To understand the risks of radiation, we must begin at the atomic level to see what radiation does, and we have to consider the different kinds of radiation and, most important, the dose. This is going to be a somewhat technical chapter, but I hope you will stick with it. Ifyou do, you will have a much better understanding ofwhat radiation actually does to cells and how different types of radiation have different consequences.

Let’s begin with the various kinds of radiation and how they interact with atoms. There are four kinds of radiation associated with nuclear power—a, p, у and neu­trons—as discussed in Chapter 6. X-rays and у rays are basically the same type of radiation, and they interact with matter in exactly the same way, so I will con­sider them as one type: electromagnetic radiation. Their interactions with matter depend on their particle nature as photons with energy hf. The rules governing electromagnetic radiation are different from the rules governing charged particle radiation, such as a and p radiation. Neutrons are uncharged particles, so they interact in a different way from charged particles and electromagnetic radiation.

The most damaging thing that radiation can do to atoms is to ionize them— that is, to kick an electron out of an atomic orbit—leaving an atom with a positive

charge: an ion. Ionized atoms can break chemical bonds or change the nature of a molecule. Photons such as X-rays or у rays are energetic enough to ionize atoms and give the electron a lot of kinetic energy, so they are called ionizing radia­tion. Ultraviolet light, another form of electromagnetic radiation, does not have enough energy to ionize atoms, so it is called non-ionizing radiation—though it can still be hazardous but for totally different reasons.