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Defining radiation

This illustration describes the electromagnetic spectrum which is divided into non-ionizing and ionizing electromagnetic fields depending on the energy the radiation contains. The fields with the lowest energy are the extremely low frequency (ELF) fields to the left with 10-1 000 Hz, and a long wavelength of 10 000 km and more. These fields are typically arising from electric powerlines. Increasing the energy in the fields the next part in the spectrum is the radiofrequency electromagnetic fields. They are used for broadcasting, mobile phone technology and navigation such as radars and has frequencies ranging from 10 000 000 – 10 000 000 000 000 Hz and wavelengths from 1 km to 1 mm. These fields contain much higher energy than the ELF fields, but even higher energy are in the infrared, visual light and ultraviolet spectrum of the fields. Approximately when the electromagnetic waves are 10-7 m and has a frequency of 100 000 000 000 000 000 Hz the radiation waves themselves contain enough energy to ionize molecules. This part of the spectrum is called the ionizing electromagnetic fields and the fields are called X-rays which are used in medicine and GAMMA-rays which are known from radioactive sources. The electromagnetic Spectrum. Energy per radiation beam increases from left to right, with the highest energy containing the ionizing part of the Spectrum (E =extremely, L=low, F=frequency, R=radio, H =high, UV =ultraviolet, MRI=magnetic resonance imaging, GSM=global system for mobile, 3G=3rd generation).


Radiation is divided into non-ionizing and ionizing electromagnetic fields and is a way of transferring energy. To produce radiation it requires a source which emits the radiation. The radiation will then disperse in the medium with the highest concentrations close to the source, and diminishing the farther away from the source you are. This dispersion leads to reduced exposure when the distance from the radiation source increases. This is often calculated roughly as Exposure = 1/distance2.

figure showing source of radiation and distance from source and the reduced strength of radiation as is gets further from the source ©University of Bergen/Arjun Ahluwalia

Objects hit by radiation will absorb some of it. The amount of absorption depends on the type and magnitude of the radiation, the time-span of exposure and the tissue exposed, as different tissues will absorb different amounts of energy. This can be illustrated by the differences in the absorption of solar energy between a metal- or wooden bench in the sun; the bench made of metal will become much warmer than the wooden bench, even though the amount of radiation energy received is the same.

Sign for ionizing radiation on a hospital door in Tanzania_3883.JPG Sign for ionizing radiation on a hospital door in Tanzania. © G. Tjalvin

Ionizing radiation

This type of radiation possesses enough energy to cause ionization of molecules or atoms, which can cause active and potentially damaging processes in cells and living things. The ionizing radiation may be described in different ways, one is by the term “Becquerel”. This describes the radioactive activity of the material defined as being the number of nucleous decays per second. More descriptive of the energy absorbed per amount of tissue is the term “Gray”, but even more descriptive is “Sievert” which also takes into account the radiated tissues ability to absorb the radiation.

Non-ionizing radiation (NIR):

The non-ionizing part of the electromagnetic spectrum does not have the ability to ionize molecules or atoms, but NIR can harm by other mechanisms, depending on the amount of the non-ionizing radiation and the time-span of exposure. It is descried as “Volt/m” for electric fields and “Tesla” for magnetic fields. These different values for electric and magnetic fields can be combined to give rise to the unit known as Specific Absorption Rate (SAR). This describes how much energy is absorbed by human tissue.

Legislation and associations

Legislation on issues related to radiation and health may differ from country to country. The International Atomic Energy Agency has published a report entitled “Agency Radiation protection and safety of radiation sources: International basic safety standards – Interim edition”, which is posted on the web pages of ILO:

The objective of this Safety Requirements publication is to establish guidelines for the protection of people and the environment from harmful effects of ionizing radiation and for ensuring the safe operation and management of ionizing radiation sources. This publication is intended for use by governmental authorities including regulatory bodies responsible for licensing facilities and activities; by organizations operating nuclear facilities, some mining and raw material processing facilities such as uranium mines, radioactive waste management facilities, and any other facilities producing or using radiation sources for industrial, research or medical purposes; by organizations transporting radioactive material; by organizations decommissioning facilities; and by staff and technical and scientific support organizations supporting such organizations and authorities.

There are also two other organisations which have published information that can be useful when discussing such topics:

a) The International Commission on Radiation Protection (ICRP)

ICRP is an independent, international organisation with more than two hundred volunteer members from approximately thirty countries across six continents. These members represent the leading scientists and policy makers in the field of radiological protection. ICRP is funded through a number of ongoing contributions from organisations with an interest in radiological protection. Since 1928, ICRP has developed, maintained, and elaborated the International System of Radiological Protection used world-wide as the common basis for radiological protection standards, legislation, guidelines, programmes, and practice The work of the International Commission on Radiological Protection (ICRP) helps to prevent cancer and other diseases and effects associated with exposure to ionizing radiation, and to protect the environment. ICRP has published more than one hundred reports on all aspects of radiological protection. Most address a particular area within radiological protection, but a handful of publications, the so-called fundamental recommendations, each describe the overall system of radiological protection. The International System of Radiological Protection has been developed by ICRP based on the current understanding of the science of ionizing radiation exposures and effects and value judgements. These value judgements take into account societal expectations, ethics, and experience gained in application of the system. You can find information from ICRP on their webpage ICRP

b) The International Commission on Non-Ionizing Radiation Protection (ICNIRP)

ICNIRP provides scientific advice and guidance on the health and environmental effects of non-ionizing radiation (NIR) to protect people and the environment from detrimental NIR exposure. ICNIRP is an independent non-profit scientific organization chartered in Germany. It was founded in 1992 by the International Radiation Protection Association to which it maintains close relations. The mission of ICNIRP is to screen and evaluate scientific knowledge and recent findings toward providing protection guidance on NIR. The commission produces reviews of the current scientific knowledge and guidelines summarizing its evaluation. ICNIRP provides its science-based advice free of charge. In the past, national authorities in more than 50 countries and multinational authorities such as the European Union have adopted the ICNIRP guidelines and translated them into their own regulatory framework on protection of the public and of workers from established adverse health effects caused by exposure to non-ionizing radiation. ICNIRP consists of a main commission of eight members, covering the fields of epidemiology, biology and medicine, physics and dosimetry and optical radiation. The members are scientists employed typically by universities or radiation protection agencies. They do not represent their country of origin, nor their institute and cannot be employed by commercial companies. ICNIRP is widely connected to a large community working on non-ionizing radiation protection around the world. You can find more information about ICNIRP on their web site

In addition, you might also find information of interest on web pages of the association International Radiation Protection Association (IRPA). IRPA was formed in 1965. The primary purpose of IRPA is to provide a medium whereby those engaged in radiation protection activities in all countries may communicate more readily with each other and through this process advance radiation protection in many parts of the world. It is a major task for IRPA to provide for and support international meetings for the discussion of radiation protection. The International Congresses of IRPA itself are the most important of these meetings. These have been held about every four years since 1966. You can read more about IRPA here

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Occupational Health in Developing Countries

University of Bergen