Becquerel

becquerel
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	10−6 Rd
curie	2.703×10−11 Ci ≅ 27 pCi
SI base unit	s−1

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 decay per second. For applications relating to human health this is a small quantity,^[1] and SI multiples of the unit are commonly used.^[2]

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.^[3]

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. Other names considered were hertz (Hz), a special name already in use for the reciprocal second, and fourier (Fr; after Joseph Fourier).^[4] The hertz is now only used for periodic phenomena.^[5] While 1 Hz is one cycle per second, 1 Bq is one event per second on average for aperiodic radioactive decays.

The gray (Gy) and the becquerel (Bq) were introduced in 1975.^[6] Between 1953 and 1975, absorbed dose was often measured in rads. Decay activity was measured in curies before 1946 and often in rutherfords between 1946^[7] 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.^[8]

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).^[9]

The activity of radioactive americium in a home smoke detector is about 37 kBq (1 μCi).^[10]

The global inventory of carbon-14 is estimated to be 8.5×10¹⁸ Bq (8.5 EBq, 8.5 exabecquerel).^[11]

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),^[12] 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.^[4]^[13]

Conversion factors:

1 Ci = 3.7×10¹⁰ Bq = 37 GBq
1 μCi = 37,000 Bq = 37 kBq
1 Bq = 2.7×10⁻¹¹ Ci = 2.7×10⁻⁵ μCi
1 MBq = 0.027 mCi

Relation to other radiation-related quantities

Graphic showing relationships between radioactivity and detected ionizing radiation

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.^[14]^{[not specific enough to verify]}

Ionizing radiation related quantities
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Quantity	Unit	Symbol	Derivation	Year	SI equivalent
Activity (A)	becquerel	Bq	s⁻¹	1974	SI unit
	curie	Ci	3.7 × 10¹⁰ s⁻¹	1953	3.7×10¹⁰ Bq
	rutherford	Rd	10⁶ s⁻¹	1946	1,000,000 Bq
Exposure (X)	coulomb per kilogram	C/kg	C⋅kg⁻¹ of air	1974	SI unit
Exposure (X)	röntgen	R	esu / 0.001293 g of air	1928	2.58 × 10⁻⁴ C/kg
Absorbed dose (D)	gray	Gy	J⋅kg⁻¹	1974	SI unit
	erg per gram	erg/g	erg⋅g⁻¹	1950	1.0 × 10⁻⁴ Gy
	rad	rad	100 erg⋅g⁻¹	1953	0.010 Gy
Equivalent dose (H)	sievert	Sv	J⋅kg⁻¹ × W_R	1977	SI unit
Equivalent dose (H)	röntgen equivalent man	rem	100 erg⋅g⁻¹ × W_R	1971	0.010 Sv
Effective dose (E)	sievert	Sv	J⋅kg⁻¹ × W_R × W_T	1977	SI unit
Effective dose (E)	röntgen equivalent man	rem	100 erg⋅g⁻¹ × W_R × W_T	1971	0.010 Sv

References

^ "Radioactivity: Radioactive Activity Doses". radioactivity.eu.com. Archived from the original on 2020-02-20. Retrieved 2020-02-20.
^ "Radiation Protection Guidance For Hospital Staff – Stanford Environmental Health & Safety". ehs.stanford.edu. Retrieved 2020-02-20.
^ "BIPM - Becquerel". BIPM. Retrieved 2012-10-24.
^ ^a ^b ^c 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
^ "BIPM - Table 3". BIPM. Retrieved 2015-07-19. (d) The hertz is used only for periodic phenomena, and the becquerel is used only for stochastic processes in activity referred to a radionuclide.
^ 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.
^ 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.
^ "SI Brochure: The International System of Units (SI)". SI Brochure (8 ed.). BIPM. 2014.
^ "Radioactive Human Body". Harvard Natural Sciences Lecture Demonstrations.
^ "Smoke Detector (1970s)". Museum of Radiation and Radioactivity. Retrieved 25 September 2023.
^ G.R. Choppin, J.O.Liljenzin, J. Rydberg, "Radiochemistry and Nuclear Chemistry", 3rd edition, Butterworth-Heinemann, 2002. ISBN 978-0-7506-7463-8.
^ It was adopted by the BIPM in 1975, see resolution 8 of the 15th CGPM meeting
^ Resolution 7 of the 12th CGPM Archived 2021-02-19 at the Wayback Machine (1964)
^ Baes, Fred. "hps.org". Health Physics Society. Retrieved 2022-10-03.