Editing Carbon-14 (section)

===In the human body===
Since many sources of human food are ultimately derived from terrestrial plants, the relative concentration of {{sup|14}}C in human bodies is nearly identical to the relative concentration in the atmosphere. The rates of disintegration of [[potassium-40]] ({{sup|40}}K) and {{sup|14}}C in the normal adult body are comparable (a few thousand decays per second).<ref>{{cite web | vauthors = Rowland RE | url = http://www.rerowland.com/BodyActivity.htm | title = The Radioactivity of the Normal Adult Body | archive-url = https://web.archive.org/web/20110205025628/http://www.rerowland.com/BodyActivity.htm | archive-date=2011-02-05 | work = rerowland.com }}</ref> The beta decays from external (environmental) radiocarbon contribute about 0.01&nbsp;[[mSv]]/year (1&nbsp;mrem/year) to each person's [[Equivalent dose|dose]] of [[ionizing radiation]].<ref>{{cite book| title=Ionizing Radiation Exposure of the Population of the United States {{!}} NCRP Report No. 93 | publisher=National Council on Radiation Protection and Measurements | year=1987 | url = http://lbl.gov/abc/wallchart/chapters/15/3.html | archive-url = https://web.archive.org/web/20070711052408/http://www.lbl.gov/abc/wallchart/chapters/15/3.html | archive-date=2007-07-11 }})</ref> This is small compared to the doses from potassium-40, {{sup|40}}K (0.39&nbsp;mSv/year) and [[radon]] (variable depending on where you live).

{{sup|14}}C can be used as a [[radioactive tracer]] in medicine. In the initial variant of the [[urea breath test]], a diagnostic test for ''[[Helicobacter pylori]]'', urea labeled with about {{convert|37|kBq|uCi|abbr=on|lk=on}} {{sup|14}}C is fed to a patient (i.e. 37,000 decays per second). In the event of a ''H. pylori'' infection, the bacterial [[urease]] enzyme breaks down the [[urea]] into [[ammonia]] and radioactively-labeled [[carbon dioxide]], which can be detected by low-level counting of the patient's breath.<ref>{{cite web|title=Society of Nuclear Medicine Procedure Guideline for C-14 Urea Breath Test |date=2001-06-23 |url=http://interactive.snm.org/docs/pg_ch07_0403.pdf |access-date=2007-07-04 |work=snm.org |url-status=dead |archive-url=https://web.archive.org/web/20070926152956/http://interactive.snm.org/docs/pg_ch07_0403.pdf |archive-date=2007-09-26 }}</ref>