Editing Americium (section)

===Ionization-type smoke detector===
{{Main|Smoke detector#Ionization}}

Americium is used in the most common type of household [[smoke detector]], which uses <sup>241</sup>Am in the form of americium dioxide as its source of [[ionizing radiation]].<ref>{{citation |url=http://www.uic.com.au/nip35.htm |archive-url=http://webarchive.loc.gov/all/20020911070229/http%3A//www%2Euic%2Ecom%2Eau/nip35%2Ehtm |archive-date= 11 September 2002 |title=Smoke Detectors and Americium |work=Nuclear Issues Briefing Paper |volume=35 |date=May 2002 |access-date=2015-08-26}}</ref> This isotope is preferred over <sup>226</sup>[[radium|Ra]] because it emits 5 times more alpha particles and relatively little harmful gamma radiation.

The amount of americium in a typical new smoke detector is 1&nbsp;[[microcurie]] (37&nbsp;[[kBq]]) or 0.29 [[microgram]]. This amount declines slowly as the americium decays into [[neptunium]]-237, a different transuranic element with a much longer half-life (about 2.14 million years). With its half-life of 432.2 years, the americium in a smoke detector includes about 3% [[neptunium]] after 19 years, and about 5% after 32 years. The radiation passes through an [[ionization chamber]], an air-filled space between two [[electrode]]s, and permits a small, constant [[Electric current|current]] between the electrodes. Any smoke that enters the chamber absorbs the alpha particles, which reduces the ionization and affects this current, triggering the alarm. Compared to the alternative optical smoke detector, the ionization smoke detector is cheaper and can detect particles which are too small to produce significant light scattering; however, it is more prone to [[Type I and type II errors|false alarms]].<ref>Residential Smoke Alarm Performance, Thomas Cleary. Building and Fire Research Laboratory, National Institute of Standards and Technology; UL Smoke and Fire Dynamics Seminar. November 2007</ref><ref name="NIST">Bukowski, R. W. ''et al''. (2007) [http://www.fire.nist.gov/bfrlpubs/fire07/art063.html Performance of Home Smoke Alarms Analysis of the Response of Several Available Technologies in Residential Fire Settings] {{Webarchive|url=https://web.archive.org/web/20100822192559/http://www.fire.nist.gov/bfrlpubs/fire07/art063.html |date=22 August 2010 }}, NIST Technical Note 1455-1</ref><ref>{{cite web |url=http://media.cns-snc.ca/pdf_doc/ecc/smoke_am241.pdf |archive-url=
https://web.archive.org/web/20160325003327/https://cns-snc.ca/media/uploads/teachers/smoke_am241.pdf|archive-date=2016-03-25|title = Smoke detectors and americium-241 fact sheet|publisher = Canadian Nuclear Society|access-date =31 August 2009}}</ref><ref>{{cite web|url=http://www.atsdr.cdc.gov/toxprofiles/tp156.pdf|title=Toxicological Profile For Americium|author=Gerberding, Julie Louise |publisher=[[United States Department of Health and Human Services]]/[[Agency for Toxic Substances and Disease Registry]]|access-date=29 August 2009|date=2004| archive-url= https://web.archive.org/web/20090906112953/http://www.atsdr.cdc.gov/toxprofiles/tp156.pdf| archive-date= 6 September 2009 | url-status= live}}</ref>