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The becquerel is the SI unit of radioactivity, defined as one activity per second, representing the rate of radioactive decay events. It is used to measure the strength of radionuclide emissions, with larger SI multiples commonly applied in health-related contexts due to the unit's small scale. The becquerel honors Henri Becquerel, who, along with Pierre and Marie Curie, received the Nobel Prize in Physics in 1903 for their pioneering research on radioactivity.

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Definition

1 Bq = 1 s−1

A special name was introduced for the reciprocal second (s−1) to represent radioactivity to avoid potentially dangerous mistakes with prefixes. For example, 1 μs−1 would mean 106 disintegrations per second: (10−6 s)−1 = 106 s−1,4 whereas 1 μBq would mean 1 disintegration per 1 million seconds: 10–6 s–1. 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).5 The hertz is now only used for periodic phenomena.6 While 1 Hz replaces the deprecated term cycle per second, 1 Bq refers to one event per second on average for aperiodic radioactive decays.

The gray (Gy) and the becquerel (Bq) were introduced in 1975.7 Between 1953 and 1975, absorbed dose was often measured with the rad. Decay activity was given with the curie before 1946 and often with the rutherford between 19468 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.9

Like any SI unit, Bq can be prefixed; commonly used multiples are kBq (kilobecquerel, 103 Bq), MBq (megabecquerel, 106 Bq, equivalent to 1 rutherford), GBq (gigabecquerel, 109 Bq), TBq (terabecquerel, 1012 Bq), and PBq (petabecquerel, 1015 Bq). Large prefixes are common for practical uses of the unit.

Examples

For practical applications, 1 Bq is a small unit. For example, there is roughly 0.017 g of potassium-40 in a typical human body, producing about 4,400 decays per second (Bq).10

The activity of radioactive americium in a home smoke detector is about 37 kBq (1 μCi).11

The global inventory of carbon-14 is estimated to be 8.5×1018 Bq (8.5 EBq, 8.5 exabecquerel).12

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

The becquerel succeeded the curie (Ci),13 an older, non-SI unit of radioactivity based on the activity of 1 gram of radium-226. The curie is defined as 3.7×1010 s−1, or 37 GBq.1415

Conversion factors:

  • 1 Ci = 3.7×1010 Bq = 37 GBq
  • 1 μCi = 37000 Bq = 37 kBq
  • 1 Bq = 2.7×10−11 Ci = 2.7×10−5 μCi
  • 1 MBq = 0.027 mCi

The following table shows radiation quantities in SI and non-SI units. WR (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.16[not specific enough to verify]

Ionizing radiation related quantities
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QuantityUnitSymbolDerivationYearSI equivalent
Activity (A)becquerelBqs−11974SI unit
curieCi3.7×1010 s−119533.7×1010 Bq
rutherfordRd106 s−119461000000 Bq
Exposure (X)coulomb per kilogramC/kgC⋅kg−1 of air1974SI unit
röntgenResu / 0.001293 g of air19282.58×10−4 C/kg
Absorbed dose (D)grayGyJ⋅kg−11974SI unit
erg per gramerg/gerg⋅g−119501.0×10−4 Gy
radrad100 erg⋅g−119530.010 Gy
Equivalent dose (H)sievertSvJ⋅kg−1 × WR1977SI unit
röntgen equivalent manrem100 erg⋅g−1 × WR19710.010 Sv
Effective dose (E)sievertSvJ⋅kg−1 × WR × WT1977SI unit
röntgen equivalent manrem100 erg⋅g−1 × WR × WT19710.010 Sv

See also

Look up becquerel in Wiktionary, the free dictionary.

References

  1. "Radioactivity: Radioactive Activity Doses". radioactivity.eu.com. Archived from the original on 2020-02-20. Retrieved 2020-02-20. https://web.archive.org/web/20200220103556/https://radioactivity.eu.com/site/pages/Activity_Doses.htm ↩

  2. "What are the Units of Radiation Activity?". ehs.stanford.edu. https://ehs.stanford.edu/manual/radiation-protection-guidance-hospital-staff/what-are-units-radiation-activity ↩

  3. "BIPM - Becquerel". BIPM. Retrieved 2012-10-24. http://www.bipm.org/en/si/history-si/radioactivity/becquerel.html ↩

  4. Allisy, A. (1995), "From the curie to the becquerel", Metrologia, 32 (6): 467–479, Bibcode:1995Metro..31..467A, doi:10.1088/0026-1394/31/6/006, S2CID 250749337 /wiki/Bibcode_(identifier) ↩

  5. Allisy, A. (1995), "From the curie to the becquerel", Metrologia, 32 (6): 467–479, Bibcode:1995Metro..31..467A, doi:10.1088/0026-1394/31/6/006, S2CID 250749337 /wiki/Bibcode_(identifier) ↩

  6. "BIPM - Table 3". BIPM. Retrieved 2015-07-19. (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. http://www.bipm.org/en/publications/si-brochure/section2-2.html#section2-2-2 ↩

  7. Harder, D (1976), "[The new radiologic units of measurement gray and becquerel (author's translation from the German original)]", Röntgen-Blätter, 29 (1): 49–52, PMID 1251122. /wiki/PMID_(identifier) ↩

  8. Lind, SC (1946), "New units for the measurement of radioactivity", Science, 103 (2687): 761–762, Bibcode:1946Sci...103..761L, doi:10.1126/science.103.2687.761-a, PMID 17836457, S2CID 5343688. /wiki/Bibcode_(identifier) ↩

  9. "SI Brochure: The International System of Units (SI)". SI Brochure (8 ed.). BIPM. 2014. http://www.bipm.org/en/publications/si-brochure/section5-2.html ↩

  10. "Radioactive Human Body". Harvard Natural Sciences Lecture Demonstrations. https://sciencedemonstrations.fas.harvard.edu/presentations/radioactive-human-body ↩

  11. "Smoke Detector (1970s)". Museum of Radiation and Radioactivity. Retrieved 25 September 2023. https://orau.org/health-physics-museum/collection/consumer/miscellaneous/smoke-detector.html ↩

  12. G.R. Choppin, J.O.Liljenzin, J. Rydberg, "Radiochemistry and Nuclear Chemistry", 3rd edition, Butterworth-Heinemann, 2002. ISBN 978-0-7506-7463-8. /wiki/Jan-Olov_Liljenzin ↩

  13. It was adopted by the BIPM in 1975, see resolution 8 of the 15th CGPM meeting http://www.bipm.org/en/CGPM/db/15/8/ ↩

  14. Allisy, A. (1995), "From the curie to the becquerel", Metrologia, 32 (6): 467–479, Bibcode:1995Metro..31..467A, doi:10.1088/0026-1394/31/6/006, S2CID 250749337 /wiki/Bibcode_(identifier) ↩

  15. Resolution 7 of the 12th CGPM Archived 2021-02-19 at the Wayback Machine (1964) https://www.bipm.org/en/CGPM/db/12/7/ ↩

  16. Baes, Fred. "hps.org". Health Physics Society. Retrieved 2022-10-03. http://hps.org/ ↩