Editing Background radiation (section)

==Natural background radiation==
[[File:Atomic Testing Museum weather display cropped.jpg|thumb|The weather station outside of the [[Atomic Testing Museum]] on a hot summer day. Displayed background [[Gamma ray|gamma radiation]] level is 9.8&nbsp;[[μR/h]] (0.82&nbsp;mSv/a) This is very close to the world average background radiation of 0.87&nbsp;mSv/a from cosmic and terrestrial sources.]]
[[File:Cloud chambers played an important role of particle detectors.jpg |thumb|upright|[[Cloud chamber]]s used by early researchers first detected cosmic rays and other background radiation.  They can be used to visualize the background radiation]]
Radioactive material is found throughout nature. Detectable amounts occur naturally in [[soil]], rocks, water, air, and vegetation, from which it is inhaled and ingested into the body. In addition to this ''internal exposure'', humans also receive ''external exposure'' from radioactive materials that remain outside the body and from cosmic radiation from space. The worldwide average natural [[effective radiation dose|dose]] to humans is about {{convert|2.4|mSv|mrem|abbr=on|lk=on}} per year.<ref name=UNSCEAR2008 /> This is four times the worldwide average artificial radiation exposure, which in 2008 amounted to about {{convert|0.6|mSv|mrem|lk=on}} per year. In some developed countries, like the US and Japan, artificial exposure is, on average, greater than the natural exposure, due to greater access to [[medical imaging]]. In Europe, average natural background exposure by country ranges from under {{cvt|2|mSv|mrem}} annually in the United Kingdom to more than {{cvt|7|mSv|mrem}} annually for some groups of people in Finland.<ref name=RadMapEurope>{{cite web|url=http://www.world-nuclear.org/info/Safety-and-Security/Radiation-and-Health/Naturally-Occurring-Radioactive-Materials-NORM/|title=Naturally-Occurring Radioactive Materials (NORM)|date=March 2019|website=World Nuclear Association|access-date=26 August 2014|archive-date=20 January 2016|archive-url=https://web.archive.org/web/20160120074033/http://www.world-nuclear.org/info/Safety-and-Security/Radiation-and-Health/Naturally-Occurring-Radioactive-Materials-NORM/|url-status=dead}}</ref>

The [[International Atomic Energy Agency]] states:
:"Exposure to radiation from natural sources is an inescapable feature of everyday life in both working and public environments. This exposure is in most cases of little or no concern to society, but in certain situations the introduction of health protection measures needs to be considered, for example when working with uranium and thorium ores and other Naturally Occurring Radioactive Material ([[NORM]]). These situations have become the focus of greater attention by the Agency in recent years."<ref>{{cite web |url = http://www-ns.iaea.org/tech-areas/rw-ppss/exposure-to-natural-radiation.asp?s=3 |publisher = IAEA |website = Nuclear Safety & Security |title = Exposure to radiation from natural sources |archive-url = https://web.archive.org/web/20160209112421/http://www-ns.iaea.org/tech-areas/rw-ppss/exposure-to-natural-radiation.asp?s=3 |archive-date = 9 February 2016 |access-date = 4 January 2016 |url-status = live }}</ref>

===Terrestrial sources===
{{Main|Environmental radioactivity}}
'''Terrestrial background radiation''', for the purpose of the table above, only includes sources that remain external to the body. The major [[radionuclide]]s of concern are [[potassium]], [[uranium]] and [[thorium]] and their decay products, some of which, like [[radium]] and [[radon]] are intensely radioactive but occur in low concentrations. Most of these sources have been decreasing, due to [[radioactive decay]] since the formation of the Earth, because there is no significant amount currently transported to the Earth. Thus, the present activity on Earth from [[uranium-238]] is only half as much as it originally was because of its 4.5&nbsp;[[1000000000 (number)|billion]] year half-life, and [[potassium-40]] (half-life 1.25 billion years) is only at about 8% of original activity. But during the time that humans have existed the amount of radiation has decreased very little.

Many shorter half-life (and thus more intensely radioactive) isotopes have not decayed out of the terrestrial environment because of their on-going natural production. Examples of these are [[radium]]-226 (decay product of thorium-230 in decay chain of uranium-238) and [[radon-222]] (a decay product of [[radium]]-226 in said chain).

