View source for Becquerel

{{Short description|SI derived unit of radioactivity}}
{{Redirect-multi|2|Bq|MBq|other uses|BQ (disambiguation){{!}}BQ|and|MBQ (disambiguation){{!}}MBQ|and|Becquerel (disambiguation)}}
{{Infobox Unit
| name         = becquerel
| image        = Radium 226 radiation source 1.jpg
| caption      = [[Radium-226]] radiation source. Activity 3300&nbsp;Bq (3.3&nbsp;kBq)
| standard     = [[SI]]
| quantity     = [[Specific activity|activity]]
| symbol       = Bq 
| namedafter   = [[Henri Becquerel]]
| units1       = [[Rutherford (unit)|rutherford]]
| inunits1     = {{val|e=-6|u=Rd}}
| units2       = [[Curie (unit)|curie]]
| inunits2     = {{val|2.703|e=-11|u=Ci}} ≅ {{val|27|u=pCi}}
| units3       = [[SI base unit]]
| inunits3     = [[second|s]]<sup>−1</sup>
}}

The '''becquerel''' ({{IPAc-en|ˌ|b|ɛ|k|ə|ˈ|r|ɛ|l|audio=LL-Q1860 (eng)-NaomiAmethyst-becquerel.wav}}; symbol: '''Bq''') is the unit of [[radioactive decay|radioactivity]] in the [[International System of Units]] (SI). One becquerel is defined as an [[activity (radioactivity)|activity]] of one per [[second]], on average, for aperiodic activity events referred to a [[radionuclide]]. For applications relating to human health this is a small quantity,<ref>{{cite web |title=Radioactivity: Radioactive Activity Doses |url=https://radioactivity.eu.com/site/pages/Activity_Doses.htm |url-status=dead |archive-url=https://web.archive.org/web/20200220103556/https://radioactivity.eu.com/site/pages/Activity_Doses.htm |archive-date=2020-02-20 |access-date=2020-02-20 |website=radioactivity.eu.com}}</ref> and [[SI multiple]]s of the unit are commonly used.<ref>{{cite web |title=What are the Units of Radiation Activity? |url=https://ehs.stanford.edu/manual/radiation-protection-guidance-hospital-staff/what-are-units-radiation-activity |website=ehs.stanford.edu |access-date=}}</ref>

The becquerel is named after [[Henri Becquerel]], who shared a [[Nobel Prize in Physics]] with [[Pierre Curie|Pierre]] and [[Marie  Curie]] in 1903 for their work in discovering radioactivity.<ref name="BIPMBecquerel">{{cite web|url=http://www.bipm.org/en/si/history-si/radioactivity/becquerel.html|title=BIPM - Becquerel|publisher=[[BIPM]]|access-date=2012-10-24}}</ref>

==Definition==
1&nbsp;Bq = 1&nbsp;s<sup>−1</sup>

A special name was introduced for the [[Inverse second|reciprocal second]] (s{{sup|−1}}) to represent radioactivity to avoid potentially dangerous mistakes with prefixes. For example, 1&nbsp;μs{{sup|−1}} would mean 10{{sup|6}} disintegrations per second: {{nowrap|1=({{val|e=−6|u=s}}){{sup|−1}} = {{val|e=6|u=s-1}}}},<ref name="Allisy">{{Citation|last=Allisy|first= A.|title=From the curie to the becquerel|journal=Metrologia|volume=32|issue=6|year=1995|pages=467–479|doi=10.1088/0026-1394/31/6/006|bibcode = 1995Metro..31..467A|s2cid= 250749337}}</ref> whereas 1&nbsp;μBq would mean 1 disintegration per 1 million seconds: {{nowrap|1=10<sup>–6</sup> s<sup>–1</sup>}}. Other names considered were [[hertz]] (Hz), a special name already in use for the reciprocal second (for ''periodic'' events of any kind), and fourier (Fr; after [[Joseph Fourier]]).<ref name="Allisy" /> The hertz is now only used for periodic phenomena.<ref name="BIPMtable3">{{cite web|url=http://www.bipm.org/en/publications/si-brochure/section2-2.html#section2-2-2|title=BIPM - Table 3|publisher=[[BIPM]]|quote=(d) The hertz (one per second) is used ''only'' for periodic phenomena, and the becquerel (also one per second) is used ''only'' for stochastic processes in activity referred to a radionuclide.|access-date=2015-07-19}}</ref> While 1&nbsp;Hz replaces the deprecated term [[cycle per second]], 1 Bq refers to one event per second on average for [[aperiodic frequency|aperiodic]] radioactive decays.

The [[gray (unit)|gray]] (Gy) and the becquerel (Bq) were introduced in 1975.<ref name="pmid_1251122">{{Citation|last=Harder|first=D|year=1976|title=[The new radiologic units of measurement gray and becquerel (author's translation from the German original)]|journal=Röntgen-Blätter|volume=29|issue=1 |pages=49–52 |pmid=1251122 |postscript=.}}</ref> Between 1953 and 1975, absorbed dose was often measured with the [[rad (unit)|rad]]. Decay activity was given with the [[Curie (unit)|curie]] before 1946 and often with the [[rutherford (unit)|rutherford]] between 1946<ref name="pmid_17836457">{{Citation|last=Lind|first=SC|year=1946|title=New units for the measurement of radioactivity|journal=Science|volume=103|issue=2687|pages=761–762|pmid=17836457|doi=10.1126/science.103.2687.761-a|postscript=.|bibcode=1946Sci...103..761L |s2cid=5343688 }}</ref> and 1975.

