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Ionizing Radiation

Ionizing radiation

An ionizing radiation is that radiation formed by photons or particles that, when interacting with matter, produce ions, whether they do so directly or indirectly.

Examples of ionizing electromagnetic radiation:

  1. The highest energy ultraviolet rays.
  2. X-rays and gamma rays

Examples of corpuscular ionizing radiation:

  1. Alpha radioactivity.
  2. The beta decay.

Visible light and infrared rays are not ionizing radiation, nor are radio radio waves.

These radiations were discovered by Wilhelm Conrad Röntgen in 1895. Since then, they have been used in medical and industrial applications. Despite the variety of uses, ionizing radiation presents a health risk if the correct measures are not taken against unwanted exposure. Exposure to ionizing radiation causes damage to living tissue and can cause mutations, acute radiation sickness, cancer, and death.

In the field of nuclear medicine, the best known application of X-ray devices, or the use of radiation sources in the medical field, both in diagnosis (scintigraphy) and in treatment (radiation therapy in oncology, for example) by the use of sources or particle accelerators.

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

What is the origin of ionizing radiation?

Ionizing radiation can have a natural or artificial origin. Naturally, some radioactive substances can emit radiation spontaneously. On the other hand, there are artificial generators, such as X-ray generators and particle accelerators.

Some elements are more suitable than others to produce this type of reaction. This is the case of uranium-235, with a tendency to absorb any neutron that collides with it. When this occurs, uranium-235 increases in 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, enough energy is released  to generate more reactions. Then,  a sequence of chain reactions occurs. These divisions of the nucleus of atoms are called nuclear fission and generate significant amounts of radioactivity and energy.

In reality, these nuclear fission reactions are what are generated in nuclear reactors so that the rest of the nuclear power plant can convert this energy into electricity.

What is radiobiology?

Radiobiology is the interdisciplinary field of science that encompasses the biological consequences of ionizing and non-ionizing radiation across the spectrum of electromagnetic waves. This field includes radioactivity (alpha, beta, and gamma), X-rays, ultraviolet rays, visible light, microwaves, and radio waves.

In addition, radiobiology studies low-frequency radiation (as used in alternating electrical transmission, ultrasound ( heat) thermal radiation, and related modalities. The area was founded by Louis Harold Gray.

In summary, radiobiology studies how ionizing radiation interacts with living matter and the effects it produces.

What are the physical effects of ionizing radiation?

We can classify the physical effects of ionizing radiation into:

  • Nuclear effects
  • Chemical effects
  • Electrical Effects

Nuclear effects

Neutron (subatomic particles), alpha rays, and extremely energetic gamma rays (> 20 MeV) can cause nuclear transmutation. The relevant mechanisms are neutron activation and photo-decay.

A fairly large number of transmutations can change macroscopic properties and cause targets to become radioactive, even after the original source is removed.

Chemical effects

Ionizing radiation that interacts with molecules can lead to:

  • Radiolysis (breakage of chemical bonds)
  • Highly reactive free radical formation. These free radicals, which have an unpaired electron, can chemically react with neighboring elements, subtracting one electron from them, even after the original radiation has stopped.
  • Destruction of crystal lattices, making them amorphous.
  • Accelerating chemical reactions, such as polymerization, that help 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 monoatomic fluids that do not have chemical bonds to break and that do not interfere with the crystal lattice.

In contrast, simple biatomic compounds with highly negative enthalpy, such as hydrofluoric acid, will rapidly and spontaneously reform after ionization.

Electrical Effects

The ionization of materials temporarily increases their conductivity, affecting the  electronics of the atoms . This is a particular hazard in semiconductor microelectronics with the risk of delayed currents introducing operating errors. Semiconductor microeletronics is used in electronic equipment.

In the case of high flows, the device itself is permanently damaged. Proton radiation existing in space can also significantly change the state of digital circuits.

Devices intended for high radiation environments can be manufactured to resist such effects through design, material selection and manufacturing methods. These devices are commonly used in space equipment (extra-atmospheric) and for the nuclear industry.

In reality, the more complex circuits used by the software manage to compensate for the errors due to irradiation.

What effects does radiation have on health?

Ionizing radiation can affect biological tissues and, therefore, health.

The damages it can cause to biological tissues are of various types and are divided into:

  • Deterministic somatic damage. Deterministic effects involve high doses of radiation to large portions of the body.
  • Stochastic somatic damage. Non-deterministic effects occur at low levels of radiation exposure. In this case, the damage is statistical. That is, it is possible to predict the proportion of a given population of exposed people that will be affected, but impossible to know how it will affect each person individually.
  • Stochastic genetic damage. These damages describe the inherited genotypic alterations resulting from mutations in the germ cell genes or chromosomes.

Somatic damage refers to damage that has occurred in the tissues of the irradiated individual. On the other hand, genetic damage refers to damage that will affect future generations. 

Current anti-pollution regulations set strict limits on individual exposure, which also involve exposure to common building materials such as tuff (which releases radon fumes).

    Effects of alpha radiation on health

    Alpha radiation has a low penetrating power, therefore it is easily stopped by the superficial layer of dead skin cells. In this sense, the skin performs a function of  radiological protection,  so it is not dangerous for humans in cases of external radiation.

    Instead, alpha radiation becomes dangerous in situations where the radioactive source is inhaled or ingested (internal radiation) because in this case it can directly damage radiosensitive tissues.

    Effects of gamma radiation on health

    On the other hand, gamma radiation (photons), which has a very high penetrating 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.

    What are the sources of ionizing radiation?

    Natural sources:

    Artificial sources:

    • Artificial radionuclides.
    • Nuclear reactors.
    • Particle accelerators (generate charged particle fluxes as well as bremsstrahlung photon radiation).
      • 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 disintegration 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 radiation from a radioactive source can vary significantly over time.

    References

    Biological effects of radiation - Dosimetry  (es - pdf)

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    Published: November 28, 2019
    Last review: March 21, 2020