Thorium and uranium (and their daughters) primarily undergo [[alpha decay|alpha]] and [[beta decay]], and are not easily detectable. However, many of their [[daughter product]]s are strong gamma emitters. [[Thorium-232]] is detectable via a 239&nbsp;keV peak from [[lead-212]], 511, 583 and 2614&nbsp;keV from [[thallium-208]], and 911 and 969&nbsp;keV from [[actinium-228]]. Uranium-238 manifests as 609, 1120, and 1764&nbsp;keV peaks of bismuth-214 (''cf.'' the same peak for atmospheric radon). Potassium-40 is detectable directly via its 1461&nbsp;keV gamma peak.<ref name="DetNuc"/>

The level over the sea and other large bodies of water tends to be about a tenth of the terrestrial background. Conversely, coastal areas (and areas by the side of fresh water) may have an additional contribution from dispersed sediment.<ref name="DetNuc"/>

===Airborne sources===
The biggest source of natural background radiation is airborne [[radon]], a radioactive gas that emanates from the ground. Radon and its [[isotope]]s, parent [[radionuclide]]s, and [[decay product]]s all contribute to an average inhaled dose of 1.26&nbsp;[[Sievert#Common SI usage|mSv/a]] (millisievert [[wikt:per annum|per year]]). Radon is unevenly distributed and varies with weather, such that much higher doses apply to many areas of the world, where it represents a [[Health effects of radon|significant health hazard]]. Concentrations over 500 times the world average have been found inside buildings in Scandinavia, the United States, Iran, and the Czech Republic.<ref name="UNSCEAR2006E">{{cite book|author=United Nations Scientific Committee on the Effects of Atomic Radiation|title=Effects of Ionizing Radiation |date=2006 |publication-date=2008 |publisher=United Nations|location=New York|isbn=978-92-1-142263-4|volume=II|chapter=Annex E: Sources-to-effects assessment for radon in homes and workplaces|chapter-url=http://www.unscear.org/docs/reports/2006/09-81160_Report_Annex_E_2006_Web.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.unscear.org/docs/reports/2006/09-81160_Report_Annex_E_2006_Web.pdf |archive-date=2022-10-09 |url-status=live|access-date=2 December 2012}}</ref> Radon is a decay product of uranium, which is relatively common in the Earth's crust, but more concentrated in ore-bearing rocks scattered around the world. Radon seeps out of these [[ores]] into the atmosphere or into ground water or infiltrates into buildings. It can be inhaled into the lungs, along with its [[decay product]]s, where they will reside for a period of time after exposure.

Although radon is naturally occurring, exposure can be enhanced or diminished by human activity, notably house construction. A poorly sealed dwelling floor, or poor basement ventilation, in an otherwise well insulated house can result in the accumulation of radon within the dwelling, exposing its residents to high concentrations. The widespread construction of well insulated and sealed homes in the northern industrialized world has led to radon becoming the primary source of background radiation in some localities in northern North America and Europe.{{citation needed|date=December 2012}} Basement sealing and suction ventilation reduce exposure. Some building materials, for example [[lightweight concrete]] with [[alum shale]], [[phosphogypsum]] and Italian [[tuff]], may emanate radon if they contain [[radium]] and are porous to gas.<ref name=UNSCEAR2006E />

Radiation exposure from radon is indirect. Radon has a short half-life (4 days) and decays into other solid particulate [[Decay chain#Radium series|radium-series]] radioactive nuclides. These radioactive particles are inhaled and remain lodged in the lungs, causing continued exposure. Radon is thus assumed to be the second leading cause of [[lung cancer]] after [[tobacco smoking|smoking]], and accounts for 15,000 to 22,000 cancer deaths per year in the US alone.<ref>{{cite web| url = http://www.cancer.gov/cancertopics/factsheet/Risk/radon| title = Radon and Cancer: Questions and Answers – National Cancer Institute (USA)| date = 6 December 2011}}</ref>{{better source needed|date=December 2012}}<!--Radon may also dissolve in groundwater and be ingested, producing a dose to the stomach and the foetus. But this section is about air, inhalation only--> However, the discussion about the opposite experimental results is still going on.<ref>{{cite journal |last=Fornalski |first=K. W. |author2=Adams, R. |author3=Allison, W. |author4=Corrice, L. E. |author5=Cuttler, J. M. |author6=Davey, Ch. |author7=Dobrzyński, L. |author8=Esposito, V. J. |author9=Feinendegen, L. E. |author10=Gomez, L. S. |author11=Lewis, P. |author12=Mahn, J. |author13=Miller, M. L. |author14=Pennington, Ch. W. |author15=Sacks, B. |author16=Sutou, S. |author17=Welsh, J. S. |pmid=26223888 |title=The assumption of radon-induced cancer risk |year=2015 |journal=Cancer Causes & Control |doi=10.1007/s10552-015-0638-9 |issue=26 |volume=10 |pages=1517–18|s2cid=15952263 }}</ref>

