1. Federal Ministry for the Environment, Nature conservation, building and nuclear safety. Radiological protection, medicine. Available at: http://www.bmub.bund.de/themen/atomenergie-strahlenschutz/strahlenschutz/medizin/. Published 2017. In German. Accessed 14 May, 2017.
2. German Federal Office for Radiation Protection. X-ray-diagnostics: frequency and radiation exposure. Available at: https://www.bfs.de/EN/topics/ion/medicine/diagnostics/x-rays/frequency-exposure.html. Published 2017. Accessed 14 May, 2017.
3. German Federal Office for Radiation Protection FORP. Environmental radioactivity and radiation exposure: annual report 2014. Available at: http://nbn-resolving.de/urn:nbn:de:0221-2016091514109. Published 2016. In German. Accessed 14 May, 2017.
4. United States Nuclear Regulatory Commission. Protecting people and the environment. §20.1003 definitions. https://www.nrc.gov/reading-rm/doc-collections/cfr/part020/part020-1003.html. Accessed 21 January, 2018.
5. The Council of the European Union. Council Directive 2013/59/EURATOM of 5 December 2013 laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom und 2003/122/Euratom. Available at: http://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32012L0059&from=EN. Accessed 14 May, 2017.