Electromagnetic radiation

Electromagnetique radiation definition

Electromagnetic radiation or electromagnetic waves is a form of energy emitted and absorbed by charged particles, which exhibit wave-like behavior as they travel through space.

Electromagnétique radiation meaning

Electromagnetic radiation is a flow of energy at the speed of light through space or through a material medium, and electromagnetic radiation has electric and magnetic fields, which together form an electromagnetic wave, and an electromagnetic wave is characterized by its intensity and frequency in the change with time of electric and magnetic fields, and the frequency range of electromagnetic radiation extends from low values ​​Extremely high values ​​of ultraviolet light, x-rays and gamma rays over the range of radio waves, television waves, microwave ovens up to visible light and beyond are extremely high values ​​of ultraviolet light, x-rays and gamma rays.

Photosynthesis to plant life or use by zooplankton, and interference from electromagnetic rays in many areas of daily life, including microwaves, directing airplanes, televisions and incandescent lights, and the use of these rays is also widely used in medicine.

Waves and fields

Electromagnetic radiation occurs when an atomic particle, such as an electron, is accelerated by an electric field, causing it to move. This movement produces oscillating electric and magnetic fields that travel perpendicular to each other in a bundle of light energy called a photon.

Photons travel in homogeneous waves at the fastest possible speed in the universe: 186,282 miles per second (299,792,458 meters per second) in a vacuum, also known as the speed of light. Waves have specific properties, such as frequency, wavelength, or energy.

Electromagnetic waves are formed when the electric field (indicated by red arrows) interferes with the magnetic field (indicated by blue arrows). The electric and magnetic fields of an electromagnetic wave are perpendicular to each other and in the direction of the wave.

Wavelength is the distance between two successive crests of a wave, measured in meters, or parts of it. Frequency is the number of waves that form over a specific period of time and is generally measured as the number of wave cycles per second, or hertz.

A short wavelength means that the frequency will be higher because a cycle can pass over a short period of time, similarly, a longer wavelength has a lower frequency because each cycle takes longer to end.

Electromagnetic radiation spectrum

Electromagnetic radiation travels in a vacuum at a constant speed which is the speed of light and its value is 3 x 108m / s2. These rays travel in a vacuum and transfer energy from the source to the receiver. These rays were discovered in stages, because the scientist Hertz 1887 was the first to work in this field and it was at this time only radio rays and visible rays, then the rest of the electromagnetic spectrum was discovered thanks to observations and physical phenomena.

Electromagnetic radiation has a wavelength l and a frequency n which determine its properties. The speed of electromagnetic radiation is related to frequency and wavelength through the equation: c = n.l

As it is clear in the figure opposite, a diagram of the whole electromagnetic spectrum, starting from the radio waves of long wavelength and low frequency, then the microwave region, the infrared region, the region visible, then the UV region, then the X-ray region, then the gamma-ray region. This sequence is a function of the increasing frequency of these waves. Each region of the electromagnetic spectrum has characteristics that distinguish it from one another, and as a result, different applications of these rays have resulted. For your information, the visible spectrum region is what Almighty God has given us the ability to see, and it is the region that the retina responds to in order to see the things around us.

Types of electromagnetic radiation

  • Radio rays : The source of this type of rays is from the stars, and humans can also generate them in order to transmit audio data.
  • Microwave rays : These rays are emitted by stars and galaxies, and humans use them to heat food and transmit data.
  • Infrared rays : These rays are emitted by thermal bodies, which include the bodies of living organisms, as well as by dust and gases between stars.
  • Visible spectrum : a small part of the spectrum that the human eye can see. This spectrum is emitted by stars, lamps and certain chemical reactions.
  • Ultraviolet rays : UV rays are emitted by stars such as the sun, and these rays are harmful to humans because they can cause sunburn, skin cancer and cataracts.
  • X rays : These rays are emitted by hot gases and are used by humans in diagnostic imaging.
  • Gamma rays : These rays are emitted from the universe and can be used in imaging such as X rays.

Electromagnetic radiation detector

The radiation penetrates inside the detector, symbolized in Figure 1 by a space (the active area) between the two electrodes (anode + cathode). The radiation meets and tears in its course electrons between the atoms of the medium. During ionization, the particle loses some of its energy (which is the energy it takes to tear off an electron). This particle gradually slows down until it is stopped. Under the effect of an electric field, electrons are attracted to the anode while positively charged ions are collected by the cathode. A very weak electric current is then created in the circuit connecting the two electrodes. This current of a few micro-amps is sent to the measurement chain

There are two possible modes of operation for a radiation detector :

  • The current mode of operation : In this case we are measuring the average direct current produced by the detector. This operating mode is used for dosimetry detectors and in monitoring the power of nuclear reactors as well as the various radioactive sources …
  • Pulse mode of operation : it is the recording of the outgoing electrical charges of each individual interaction in the detector instead of having the average current created by several interactions. When the detector is operating in this mode, the amplitude of each pulse carries information about the charge generated by the interaction of radiation in the active area of the detector. This mode is recommended for identifying multiple sources

Note: In the absence of any incident radiation or active source, the detector placed under normal conditions of use delivers a very low current called dark current. This current or also called « noise » has an internal origin, it is thermal excitation as well as an external origin which comes back to the ambient thermal radiation. The noise is particularly important in the infrared range where it sometimes becomes necessary to cool the detector.

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