About 100,000&nbsp;Bq/m<sup>3</sup> of radon was found in [[Health effects of radon#Accumulation in dwellings|Stanley Watras's]] basement in 1984.<ref>{{cite conference |url=http://wpb-radon.com/Radon_research_papers/1995%20Nashville,%20TN/1995_14_Indoor%20Radon%20Concentration%20Data--Geographic%20and%20Geologic%20Distribution,%20Captial%20District,%20NY.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://wpb-radon.com/Radon_research_papers/1995%20Nashville,%20TN/1995_14_Indoor%20Radon%20Concentration%20Data--Geographic%20and%20Geologic%20Distribution,%20Captial%20District,%20NY.pdf |archive-date=2022-10-09 |url-status=live |title=Indoor Radon Concentration Data: Its Geographic and Geologic Distribution, an Example from the Capital District, NY |first1=John J. |last1=Thomas |first2=Barbara R. |last2=Thomas |first3=Helen M. |last3=Overeynder |date= 27–30 September 1995  |conference=International Radon Symposium |conference-url=http://internationalradonsymposium.org/ |publisher=American Association of Radon Scientists and Technologists |location=Nashville, TN |access-date=2012-11-28}}</ref><ref>{{cite book|last1=Upfal |first1=Mark J. |last2=Johnson |first2=Christine |title=Occupational, industrial, and environmental toxicology|year=2003|publisher=Mosby|location=St Louis, Missouri|isbn=9780323013406|chapter-url=http://toxicology.ws/Greenberg/Chapter%2065%20-%20Residential%20Radon.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://toxicology.ws/Greenberg/Chapter%2065%20-%20Residential%20Radon.pdf |archive-date=2022-10-09 |url-status=live|edition=2nd|chapter=65 Residential Radon|editor1-first=Michael I. |editor1-last=Greenberg |editor2-first=Richard J. |editor2-last=Hamilton |editor3-first=Scott D. |editor3-last=Phillips |editor4-first=Gayla J. |editor4-last=McCluskey|access-date=28 November 2012}}</ref> He and his neighbours in [[Boyertown, Pennsylvania]], United States may hold the record for the most radioactive dwellings in the world. International radiation protection organizations estimate that a [[committed dose]] may be calculated by multiplying the [[equilibrium equivalent concentration]] (EEC) of radon by a factor of 8 to 9 {{sfrac|nSv·m<sup>3</sup>|Bq·h}} and the EEC of [[thoron]] by a factor of 40 {{sfrac|nSv·m<sup>3</sup>|Bq·h}}.<ref name=UNSCEAR2008 /><!-- The 8 is from ICRP, noted by UNSCEAR along with their own value of 9-->

Most of the atmospheric background is caused by radon and its decay products. The [[gamma spectroscopy|gamma spectrum]] shows prominent peaks at 609, 1120, and 1764&nbsp;[[keV]], belonging to [[bismuth-214]], a radon decay product. The atmospheric background varies greatly with wind direction and meteorological conditions. Radon also can be released from the ground in bursts and then form "radon clouds" capable of traveling tens of kilometers.<ref name="DetNuc">Gary W. Philips, David J. Nagel, Timothy Coffey – [http://large.stanford.edu/courses/2011/ph241/keller1/docs/phillips.pdf A Primer on the Detection of Nuclear and Radiological Weapons], Center for Technology and National Security Policy, National Defense University, May 2005</ref>

