Ionising radiation: Introduction

When something smashes into us, we might get a bruise or a cut if it's big enough and thrown hard enough, that is. When something tiny and lightweight hits us, we barely notice it. But if we're hit by something that's really, really tiny but still hits us very, very hard with a lot of energy, it can make a special kind of damage. This is what happens when we're hit by ionizing radiation. Ionizing radiation is called just that because it has so much energy, that it can break loose electrons from atoms and molecules, turning them into ions.

That can hurt people and other living things. These signs warn us about ionizing radiation. How badly the radiation will hurt us, depends on which organs are exposed and how much radiation they are exposed to. ​ ​If the dose of radiation is greater, there is more damage. If you are exposed to radiation your risk of cancer later in life increases. Your reproductive cells, gametes, can be damaged.

And if a pregnant woman is exposed to radiation, the fetus can be injured or die. A very high dosage of radiation could lead to seizures, cramps, or immediate death. Ionizing radiation affects non-living things as well. Metals for example, get brittle and breakdown faster. Electronics can be damaged and some forms of radiation can make materials radioactive so that they themselves start radiating. ​ ​Here's an atomic nucleus that is radioactive.

Being radioactive means that it will fall apart, it will decay. The decay of a nucleus means that a small bit of it comes off and flies away. When the nucleus decays, it changes, and it gets a different number of protons and with a different number of protons the atom turns into a different element. The small piece that comes off is thrown away with an enormous energy. This nucleus is emitting ionizing radiation.

Radioactive decay can cause three different forms of ionizing radiation. Two of them consist of particles. One is electromagnetic radiation. ​ ​The three forms of radiation have different properties, but they are all ionizing. Alpha radiation emits particles with two protons and two neutrons, an alpha particle. Alpha radiation doesn't reach very far.

It can't travel very far through the air and it's not able to get through human skin. But if you eat or inhale something that emits alpha radiation, it can hurt you because then there's no protective skin and the radiation reaches the cells inside your body directly. Beta radiation is also emitting particles, either an electron or a positively charged positron. Both of them are called beta particles. Beta radiation reaches farther than alpha radiation.

It can get through the skin, but not very far into the body. Just as with alpha radiation, beta radiation is mostly harmful when it comes from inside the body. Substances that emit beta radiation can accumulate in the body for a long time, often in the thyroid gland where they damage nearby cells. The third form of ionizing radiation that can come from a decaying atomic nucleus is gamma radiation. Gamma radiation is a form of electromagnetic radiation with very high frequency and energy.

Gamma radiation is not particles. It doesn't consist of fragments of the nucleus but of energy in the form of electromagnetic waves, just like ordinary light or radio waves. But gamma radiation has an extremely high frequency and thus a short wavelength. Each gamma ray therefore has a lot more energy than an ordinary ray of light. That's what makes it ionizing.

Gamma radiation reaches farther than alpha and beta radiation. To stop it you need a sheet of lead several centimetres thick. ​ ​Three different kinds of radiation that have two things in common, all three are created when the nucleus of a radioactive element decays and all three are ionizing. We call them alpha, beta, and gamma radiation from the first three letters of the Greek alphabet.