== Unit capitalization and prefixes ==
As with every International System of Units (SI) unit named after a person, the first letter of its symbol is uppercase (Bq). However, when an SI unit is spelled out in English, it should always begin with a lowercase letter (becquerel)—except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in material using [[title case]].<ref>
{{cite web|title=SI Brochure: The International System of Units (SI)|url=http://www.bipm.org/en/publications/si-brochure/section5-2.html|edition=8|date=2014|work=SI Brochure|publisher=[[BIPM]]}}</ref>

Like any SI unit, Bq can be [[SI prefix|prefixed]]; commonly used multiples are kBq (kilobecquerel, {{val|e=3|u=Bq}}), MBq (megabecquerel, {{val|e=6|u=Bq}}, equivalent to 1 [[rutherford (unit)|rutherford]]), GBq (gigabecquerel, {{val|e=9|u=Bq}}), TBq (terabecquerel, {{val|e=12|u=Bq}}), and PBq (petabecquerel, {{val|e=15|u=Bq}}). Large prefixes are common for practical uses of the unit.

== Examples ==
For practical applications, 1&nbsp;Bq is a small unit. For example, there is roughly 0.017&nbsp;g of [[potassium-40]] in a typical human body, producing about 4,400 decays per second (Bq).<ref>{{Cite web |title=Radioactive Human Body |url=https://sciencedemonstrations.fas.harvard.edu/presentations/radioactive-human-body |website=Harvard Natural Sciences Lecture Demonstrations}}</ref>

The activity of radioactive [[americium]] in a home [[smoke detector]] is about 37&nbsp;kBq (1&nbsp;μCi).<ref>{{cite web |title=Smoke Detector (1970s) |url=https://orau.org/health-physics-museum/collection/consumer/miscellaneous/smoke-detector.html |website=Museum of Radiation and Radioactivity |access-date=25 September 2023 |language=en}}</ref>

The global inventory of [[carbon-14]] is estimated to be {{val|8.5|e=18|u=Bq}} (8.5&nbsp;EBq, 8.5 [[exa]]becquerel).<ref>G.R. Choppin, [[Jan-Olov Liljenzin|J.O.Liljenzin]], J. Rydberg, "Radiochemistry and Nuclear Chemistry", 3rd edition, Butterworth-Heinemann, 2002. {{ISBN|978-0-7506-7463-8}}.</ref>

These examples are useful for comparing the amount of activity of these radioactive materials, but should not be confused with the amount of exposure to [[ionizing radiation]] that these materials represent. The level of exposure and thus the [[absorbed dose]] received are what should be considered when assessing the effects of ionizing radiation on humans.

== Relation to the curie ==
{{radiation_units.svg}}
The becquerel succeeded the [[Curie (unit)|curie]] (Ci),<ref>It was adopted by the BIPM in 1975, see [http://www.bipm.org/en/CGPM/db/15/8/ resolution 8 of the 15th CGPM meeting]</ref> an older, non-SI unit of radioactivity based on the activity of 1&nbsp;gram of [[radium-226]]. The curie is defined as {{val|3.7|e=10|u=s-1}}, or 37&nbsp;GBq.<ref name="Allisy" /><ref>[https://www.bipm.org/en/CGPM/db/12/7/ Resolution 7 of the 12th CGPM] {{Webarchive|url=https://web.archive.org/web/20210219084448/https://www.bipm.org/en/CGPM/db/12/7 |date=2021-02-19 }} (1964)</ref>

Conversion factors:
* 1&nbsp;Ci = {{val|3.7|e=10|u=Bq}} = 37&nbsp;GBq
* 1&nbsp;μCi = {{val|37,000|u=Bq}} = 37&nbsp;kBq
* 1&nbsp;Bq = {{val|2.7|e=-11|u=Ci}} = {{val|2.7|e=-5|u=μCi}}
* 1&nbsp;MBq = 0.027&nbsp;mCi

== Relation to other radiation-related quantities ==
[[File:Radioactivity and radiation.png|thumb|upright=2|Graphic showing relationships between radioactivity and detected ionizing radiation]]
The following table shows radiation quantities in SI and non-SI units. [[Sievert#Calculating protection dose quantities|''W''{{sub|''R''}}]] (formerly 'Q' factor) is a factor that scales the biological effect for different types of radiation, relative to x-rays (e.g. 1 for beta radiation, 20 for alpha radiation, and a complicated function of energy for neutrons). In general, conversion between rates of emission, the density of radiation, the fraction absorbed, and the biological effects, requires knowledge of the geometry between source and target, the energy and the type of the radiation emitted, among other factors.<ref>{{Cite web |last=Baes |first=Fred |title=hps.org |url=http://hps.org/ |access-date=2022-10-03 |website=Health Physics Society}}</ref>{{nonspecific|date=January 2024}}

{{Radiation related quantities}}

== See also ==
* [[Background radiation]]
* [[Banana equivalent dose]]
* [[Counts per minute]]
* [[Orders of magnitude (radiation)]]
* [[Radiation poisoning]]
* [[Relative biological effectiveness]]

== References ==
{{reflist|2}}

== External links ==
{{wiktionary}}
* [https://web.archive.org/web/20050316054529/http://www1.bipm.org/en/si/derived_units/2-2-2.html Derived units] on the [[International Bureau of Weights and Measures]] (BIPM) web site
{{Radiation protection}}
{{SI units}}
{{Ionising radiation related quantities}}
[[Category:SI derived units]]
[[Category:Units of radioactivity]]
[[Category:Units of frequency]]