===Cosmic radiation===
{{Main|Cosmic ray}}
[[Image:Sievert-sigle.png|thumb|upright=1.3|Estimate of the maximum dose of radiation received at an altitude of 12 km 20 January 2005, following a violent solar flare. The doses are expressed in microsieverts per hour.]]
The Earth and all living things on it are constantly bombarded by radiation from outer space. This radiation primarily consists of positively charged ions from [[proton]]s to [[iron]] and larger [[atomic nucleus|nuclei]] derived from outside the [[Solar System]]. This radiation interacts with atoms in the atmosphere to create an [[air shower (physics)|air shower]] of secondary radiation, including [[X-ray]]s, [[muon]]s, [[proton]]s, [[alpha particle]]s, [[pion]]s, [[electron]]s, and [[neutron]]s. The immediate dose from cosmic radiation is largely from muons, neutrons, and electrons, and this dose varies in different parts of the world based largely on the [[geomagnetic field]] and altitude. For example, the city of [[Denver]] in the United States (at 1650 meters elevation) receives a cosmic ray dose roughly twice that of a location at sea level.<ref>{{cite web
 | url =http://www.units.miamioh.edu/ehso/radiationtraining/backgroundradiation/index.htm
 | title =Background Radiation & Other Sources of Exposure 
 | website =Radiation Safety Training
 | publisher =[[Miami University]]
 | access-date =30 September 2016
 }}</ref> This radiation is much more intense in the upper [[troposphere]], around 10&nbsp;km altitude, and is thus of particular concern for [[airline]] crews and frequent passengers, who spend many hours per year in this environment. During their flights airline crews typically get an additional occupational dose between {{cvt|2.2|mSv|mrem}} per year <ref>{{cite web|title=Radiation Exposure During Commercial Airline Flights|access-date=2011-03-17|url=http://www.hps.org/publicinformation/ate/faqs/commercialflights.html}}</ref> and 2.19 mSv/year,<ref>{{cite web|url=http://www.hps.org/publicinformation/ate/faqs/commercialflights.html|title=Radiation exposure during commercial airline flights|author=Health Physics Society|access-date=2013-01-24}}</ref> according to various studies.<ref>{{cite web
 | url =https://www.faa.gov/data_research/research/med_humanfacs/aeromedical/radiobiology/
 | title =Radiobiology Research Team
 | website =Federal Aviation Administration
 | access-date =23 January 2022}}</ref>

Similarly, cosmic rays cause higher background exposure in [[astronaut]]s than in humans on the surface of Earth. Astronauts in low [[orbit]]s, such as in the [[International Space Station]] or the [[Space Shuttle]], are partially shielded by the [[magnetic field]] of the Earth, but also suffer from the [[Van Allen radiation belt]] which accumulates cosmic rays and results from the Earth's magnetic field. Outside low Earth orbit, as experienced by the [[Apollo program|Apollo]] astronauts who traveled to the [[Moon]], this background radiation is much more intense, and represents a considerable obstacle to potential future long term human exploration of the [[moon landing|Moon]] or [[Human mission to Mars|Mars]].

Cosmic rays also cause [[Nuclear transmutation|elemental transmutation]] in the atmosphere, in which secondary radiation generated by the cosmic rays combines with [[atomic nuclei]] in the atmosphere to generate different [[nuclide]]s. Many so-called [[cosmogenic nuclide]]s can be produced, but probably the most notable is [[carbon-14]], which is produced by interactions with [[nitrogen]] atoms. These cosmogenic nuclides eventually reach the Earth's surface and can be incorporated into living organisms. The production of these nuclides varies slightly with short-term variations in solar cosmic ray flux, but is considered practically constant over long scales of thousands to millions of years. The constant production, incorporation into organisms and relatively short [[half-life]] of carbon-14 are the principles used in [[radiocarbon dating]] of ancient biological materials, such as wooden artifacts or human remains.

The cosmic radiation at sea level usually manifests as 511&nbsp;keV gamma rays from annihilation of [[positron]]s created by nuclear reactions of high energy particles and gamma rays. At higher altitudes there is also the contribution of continuous [[bremsstrahlung]] spectrum.<ref name="DetNuc"/>

