The Council of the European Union adopted Directive 2013/59/Euratom on 17 January 2014.
The provisions of the Directive applicable to aircrew and space crew were implemented in the UK as the Air Navigation (Cosmic Radiation: Protection of Air Crew and Space Crew and Consequential Amendments) Order 2019, which came into force on 7 August 2019.
Radiation is the transfer of energy from a source. It may be in the form of electromagnetic radiation such as x-rays and gamma rays. It may also be in the form of particles such as neutrons and protons. Cosmic radiation is the collective term for the radiation which comes from the Sun (the solar component) and from the galaxies of the Universe (the galactic component). Cosmic radiation is ionising, i.e. it can displace charged particles from atoms. This can lead to the disruption of molecules in living cells. Processes in the cell repair most of this damage. Cosmic radiation consists of a complex mixture of radiations and their interactions in the atmosphere are similarly complex. Nevertheless, the Earth's atmosphere substantially shields the Earth from cosmic radiation, and doses of cosmic radiation are greater with increasing altitude.
Cosmic radiation particles may be electrically charged and so may be deflected by the Earth's magnetic field, it is for this reason that doses of cosmic radiation are greater at higher latitudes towards the Earth's magnetic poles. The deflection of cosmic radiation particles is least for higher energy particles and for particles of all energies travelling parallel to the magnetic field lines. The deflection is greatest for lower energy particles such that apart from exceptional solar events, the solar component of cosmic radiation is of no direct concern. The output of radiation from the Sun varies in an approximate 11-year cycle. At times of maximum solar output, associated with increasing numbers of sunspots, the magnetic field embedded within the Sun's radiation serves to deflect more of the galactic cosmic radiation component away from Earth. For this reason doses are about 20% lower than the mean value during maximum solar activity and about 20 % higher during solar minimum. Mainly, but not exclusively, during solar maximum there is a small probability of a solar flare giving rise to exceptionally high numbers of energetic particles such that there are increased levels of cosmic radiation at aircraft altitudes.
All living things on Earth are exposed to a background level of radiation from naturally occurring substances both on Earth and in space (see the section below called Doses from cosmic radiation).
Additionally, there may be further exposure from man-made sources such as medical x-rays. There is direct evidence that high levels of radiation are harmful to humans. It is also believed that lower levels carry a risk which is in proportion to the dose. The risks from radiation exposure are detailed in the International Commission on Radiological Protection risk estimates .