Radiation refers to the spreading of energy by waves or particles through a medium or a vacuum, like space. Radiation can have two sources, electromagnetic waves or particles. Electromagnetic waves are photons, and they cover a wide range, from radio waves to gamma rays. Radiation by particles is produced by parts of the atom that break away from it in a disintegration process.

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    Electromagnetic radiation has an associated wavelength. Shorter wavelengths have more energy, and larger wavelengths have less energy.

    Examples of radiation

    Examples of radiation and associated energy include:

    • Sunlight: electromagnetic radiation is a wide spectrum. Part of this spectrum covers what we call visible light (detectable by our eyes). It has moderate energy.
    • Radio: long-wavelength radiation allows communication at large distances. Radio waves have lower energy than sunlight.
    • Microwaves: an example of medium wavelength radiation, microwave radiation is used for radar, communications, and cooking. Microwaves also have lower energy than sunlight.
    • X-rays: high-energy radiation with a very short wavelength is used in medicine to see inside the body.
    • Particle radiation: subatomic particles ejected from an atomic nucleus travel at high speeds with high energy. If they have enough energy, they can break atoms or chemical bonds.

    How does radiation occur?

    For radiation to happen, an atom needs to receive an excess of energy. The energy received alters the particles and makes the atom release radiation. The steps for radiation to occur when releasing a photon are as follows:

    1. The atom is in a non-stable state because it has an excess of energy. This excess is caused by a photon carrying electromagnetic energy, which impacts an electron.
    2. The non-stable state is also called an ‘excited’ state. Atoms will always seek balance by releasing any excess energy, in this case, the electron will seek to release the energy excess.
    3. Excess energy will be released as electromagnetic waves (photons). The energy of the photon released will be linked to the orbit of the electron that was excited.
    4. The radiation emitted in the form of photons is an electromagnetic wave and its frequency will be linked to the energy released. Larger energies released will correspond to larger frequencies.

    Atoms also release radiation in the form of particles such as neutrons, alpha particles, and beta particles. The process in which radiation is released is known as radioactive decay. In this case, the forces that keep the atom together are out of balance, and the atom releases particles seeking stability. The kinetic energy of the particles is linked to their energy.

    Radiation. Energy and particle release. StudySmarter

    Figure 1. Ways that radiation can occur. Source: Manuel R. Camacho, StudySmarter.

    How does radiation work?

    Radiation is a form of energy – a wave or particle with a charge moving at a certain speed. As a form of energy, it can inject energy into an atom, break it, or move its particles. Radiation can also come from a non-stable atom, as in the following examples:

    • An electromagnetic wave injecting energy into an electron moving around an atom, altering its movement.
    • The impact between a fast-moving electron and an atom, resulting in an electron being pushed out.
    • An atom with a large number of particles in its centre, breaking apart and releasing energy.

    There are several types of radiation, several radiation sources, and also many uses of radiation.

    Classification of the radiation by electromagnetic waves

    Radiation by electromagnetic waves can be classified in several ways by considering its wavelength, energy, or source.

    One characteristic of radiation is its wavelength. Shorter wavelengths contain more energy, while longer wavelengths have less. Radiation by electromagnetic waves has different names, depending on its wavelength, as can be seen in the illustration below.

    Radiation. Wavelength. StudySmarter

    Figure 2. Approximate wavelengths for several kinds of electromagnetic radiation. Source: Manuel R. Camacho, StudySmarter.

    Radiation can be ionising or non-ionising. This depends on the amount of energy the radiation has.

    • Ionising: if the radiation can change the atomic structure by moving electrons or particles out of the atom, it is called ionising radiation.
    • Non-ionising: if the radiation cannot change the atomic structure but can make electrons move their positions up and down, it is known as non-ionising radiation.

    Radio waves are an example of non-ionising radiation, while UV radiation from the sun and x-rays are both types of ionising radiation.

    Radiation is also classified into waves or particles, depending on the element that carries the energy.

    • Waves: these belong to the electromagnetic spectrum and range from radio waves to visible light to highly energetic gamma rays produced by faraway stars.
    • Particles: the other source of radiation is particles, which are knocked out from atoms by other particles. This form of radiation consists of electrons, neutrons, and protons that fly off at high velocities.

    Sources of radiation

    Radiation can come from natural sources or artificial sources created by technological applications.

    Natural sources include radiation that reaches the earth from the sun and stars and radiation released by the natural disintegration of atoms in the earth’s crust or even living beings.

    Artificial sources include radar systems, microwaves, sources of lighting, heating devices (heat radiation), TV sets, wireless internet and telecommunication devices (including mobile phones), many artificially created short-lived isotopes used in medicine, and many other sources.

    Unstable nuclei and atom disintegration

    Atomic nuclei are a source of radiation, which occurs when an atom breaks. For an atom to break, it must be unstable, and when it does break, it usually becomes a lighter and more stable element.

    Some elements have high stability and can remain the same for billions of years. Others only last a few seconds.

    Uranium has a high number of protons, electrons, and neutrons, making it a heavy element. Uranium 238 has 92 protons and 146 neutrons in the nucleus and 92 electrons moving around it. Uranium 238 has enough protons to make it unstable, and it will disintegrate over time. When that happens, it releases two protons and two neutrons glued together, transforming it into Thorium 234.

    The two protons and two electrons glued together are called alpha particles, which have the following symbol: \(^{4}_{2}He\)

    The disintegration also generates energy in the form of electromagnetic waves. The released alpha particle and the waves are the resulting radiation. The general reaction is as follows:

    \(238 U \rightarrow 234 Th + ^{4}_{2}He + energy\)

    Uses of radiation

    Radiation has many uses, including medicine, communications, sterilisation, energy production, and others.

    • Medicine: radiation therapy involves the use of focused doses of radiation to kill tumour cells in patients.
    • Aviation: radars use electromagnetic radiation to detect aeroplanes. The radar helps to track, detect, and direct the air traffic over any given territory.
    • Microwaves: these use radiation to induce vibration on the water molecules. The more they move, the more heat they produce.
    • Medical screening tests: MRI scans use radio waves to produce detailed images of the structures inside the human body. CT scans and x-rays use the same principle, but their photons have higher energy.
    • Energy: radiation is used in fission reactors to produce energy.
    • Communication: mobile phone and satellite communications use radio waves to transmit data.
    • Sterilisation: radiation is used in several industries to kill germs and insects.

    Radiation. Radiotherapy. StudySmarter

    Figure 3. Radiotherapy is used to treat cancer.

    Radiation - Key takeaways

    • Radiation is the emission of electromagnetic energy by waves or particles from an atom.
    • Radiation is classified by its source, wavelength, and energy.
    • Radiation has many uses that range from medicine to energy and communication devices.
    • Sunlight is a form of electromagnetic radiation perceived by our eyes.
    • Unstable nuclei can emit radiation as they expel energy and particles.
    Frequently Asked Questions about Radiation

    What is radiation?

    Radiation is the emission of energy or particles from an atom.

    How many types of radiation are there?

    There is radiation by particles and radiation by electromagnetic waves.

    How does radiation work?

    Radiation is the emission of energy or particles by an atom. To emit these, an atom must have an excess of energy. This is released either as waves or in the form of particles. Atoms can also produce radiation when they are hit by another particle with enough force that causes them to break up.

    Test your knowledge with multiple choice flashcards

    What is radiation?

    Which of these are natural sources of radiation?

    What is ionising radiation?


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