===Food and water===
Two of the essential elements that make up the human body, namely potassium and carbon, have radioactive isotopes that add significantly to our background radiation dose. An average human contains about 17 milligrams of [[potassium-40]] (<sup>40</sup>K) and about 24 nanograms (10<sup>−9</sup>&nbsp;g) of [[carbon-14]] (<sup>14</sup>C),<ref>{{Cite web |title=Radioactive Human Body |url=https://sciencedemonstrations.fas.harvard.edu/presentations/radioactive-human-body |access-date=2022-10-12 |website=sciencedemonstrations.fas.harvard.edu |language=en}}</ref> (half-life 5,730 years). Excluding internal contamination by external radioactive material, these two are the largest components of internal radiation exposure from biologically functional components of the human body. About 4,000 nuclei of <sup>40</sup>K <ref>{{cite web |url = http://sciencedemonstrations.fas.harvard.edu/icb/icb.do?keyword=k16940&pageid=icb.page102829&pageContentId=icb.pagecontent270775&state=maximize&view=view.do&viewParam_name=indepth.html#a_icb_pagecontent270775 |title = Radioactive human body&nbsp;– Harvard University Natural Science Lecture Demonstrations |archive-url=https://web.archive.org/web/20150612194741/http://sciencedemonstrations.fas.harvard.edu/icb/icb.do?keyword=k16940&pageid=icb.page102829&pageContentId=icb.pagecontent270775&state=maximize&view=view.do&viewParam_name=indepth.html#a_icb_pagecontent270775 |archive-date=12 June 2015 |url-status=dead}}</ref> decay per second, and a similar number of <sup>14</sup>C. The energy of [[beta particle]]s produced by <sup>40</sup>K is about 10 times that from the beta particles from <sup>14</sup>C decay.

<sup>14</sup>C is present in the human body at a level of about 3700 Bq (0.1&nbsp;μCi) with a [[biological half-life]] of 40 days.<ref>{{cite web|url = http://www.ead.anl.gov/pub/doc/carbon14.pdf|title = Carbon 14|work = Human Health Fact Sheet|date = August 2005|publisher = Argonne National Lab|archive-url = https://web.archive.org/web/20080227103725/http://www.ead.anl.gov/pub/doc/carbon14.pdf|archive-date = 27 February 2008|access-date = 4 April 2011|url-status = live}}</ref> This means there are about 3700 beta particles per second produced by the decay of <sup>14</sup>C. However, a <sup>14</sup>C atom is in the genetic information of about half the cells, while potassium is not a component of [[DNA]]. The decay of a <sup>14</sup>C atom inside DNA in one person happens about 50 times per second, changing a carbon atom to one of [[nitrogen]].<ref>{{cite book |last=Asimov |first=Isaac |author-link=Isaac Asimov |title=Only A Trillion |orig-year=1957 |edition=Revised and updated |year=1976 |publisher=ACE books |location=New York |pages=37–39 |chapter=The Explosions Within Us |isbn= 978-1-157-09468-5 }}</ref>

The global average internal dose from radionuclides other than radon and its decay products is 0.29&nbsp;mSv/a, of which 0.17&nbsp;mSv/a comes from <sup>40</sup>K, 0.12&nbsp;mSv/a comes from the uranium and thorium series, and 12&nbsp;μSv/a comes from <sup>14</sup>C.<ref name=UNSCEAR2008 />

===Areas with high natural background radiation===
Some areas have greater dosage than the country-wide averages.<ref>[http://www.taishitsu.or.jp/radiation/index-e.html Annual terrestrial radiation doses in the world] {{webarchive|url=https://web.archive.org/web/20070623020422/http://www.taishitsu.or.jp/radiation/index-e.html |date=23 June 2007 }}</ref> In the world in general, exceptionally high natural background locales include [[Ramsar, Mazandaran|Ramsar]] in Iran, [[Guarapari]] in Brazil, [[Karunagappalli]] in India,<ref>{{cite journal |pmid=10564957 |year=1999 |last1=Nair |first1=MK |last2=Nambi |first2=KS |last3=Amma |first3=NS |last4=Gangadharan |first4=P |last5= Jayalekshmi |first5= P |last6=Jayadevan |first6=S |last7=Cherian |first7=V |last8=Reghuram |first8=KN |title=Population study in the high natural background radiation area in Kerala, India |volume=152 |issue=6 Suppl |pages=S145–48 |journal=Radiation Research |doi=10.2307/3580134|bibcode=1999RadR..152S.145N |jstor=3580134 }}</ref> [[Arkaroola]] in Australia<ref>{{cite web|url=http://www.abc.net.au/catalyst/stories/s692473.htm|title=Extreme Slime|work=Catalyst|publisher=ABC|date=3 October 2002|archive-url=https://web.archive.org/web/20030415055740/http://www.abc.net.au/catalyst/stories/s692473.htm|archive-date=15 April 2003|access-date=2 March 2009|url-status=live}}</ref> and [[Yangjiang]] in China.<ref>{{cite journal| last =Zhang| first =SP| title =Mechanism study of adaptive response in high background radiation area of Yangjiang in China| pmid=21092626 | volume=44| issue =9| year=2010| journal=Zhonghua Yu Fang Yi Xue Za Zhi| pages=815–19}}</ref>

