­You've probably heard people talk about radiation both in fiction and in real life. For example, when the Enterprise approaches a star on "Star Trek," a member of the crew might warn about an increase in radiation levels. In Tom Clancy's book "The Hunt for Red October," a Russian submarine has a nuclear reactor accident with radiation leakage that forces the crew to abandon ship. At Three Mile Island and Chernobyl, nuclear power plants released radioactive substances into the atmosphere during nuclear accidents. And in the aftermath of the March 2011 earthquake and tsunami that struck Japan, a nuclear crisis raised fears about radiation and questions about the safety of nuclear power.

­Nuclear radiation can be both extremely beneficial and extremely dangerous. It just depends on how you use it. X-ray machines, some types of sterilization equipment and nuclear power plants all use nuclear radiation -- but so do nuclear weapons. Nuclear materials (that is, s­ubstances that emit nuclear radiation) are fairly common and have found their way into our normal vocabularies in many different ways. You have probably heard (and used) many of the following terms:

­All of these terms are related by the fact that they all have something to do with nuclear elements, either natural or man-made. But what exactly is radiation? Why is it so dangerous? In this article, we will look at nuclear radiation so that you can understand exactly what it is and how it affects your life on a daily basis.