Radiation

Symbol indicating presence of ionizing radiation.

The phenomenon of radiation is the propagation of energy in the form of electromagnetic waves or subatomic particles through a vacuum or a material medium. There are different forms of radiation with different properties and effects.

Introduction

The radiation propagated in the form of electromagnetic waves (UV rays, gamma rays, X-rays, etc.) is called electromagnetic radiation, while the so-called corpuscular radiation is the radiation transmitted in the form of particles subatomic particles (α particles, β particles, neutrons, etc.) that move at high speed, with appreciable energy transport.

If the radiation carries enough energy to cause ionization in the medium it passes through, it is said to be ionizing radiation. Otherwise, there is talk of non-ionizing radiation. The ionizing or non-ionizing nature of radiation is independent of its corpuscular or wave nature.

Ionizing radiations include X-rays, γ-rays, α-particles and part of the spectrum of UV radiation, among others. On the other hand, radiation such as visible light rays, radio, TV or mobile phone waves are some examples of non-ionizing radiation.

Radioactive Elements

Some chemicals are made up of chemical elements whose atomic nuclei are unstable. As a consequence of this instability, its atoms emit subatomic particles intermittently and randomly. In general, substances that have an excess of protons or neutrons are radioactive. When the number of neutrons differs from the number of protons, it becomes more difficult for the strong nuclear force due to the pion exchange effect to hold them together. Eventually the imbalance is corrected by the release of excess neutrons or protons, in the form of α particles that are really helium nuclei, β particles that can be electrons or positrons. These emissions lead to two types of radioactivity:

• Radiation α, which lightens the atomic nuclei in 4 basic units, and changes the atomic number in two units.
• Radiation β, which does not change the mass of the nucleus, since it implies the conversion of a proton into a neutron or vice versa, and changes the atomic number in a single unit (positive or negative, according to the particle issued is an electron or a positron).

There is also a third type of radiation in which high-frequency photons are simply emitted, called γ radiation. In this type of radiation, what happens is that the nucleus goes from an excited state of higher energy to another of lower energy, which can continue to be unstable and give rise to the emission of more radiation of the α, β or γ type. γ radiation is a type of electromagnetic radiation that is very penetrating because photons have no electrical charge.Citation error: Cite error: open code exists <ref> without its closing code </ref> (effects are reduced if the same number of Siéverts accumulates over a longer period):

Symbol indicating presence of ionizing radiation.

Symptoms in humans due to accumulated radiation over a year, in millisieverts (1 Sv=1000 mSv):

• 2.5 mSv: Global average radiation.
• 5.5 - 10.2 mSv: Average natural values in Guarapari (Brazil) and in Ramsar (Iran). No harmful effects.
• 6.9 mSv: Scanner CT.

• 50 - 250 mSv: Limit for prevention and emergency workers, respectively.

Linear Energy Transfer (LET)

Linear energy transfer or LET (Linear Energy Transfer) is a measure that indicates the amount of energy "deposited" by radiation in the continuum that is traversed by it. Technically it is expressed as the energy transferred per unit length. The value of the LET depends both on the type of radiation and on the characteristics of the material medium that it passes through.

Radiation beam and its penetration capacity

The LAW is directly related to two very important properties in radiation analysis: the penetrating capacity and the amount of "dose" who deposit:

1. A high-LET radiation beam (e. g. α particles will deposit all your energy in a small region of the medium, so you will lose your energy quickly and will not be able to go through considerable thicknesses. For the same reason it will leave a high dose in the material.
2. A low-LET radiation beam (e. g. electromagnetic radiation and γ-radiation gamma-) will deposit your energy slowly, so before you have lost all your energy you will be able to cross a large thickness of material. That's why you'll leave a low dose in the middle you go through.

This explains why we can shield ourselves from α particles with a simple layer of air, yet a great thickness of lead or other heavy metal is necessary to shield us from gamma rays.

Biologically, these measures are important, since various radiations can cause damage to health depending on the intensity of the radiation or the LET to which the human body is exposed. It is also important to note that the doses do not only depend on the LET.