Ionizing and non-ionizing radiation


    In terms of the hazard they pose to human health, radiation fall into 2 categories: non-ionizing and ionizing.
   Electromagnetic radiation such as light, ultraviolet and infrared radiation, radio waves, microwaves and ultrasounds, belongs to the first category.
    When radiation strikes an atom, transfers some energy to it. If the energy transferred by radiation is high enough, ionization is produced, being the process of removing an electron from the atom and leaving behind two charged particles: an electron and a positive ion. The presence of large numbers of such charged particles can create damages in living tissues.

     The radiation which can transfer enough energy to do this kind of damages, are called ionizing radiation; those with a lower level of energy, are called non-ionizing radiation. While some types of non-ionizing radiation can be harmful in high doses, the ionizing ones are usually much more dangerous.


Radioactive decay

   Radioactivity is the spontaneous disintegration ability of an atom. In this way, a new atom is formed by releasing of a radiation.
   An atom can emit 3 types of radioactive radiation: positive alpha radiation, negative beta radiation and gamma radiation electrically neutral. During the radioactive decay, an element does not emit all types of radiation at the same time.
     In nature, most of the nuclides are stable, but there are certain nuclides, existing in nature, or man-made, that have the property called radioactivity. These ones are called radionuclides.

     The decay is a random process. The moment when a particular nucleus will decay, can’t be provided, but the average rate of the nucleus decay and the type of radiation emitted, are the characteristics of the radionuclide.


Measurement of radioactivity

    The amount of radiation emitted by a radioactive element is measured in units of “activity” called Becquerels (Bq). 1 Bq equals one disintegration per second. For example, the average activity of human body is about 120 Bq per kilogram. 1 Bq is a very low level of radioactivity, so often, the values are expressed in kBq (thousands of Bq), or in MBq (millions of Bq), or in GBq (billions of Bq).
     Tolerated unit of activity is Ci (Curie):   1 Ci = 3,7 x 10¹º dis/s = 3,7 x 10¹º Bq
    One unit of measurement related to the decay rate of a radionuclide, is the physical half-life (T½ or Tf), which is also a constant characteristic of a radionuclide. This is the average time it takes for the one-half of the atoms from a sample of the radionuclide, to disintegrate.

Types of ionizing radiation and their penetration power

Different sources emit different types of ionizing radiation:
  • Alpha radiation (ά), actually Helium atoms, interacts with many atoms on a very short distance. They give rise to ions and they burn all their own energy on that short distance. Most alpha particles will consume their all energy at the crossing of a simple sheet of paper. The main health effect linked to alpha particles occurs when alpha-emitting materials are ingested or inhaled and the energy of alpha particles affects the internal tissues such as the lungs.
  • Beta radiation (β), consists of electrons – negatively charged light particles. These particles moves in the air on a greater distance than alpha particles and can pass through a paper sheet, but can’t penetrate the skin of human body. Health effects associated to beta particles mainly occur when beta-emitting materials are ingested or inhaled.
  • Gamma radiation (γ), takes the form of electromagnetic waves or photons emitted from the nucleus of an atom. This radiation can completely cross the human body and can be stopped only by a concrete wall or a lead plate of 15 cm minimum thickness. Gamma radiation is stopped by water, concrete and, in particular, by the dense materials such as lead, usually used for protection against exposure to such radiation. Health effects associated to gamma particles are primarily manifested when gamma-emitting materials are outside of the human body.
  • X-rays are low energy gamma radiation. If the human body, this radiation can penetrate the muscle tissues, but can’t penetrate the bones, hence their utility in medicine (X-rays investigation).

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