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Ionizing Radiation

Ionizing Radiation

An ionizing radiation is that radiation formed by photons or particles that interact with matter produce ions, whether they do so directly or indirectly. Examples of ionizing electromagnetic radiation are the highest energy ultraviolet rays, X-rays and gamma rays; while as examples of corpuscular ionizing radiation, alpha radioactivity and beta decay can be used. Ionizing radiation is not visible light, nor infrared rays, nor radio radio waves.

They are used, since their discovery by Wilhelm Conrad Röntgen in 1895, in medical and industrial applications, and is the best known application of X-ray devices, or the use of radiation sources in the medical field, both in diagnosis (scintigraphy) as in treatment (radiation therapy in oncology, for example) through the use of sources or particle accelerators.

Ionizing radiation is invisible and not directly detectable by human senses, so instruments are needed to detect radiation, such as Geiger counters, to detect it. However, it can cause the emission of visible light immediately after interaction with matter, such as Cherenkov radiation and radioluminescence.

Ionizing radiation is used in a variety of fields, including nuclear medicine, research, manufacturing and construction, but it poses a health risk if the right measures against unwanted exposure are not taken. Exposure to ionizing radiation causes damage to living tissues and can cause mutations, acute radiation diseases, cancer and death.

Origin of ionizing radiation

Ionizing radiation can come from radioactive substances, which emit these radiations spontaneously, or from artificial generators, such as X-ray generators and particle accelerators. Ionizing radiation interacts with living matter, producing various effects. The study of this interaction and its effects is responsible for radiobiology.

Some elements are more suitable than others to produce such reactions. This is the case of uranium-235, with a tendency to absorb any neutron that collides with it. When this occurs, uranium-235 gains weight, becomes more unstable and ends up breaking into several fragments, releasing other neutrons. If these neutrons are absorbed, in turn, by other uranium-235 atoms a sequence of chain reactions occurs, which generates significant amounts of radioactivity and energy.

Physical effects of ionizing radiation

We can classify the physical effects of ionizing radiation in:

  • Nuclear effects
  • Chemical effects
  • Electrical effects

Nuclear effects

Neutrons, alpha rays and extremely energetic gamma rays (> 20 MeV) can cause nuclear transmutation. The relevant mechanisms are neutron activation and photointegration. A fairly large number of transmutations can change the macroscopic properties and cause the targets to become radioactive, even after the original source is removed.

Chemical effects

Ionizing radiation that interacts with molecules can lead to:

  • radiolysis (rupture of chemical bonds)
  • formation of highly reactive free radicals. These free radicals, which have an unpaired electron, can react chemically with neighboring elements, subtracting an electron from them, even after the original radiation has stopped.
  • destruction of the crystalline networks, making them amorphous.
  • acceleration of chemical reactions, such as polymerization, which helps achieve the activation energy required for the reaction.

Instead, there are some elements that are immune to the chemical effects of ionizing radiation, such as monatomic fluids (e.g., sodium melt) that have no chemical bonds to break and that does not interfere with the crystal lattice. In contrast, simple biatomic compounds with enthalpy of very negative formation, such as hydrofluoric acid, will rapidly and spontaneously reform after ionization.

Electrical effects

The ionization of materials temporarily increases its conductivity. This is a particular danger in semiconductor microelectronics, used in electronic equipment, with the risk of delayed currents that introduce operating errors or, in the case of high flows, the device itself is permanently damaged. Proton radiation in space can also significantly change the state of digital circuits.

Devices intended for high radiation environments, such as space equipment (extra-atmospheric) and for the nuclear industry, can be manufactured to withstand such effects through design, material selection and manufacturing methods. In reality, the more complex circuits that use the software compensate for errors due to irradiation.

Effects of ionizing radiation on health

In cases where ionizing radiation affects biological tissues, it can cause damage to health. In fact, alpha radiation has a low penetration power, therefore, it is easily stopped by the superficial layer of dead skin cells, so it is not dangerous for humans in cases of external radiation. Instead, it becomes dangerous in situations where the radioactive source is inhaled or ingested (internal radiation) because in this case it can directly damage radiosensitive tissues.

On the other hand, gamma radiation (photons), which has a very high penetration power, can be dangerous for living beings even in situations of external radiation. The amount of radiation absorbed by a body is called the absorbed dose and is measured in gray.

The damages that ionizing radiation can cause to biological tissues are of various types and are divided into:

  • deterministic somatic damage
  • stochastic somatic damage
    • stochastic genetic damage

The National Institute of Health estimates that in Italy there are between 1,500 and 9,000 deaths per year due to lung cancer due to exposure to natural sources of radioactivity. Current regulations against pollution establish strict limits on individual exposure, which also involve exposure to common building materials such as tuff (which releases radon vapors).

Sources of ionizing radiation

Natural sources of ionizing radiation:

  • Spontaneous radioactive decay of radionuclides.
  • thermonuclear reactions, like the sun.
  • Induced nuclear reactions as a result of the entry into the nucleus of elementary particles of high energy or nuclear fusion.
  • Cosmic rays.

Artificial sources of ionizing radiation:

  • Artificial radionuclides
  • Nuclear reactors.
  • Particle accelerators (generate charged particle flows, as well as radiation from bremsstrahlung photons).
    • X-ray apparatus as a type of accelerator, the brake generates X-rays.

Induced radioactivity

As a result of irradiation and the corresponding induced nuclear reaction, many stable atoms become unstable isotopes. As a result of such irradiation, a stable substance becomes radioactive and the type of secondary ionizing radiation will differ from the initial exposure. This effect is more pronounced after neutron irradiation.

The chain of nuclear transformations

In the process of nuclear decay or synthesis, new nuclides arise, which can also be unstable. The result is a chain of nuclear transformations. Each transformation has its own probability and its own set of ionizing radiation. As a result, the intensity and nature of the radiation from a radioactive source can vary significantly over time.

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Last review: November 28, 2019