The highest level of purely natural radiation ever recorded on the Earth's surface was 90&nbsp;μGy/h on a Brazilian black beach (''areia preta'' in Portuguese) composed of [[monazite]].<ref>{{cite book|last=United Nations Scientific Committee on the Effects of Atomic Radiation|author-link=United Nations Scientific Committee on the Effects of Atomic Radiation|title=Sources and Effects of Ionizing Radiation|year=2000|publisher=United Nations|chapter-url=http://www.unscear.org/unscear/publications/2000_1.html|access-date=11 November 2012|page=121|volume=1|chapter=Annex B}}</ref> This rate would convert to 0.8 Gy/a for year-round continuous exposure, but in fact the levels vary seasonally and are much lower in the nearest residences. The record measurement has not been duplicated and is omitted from UNSCEAR's latest reports. Nearby tourist beaches in [[Guarapari]] and [[Cumuruxatiba]] were later evaluated at 14 and 15&nbsp;μGy/h.<ref>{{cite journal|last=Freitas|first=AC|author2=Alencar, AS|title=Gamma dose rates and distribution of natural radionuclides in sand beaches – Ilha Grande, Southeastern Brazil|journal=Journal of Environmental Radioactivity|year=2004|volume=75|issue=2|pages=211–23|doi=10.1016/j.jenvrad.2004.01.002|pmid=15172728|bibcode=2004JEnvR..75..211F |url=http://www.sr2.uerj.br/ceads/artigos_e_livros/Freitas_Antonio-2004-2.pdf|access-date=2 December 2012|issn=0265-931X|url-status=dead|archive-url=https://web.archive.org/web/20140221144543/http://www.sr2.uerj.br/ceads/artigos_e_livros/Freitas_Antonio-2004-2.pdf|archive-date=21 February 2014}}</ref><ref>{{cite conference |url=http://library.sinap.ac.cn/db/hedianwencui201103/%E5%85%A8%E6%96%87/41109077.pdf |title=Natural Radioactivity in Extreme South of Bahia, Brazil Using Gamma-Ray Spectrometry |first=Danilo C. |last=Vasconcelos |date=27 September – 2 October 2009 |conference=International Nuclear Atlantic Conference |conference-url=http://www.inac2011.com.br/ |publisher=Associação Brasileira de Energia Nuclear |location=Rio de Janeiro |isbn=978-85-99141-03-8 |access-date=2 December 2012 |display-authors=etal |archive-date=21 February 2014 |archive-url=https://web.archive.org/web/20140221213504/http://library.sinap.ac.cn/db/hedianwencui201103/%E5%85%A8%E6%96%87/41109077.pdf |url-status=dead }}</ref> Note that the values quoted here are in [[Gray (unit)|Grays]]. To convert to Sieverts (Sv) a radiation weighting factor is required; these weighting factors vary from 1 (beta & gamma) to 20 (alpha particles).

The highest background radiation in an inhabited area is found in [[Ramsar, Mazandaran|Ramsar]], primarily due to the use of local naturally radioactive limestone as a building material. The 1000 most exposed residents receive an average external [[effective radiation dose]] of {{cvt|6|mSv|mrem}} per year, six times the [[ICRP]] recommended limit for exposure to the public from artificial sources.<ref name=HNBR2009 /> They additionally receive a substantial internal dose from radon. Record radiation levels were found in a house where the effective dose due to ambient radiation fields was {{cvt|131|mSv|rem}} per year, and the internal [[committed dose]] from [[radon]] was {{cvt|72|mSv|rem}} per year.<ref name=HNBR2009>{{cite journal|last=Hendry|first=Jolyon H|author2=Simon, Steven L|author3=Wojcik, Andrzej|author4=Sohrabi, Mehdi|author5=Burkart, Werner|author6=Cardis, Elisabeth|author7=Laurier, Dominique|author8=Tirmarche, Margot|author9=Hayata, Isamu|title=Human exposure to high natural background radiation: what can it teach us about radiation risks?|journal=Journal of Radiological Protection|date=1 June 2009|volume=29|issue=2A|pages=A29–A42|doi=10.1088/0952-4746/29/2A/S03|pmid=19454802|pmc=4030667|url=http://cricket.biol.sc.edu/papers/natural/Hendry%20et%20al%202009.pdf|access-date=1 December 2012|bibcode=2009JRP....29...29H|archive-url=https://web.archive.org/web/20131021233519/http://cricket.biol.sc.edu/papers/natural/Hendry%20et%20al%202009.pdf|archive-date=21 October 2013|url-status=dead}}</ref> This unique case is over 80 times higher than the world average natural human exposure to radiation.

