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Electromagnetic radiation

Electromagnetic radiation

In physics, electromagnetic radiation (or gamma γ radiation) is the radiation of energy in the electromagnetic field. It is a phenomenon both wave and corpuscular:

The wave phenomenon is given by a wave in the electric field and in the magnetic field and is described mathematically as a solution of the wave equation, obtained in turn from Maxwell's equations according to the theory of classical electrodynamics.

corpuscular nature, or quantified, can instead be described as a stream of photons that, in a vacuum, travel at the speed of light. This fact was made known by the modern studies of physics at the beginning of the 20th century, which recognized in the photon the mediator associated with electromagnetic interaction, according to the Standard Model.

Electromagnetic radiation can spread in a vacuum, such as interplanetary space, in less dense environments, such as the atmosphere, or in guide structures, such as waveguides. The technological applications that exploit electromagnetic radiation are varied. In general, two macro families of applications can be distinguished: in the first one there are the electromagnetic waves used to transport information (radio communications such as radio, television, mobile phones, artificial satellites, radars, radiographs), in the second those to transport energy , like the microwave.

Characteristics of electromagnetic radiation

The main characteristics of electromagnetic radiation are considered frequency, wavelength and polarization.

The wavelength is directly related to the frequency through the propagation velocity (group) of the radiation. The speed of group propagation of electromagnetic radiation in a vacuum is equal to the speed of light, in other environments this speed is lower. The phase velocity of the electromagnetic radiation in a vacuum is also equal to the speed of light; in various media, it can be less or greater than the speed of light.

The description of the properties and parameters of electromagnetic radiation is generally treated by electrodynamics, although certain more specialized sections of physics are involved in the radiation properties of individual regions of the spectrum (partly this happened historically, partly due to significant details, especially in relation to the interaction of radiation of different ranges with matter, and partly also the details of the problems applied) These more specialized sections include optics (and their sections) and radiophysics.

High energy physics deals with the hard electromagnetic radiation of the shortwave end of the spectrum; according to modern concepts, at high energies, electrodynamics ceases to be independent, combining in a theory with weak interactions and then, at even higher energies, as expected, with all other measurement fields.

There are theories that differ in details and degrees of generality, which allows modeling and studying the properties and manifestations of electromagnetic radiation. The most fundamental of the complete and verified theories of this type is quantum electrodynamics, from which, through various simplifications, it is possible in principle to obtain all the theories listed below, which are widely used in their fields. To describe the relatively low frequency electromagnetic radiation in the macroscopic region, as a general rule, classical electrodynamics based on Maxwell's equations are used, and there are simplifications in the applications applied. For optical radiation (up to the X-ray range) optics (in particular, wave optics, when the dimensions of some parts of the optical system are close to the wavelengths; quantum optics, when the processes of absorption, emission and dispersion of photons are significant; Geometric optics is the limiting case of wave optics, when the radiation wavelength can be neglected.)

Gamma radiation is often the subject of nuclear physics, from other positions, medical and biological, we study the effect of electromagnetic radiation on radiology. There are also a number of areas, fundamental and applied, such as astrophysics, photochemistry, the biology of photosynthesis and visual perception, a series of areas of spectral analysis for which electromagnetic radiation (most often of a certain range ) and their interaction with matter play a key role. All these areas border and even intersect with the physics sections described above.

Some characteristics of electromagnetic waves from the point of view of oscillation theory and electrodynamic concepts:

  • the presence of three mutually perpendicular (empty) Vectors: wave vector, electric field vector E and magnetic field vector of intensity H.
  • Electromagnetic waves are transverse waves in which electric and magnetic field strength vectors oscillate perpendicularly to the direction of wave propagation, but differ significantly from water waves and the sound in which they can be transmitted from a source to a receiver. , even through a vacuum.

Biological effects of electromagnetic radiation

The effects of electromagnetic radiation on living things depend primarily on two main factors: the frequency of radiation and the type of radiation exposure (intensity of radiation, duration of exposure, exposed body part, etc.) that will determine the absorbed dose. The amount of radiation absorbed is measured in grays, a gray would correspond to the absorption of a joule of energy radiated by a kilogram of matter.

Regarding the frequency of radiation, it usually differentiates between ionizing and non-ionizing radiation.

Ionizing radiation

Ionizing radiations are those that have a frequency large enough to ionize the atoms or molecules of the exposed substances. This type of radiation is able to modify the chemical structure of the substances on which they affect and can produce long-term biological effects on living beings, an example would be the modification of the DNA of the cells, these DNA mutations can lead to cancer . X-rays and gamma radiation would be two examples of highly ionizing electromagnetic radiation.

Non-ionizing radiation

Non- ionizing radiations are those that do not have enough frequency to cause ionization of the exposed materials. As an example of non-ionizing radiation, microwave or radio waves can be mentioned. This type of radiation does not have enough energy to directly cause DNA mutations and, therefore, probably cannot initiate carcinogenesis but could be promoters. Today we talk about electromagnetic pollution to refer to the exposure of living beings or devices to an electromagnetic field and the effects of this exposure on health or fertility are discussed.

From the point of view of their health effects, non-ionizing radiation can be classified into three large groups:

  • Low frequency electromagnetic fields (ELF): range from 3 to 30,000 Hz).
  • Radio frequency and microwave fields: 30 kHz - 300 GHz range.
  • Optical radiation: from infrared light to ultraviolet light.

Only the biological effects of the first two groups will be discussed here, since the biological effects of the last group are developed in the corresponding articles (biological effects of infrared light and biological effects of ultraviolet light).

In the health effects of exposure to low frequency electromagnetic fields, a distinction must be made between the electric and magnetic fields. No health effects have been described as being exposed to electric fields of this frequency and, in addition, the penetrability is low and, for example, they cannot cross the walls. As for the effects of non-static magnetic fields, their effects on health are controversial. On the one hand there is a consensus among epidemiologists that children exposed to non-static magnetic fields have a higher risk of developing leukemia but, on the other hand, there is no widely accepted mechanism that explains how these fields can induce or promote cancer. The most important source of exposure is the generation, transport, distribution,

In 2002, the International Cancer Research Center published the evaluation of low frequency electromagnetic fields as possible carcinogens. His conclusions were:

  • Extremely low frequency magnetic fields are possible carcinogens in humans (Group 2B).
  • Extremely low frequency electric fields cannot be considered carcinogenic in humans (Group 3).
  • Static magnetic and electric fields can also not be considered carcinogenic in humans (Group 3).
  • The former were classified as possible carcinogens due to well-founded suspicions that are associated with a possible increase in the risk of childhood leukemia.

As regards the electromagnetic fields of radiofrequency and microwaves (30 kHz - 300 GHz), the most frequent source of exposure for the general population is mobile phones and their distribution towers. Its effects on health can be of two types:

  • Thermal: elevation of the central body temperature.
  • Athermal: fundamentally, cancer. It is a controversial effect.

Like the extremely low frequency magnetic fields, there is evidence from epidemiological studies that point to a moderate increase in cancer risk for subjects who have used a mobile phone for more than 10 years (but weakly supported by long-term animal experiments and in vitro research), but the evidence is not yet strong enough to convince the scientific community and the authorities that immediate action should be taken.

In 2011, the International Cancer Research Center brought together the world's leading experts on the subject to evaluate the possible carcinogenic effect of radiofrequency and microwave radiation (30 kHz - 300 GHz). According to the conclusions of the group of experts, the Center classified this type of radiation also within Group 2B (possible carcinogens in humans). It is not claimed that the exposure is carcinogenic, but it is not ruled out that it is.

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Last review: August 29, 2019