk more about sieverts or rems however, I’m going to introduce a more familiar analogy to help keep things in perspective...


Please note that archive episodes of this podcast may include references to Ask Science. Rights of Albert Einstein are used with permission of The Hebrew University of Jerusalem. Represented exclusively by Greenlight.

About the Author

Lee Falin, PhD

Dr. Lee Falin earned a B.S. in Computer Science from the University of Illinois, then went on to obtain a Ph.D. in Genetics, Bioinformatics, and Computational Biology from Virginia Tech.