Epidemiological studies are underway to identify health effects associated with the high radiation levels in Ramsar. It is much too early to draw unambiguous statistically significant conclusions.<ref name=HNBR2009 /> While so far support for beneficial effects of chronic radiation (like longer lifespan) has been observed in few places only,<ref name=HNBR2009/> a protective and adaptive effect is suggested by at least one study whose authors nonetheless caution that data from Ramsar are not yet sufficiently strong to relax existing regulatory dose limits.<ref>{{cite journal|last=Ghiassi-nejad|first=M|author2=Mortazavi, SM|author3= Cameron, JR|author4= Niroomand-rad, A|author5= Karam, PA|title=Very high background radiation areas of Ramsar, Iran: preliminary biological studies|journal=Health Physics|date=January 2002|volume=82|issue=1|pmid=11769138|url=http://www.probeinternational.org/Ramsar.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.probeinternational.org/Ramsar.pdf |archive-date=2022-10-09 |url-status=live|access-date=11 November 2012|quote=Our preliminary studies seem to indicate the presence of adaptive response in the cells of some Ramsar residents, but we do not claim to have seen hormetic effects in any of those studied. Given the apparent lack of ill effects among observed populations of these high dose rate areas, these data suggest that current dose limits may be overly conservative. However, the available data do not seem sufficient to cause national or international advisory bodies to change their current conservative radiation protection recommendations;|pages=87–93 [92]|doi=10.1097/00004032-200201000-00011|bibcode=2002HeaPh..82...87G|s2cid=26685238}}</ref> However, the recent statistical analyses discussed that there is no correlation between the risk of negative health effects and elevated level of natural background radiation.<ref>{{cite journal |last=Dobrzyński |first=L. |author2=Fornalski, K.W. |author3=Feinendegen, L.E. |pmid=26674931 |title=Cancer Mortality Among People Living in Areas With Various Levels of Natural Background Radiation |year=2015 |journal=Dose-Response |doi=10.1177/1559325815592391 |issue=3 |volume=13 |pages=1–10 |pmc=4674188}}</ref>

===Photoelectric===
Background radiation doses in the immediate vicinity of particles of high atomic number materials, within the human body, have a small enhancement due to the [[photoelectric effect]].<ref>{{cite journal |pages=603–11 |doi=10.1098/rsif.2009.0300 |pmid=19776147 |title=Enhancement of natural background gamma-radiation dose around uranium microparticles in the human body |year=2009 |last1=Pattison |first1=J. E. |last2=Hugtenburg |first2=R. P. |last3=Green |first3=S. |journal=Journal of the Royal Society Interface |volume=7 |issue=45|pmc=2842777 }}</ref>

===Neutron background===
Most of the natural neutron background is a product of cosmic rays interacting with the atmosphere. The neutron energy peaks at around 1&nbsp;MeV and rapidly drops above. At sea level, the production of neutrons is about 20 neutrons per second per kilogram of material interacting with the cosmic rays (or, about 100–300 neutrons per square meter per second). The flux is dependent on geomagnetic latitude, with a maximum near the magnetic poles. At solar minimums, due to lower solar magnetic field shielding, the flux is about twice as high vs the solar maximum. It also dramatically increases during solar flares. In the vicinity of larger heavier objects, e.g. buildings or ships, the neutron flux measures higher; this is known as "cosmic ray induced neutron signature", or "ship effect" as it was first detected with ships at sea.<ref name="DetNuc"/>