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becquerel
Radium-226 radiation source. Activity 3300 Bq (3.3 kBq)
General information
Unit system	SI
Unit of	activity
Symbol	Bq
Named after	Henri Becquerel
Conversions
1 Bq in ...	... is equal to ...
rutherford	10 Rd
curie	2.703×10 Ci ≅ 27 pCi
SI base unit	s

The becquerel (/ˌbɛkəˈrɛl/; symbol: Bq) is the unit of radioactivity in the International System of Units (SI). One becquerel is defined as an 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, and SI multiples of the unit are commonly used.

The becquerel is named after Henri Becquerel, who shared a Nobel Prize in Physics with Pierre and Marie Curie in 1903 for their work in discovering radioactivity.

Definition

1 Bq = 1 s

A special name was introduced for the reciprocal second (s) to represent radioactivity to avoid potentially dangerous mistakes with prefixes. For example, 1 μs would mean 10 disintegrations per second: (10 s) = 10 s, whereas 1 μBq would mean 1 disintegration per 1 million seconds. 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). The hertz is now only used for periodic phenomena. 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. 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 1946 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.

Like any SI unit, Bq can be prefixed; commonly used multiples are kBq (kilobecquerel, 10 Bq), MBq (megabecquerel, 10 Bq, equivalent to 1 rutherford), GBq (gigabecquerel, 10 Bq), TBq (terabecquerel, 10 Bq), and PBq (petabecquerel, 10 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).

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

The global inventory of carbon-14 is estimated to be 8.5×10 Bq (8.5 EBq, 8.5 exabecquerel).

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), an older, non-SI unit of radioactivity based on the activity of 1 gram of radium-226. The curie is defined as 3.7×10 s, or 37 GBq.

Conversion factors:

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

Relation to other radiation-related quantities

The following table shows radiation quantities in SI and non-SI units. W_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.

See also

• Background radiation
• Banana equivalent dose
• Counts per minute
• Ionizing radiation
• Orders of magnitude (radiation)
• Radiation poisoning
• Relative biological effectiveness

References

1. "Radioactivity: Radioactive Activity Doses". radioactivity.eu.com. Archived from the original on 2020-02-20. Retrieved 2020-02-20.
2. "What are the Units of Radiation Activity?". ehs.stanford.edu.
3. "BIPM - Becquerel". BIPM. Retrieved 2012-10-24.
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
5. "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.
6. Harder, D (1976), "", Röntgen-Blätter, 29 (1): 49–52, PMID 1251122.
7. 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.
8. "SI Brochure: The International System of Units (SI)". SI Brochure (8 ed.). BIPM. 2014.
9. "Radioactive Human Body". Harvard Natural Sciences Lecture Demonstrations.
10. "Smoke Detector (1970s)". Museum of Radiation and Radioactivity. Retrieved 25 September 2023.
11. G.R. Choppin, J.O.Liljenzin, J. Rydberg, "Radiochemistry and Nuclear Chemistry", 3rd edition, Butterworth-Heinemann, 2002. ISBN 978-0-7506-7463-8.
12. It was adopted by the BIPM in 1975, see resolution 8 of the 15th CGPM meeting
13. Resolution 7 of the 12th CGPM Archived 2021-02-19 at the Wayback Machine (1964)
14. Baes, Fred. "hps.org". Health Physics Society. Retrieved 2022-10-03.

External links

• Derived units on the International Bureau of Weights and Measures (BIPM) web site

• SI derived units
• Units of radioactivity
• Units of frequency