What is radiation? | IAEA – International Atomic Energy Agency

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Radiation is energy that moves from one place to another in a form that can be described as waves or particles. We are exposed to radiation in our everyday life. Some of the most familiar sources of radiation include the sun, microwave ovens in our kitchens and the radios we listen to in our cars. Most of this radiation carries no risk to our health. But some does. In general, radiation has lower risk at lower doses but can be associated with higher risks at higher doses. Depending on the type of radiation, different measures must be taken to protect our bodies and the environment from its effects, while allowing us to benefit from its many applications.
Radiation has many beneficial applications but, as in every activity, when there are risks associated with its use specific actions need to be put in place to protect the people and the environment. Different types of radiation require different protective measures: a low energy form, called “non-ionizing radiation”, may require fewer protective measures than the higher energy “ionizing radiation”. The IAEA establishes standards for protection of the people and the environment in relation to the peaceful use of ionizing radiation – in line with its mandate.
Some examples of non-ionizing radiation are the visible light, the radio waves, and the microwaves (Infographic: Adriana Vargas/IAEA)
Non-ionizing radiation is lower energy radiation that is not energetic enough to detach electrons from atoms or molecules, whether in matter or living organisms. However, its energy can make those molecules vibrate and so produce heat. This is, for instance, how microwave ovens work.
For most people, non-ionizing radiation does not pose a risk to their health. However, workers that are in regular contact with some sources of non-ionizing radiation may need special measures to protect themselves from, for example, the heat produced.
Some other examples of non-ionizing radiation include the radio waves and visible light. The visible light is a type of non-ionizing radiation that the human eye can perceive. And the radio waves are a type of non-ionizing radiation that is invisible to our eyes and other senses, but that can be decoded by traditional radios.
Some examples of ionizing radiation include some types of cancer treatments using, X-rays, and radiation emitted from radioactive materials used in nuclear power plants (Infographic: Adriana Vargas/IAEA)
Ionizing radiation is a type of radiation of such energy that it can detach electrons from atoms or molecules, which causes changes at the atomic level when interacting with matter including living organisms. Such changes usually involve the production of ions (electrically charged atoms or molecules) – hence the term “ionizing” radiation.
In high doses, ionizing radiation can damage cells or organs in our bodies or even cause death. In the correct uses and doses and with the necessary protective measures, this kind of radiation has many beneficial uses, such as in energy production, in industry, in research and in medical diagnostics and treatment of various diseases, such as cancer. While regulation of use of sources of radiation and radiation protection are national responsibility, the IAEA provides support to lawmakers and regulators through a comprehensive system of international safety standards aiming to protect workers and patients as well as members of the public and the environment from the potential harmful effects of ionizing radiation.

Non-ionizing and ionizing radiation have different wavelength, which directly relate to its energy. (Infographic: Adriana Vargas/IAEA).
Ionizing radiation can originate from, for example, unstable (radioactive) atoms as they are transitioning into a more stable state while releasing energy.
Most atoms on Earth are stable, mainly thanks to an equilibrated and stable composition of particles (neutrons and protons) in their centre (or nucleus). However, in some types of unstable atoms, the composition of the number of protons and neutrons in their nucleus does not allow them to hold those particles together. Such unstable atoms are called “radioactive atoms”. When radioactive atoms decay, they release energy in the form of ionizing radiation (for example alpha particles, beta particles, gamma rays or neutrons), which, when safely harnessed and used, can produce various benefits.
The process by which a radioactive atom becomes more stable by releasing particles and energy is called “radioactive decay”. (Infographic: Adriana Vargas/IAEA)
Depending on the type of particles or waves that the nucleus releases to become stable, there are various kinds of radioactive decay leading to ionizing radiation. The most common types are alpha particles, beta particles, gamma rays and neutrons.  
Alpha decay (Infographic: A. Vargas/IAEA).
In alpha radiation, the decaying nuclei release heavy, positively charged particles in order to become more stable. These particles cannot penetrate our skin to cause harm and can often be stopped by using even a single sheet of paper.
However, if alpha-emitting materials are taken into the body by breathing, eating, or drinking, they can expose internal tissues directly and may, therefore, damage health.
Americium-241 is an example of an atom that decays via alpha particles, and it is used in smoke detectors across the world.
Beta decay (Infographic: A. Vargas/IAEA).
In beta radiation, the nuclei release smaller particles (electrons) that are more penetrating than alpha particles and can pass through e.g., 1-2 centimetres of water, depending on their energy. In general, a sheet of aluminium a few millimetres thick can stop beta radiation.
Some of the unstable atoms that emit beta radiation include hydrogen-3 (tritium) and carbon-14. Tritium is used, among others, in emergency lights to for instance mark exits in the dark. This is because the beta radiation from tritium cause phosphor material to glow when the radiation interacts, without electricity. Carbon-14 is used to, for example, date objects from the past.
Gamma rays (Infographic: A. Vargas/IAEA).
Gamma rays, which have various applications, such as cancer treatment, are electromagnetic radiation, similar to X-rays. Some gamma rays pass right through the human body without causing harm, while others are absorbed by the body and may cause damage. The intensity of gamma rays can be reduced to levels that pose less risk by thick walls of concrete or lead. This is why the walls of radiotherapy treatment rooms in hospitals for cancer patients are so thick.
Nuclear fission inside a nuclear reactor is an example of a radioactive chain reaction sustained by neutrons (Graphic: A. Vargas/IAEA).
Neutrons are relatively massive particles that are one of the primary constituents of the nucleus. They are uncharged and therefore do not produce ionization directly. But their interaction with the atoms of matter can give rise to alpha-, beta-, gamma- or X-rays, which then result in ionization. Neutrons are penetrating and can be stopped only by thick masses of concrete, water or paraffin.
Neutrons can be produced in a number of ways, for example in nuclear reactors or in nuclear reactions initiated by high-energy particles in accelerator beams. Neutrons can represent a significant source of indirectly ionizing radiation.
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