Becquerel

The becquerel (English: /bɛkəˈrɛl/; symbol: Bq) is the SI derived unit of radioactivity. One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays 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 Skłodowska 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: 1·(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).^[4] The hertz is now only used for periodic phenomena.^[5] Whereas 1 Hz is 1 cycle per second, 1 Bq is 1 aperiodic radioactivity event per second.

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 for 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.

Calculation of radioactivity

For a given mass m (in grams) of an isotope with atomic mass \( {\displaystyle m_{\text{a}}} \) (in g/mol) and a half-life of \( t_{1/2} \) (in s), the radioactivity can be calculated using:

\( {\displaystyle A_{\text{Bq}}={\frac {m}{m_{\text{a}}}}N_{\text{A}}{\frac {\ln 2}{t_{1/2}}}} \)

With \(} N_{{\text{A}}} \) = 6.02214076×1023 mol−1, the Avogadro constant.

Since \( {\displaystyle m/m_{\text{a}}} \)is the number of moles ( n), the amount of radioactivity A can be calculated by:

\( {\displaystyle A_{\text{Bq}}=nN_{\text{A}}{\frac {\ln 2}{t_{1/2}}}} \)

For instance, on average each gram of potassium contains 0.000117 gram of 40K (all other naturally occurring isotopes are stable) that has a \( t_{1/2} \) of 1.277×10⁹ years = 4.030×10¹⁶ s,[9] and has an atomic mass of 39.964 g/mol,[10] so the amount of radioactivity associated with a gram of potassium is 30 Bq.
Examples

For practical applications, 1 Bq is a small unit. For example, the roughly 0.0169 g of potassium-40 present in a typical human body produces approximately 4,400 disintegrations per second or 4.4 kBq of activity.^[11]

The global inventory of carbon-14 is estimated to be 8.5×10¹⁸ Bq (8.5 EBq, 8.5 exabecquerel).^[12] The nuclear explosion in Hiroshima (an explosion of 16 kt or 67 TJ) is estimated to have produced 8×10²⁴ Bq (8 YBq, 8 yottabecquerel).^[13]

These examples are useful for comparing the amount 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),^[14] 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]

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. 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. [15]

Ionizing radiation related quantities
Quantity	Unit	Symbol	Derivation	Year	SI equivalence
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 x W_R	1971	0.010 Sv
Effective dose (E)	sievert	Sv	J⋅kg⁻¹ × W_R x W_T	1977	SI unit
Effective dose (E)	röntgen equivalent man	rem	100 erg⋅g⁻¹ x W_R x W_T	1971	0.010 Sv

See also

Background radiation
Banana equivalent dose
Counts per minute
Ionizing radiation
Orders of magnitude (radiation)
Radiation poisoning
Relative biological effectiveness
Rem (unit)
Rutherford (unit)
Sievert (biological dose equivalent of radiation)

References

"Radioactivity : Radioactive Activity Doses". www.radioactivity.eu.com. Retrieved 20 February 2020.
"Radiation Protection Guidance For Hospital Staff – Stanford Environmental Health & Safety". ehs.stanford.edu. Retrieved 20 February 2020.
"BIPM - Becquerel". BIPM. Retrieved 2012-10-24.
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
"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.
"SI Brochure: The International System of Units (SI)". SI Brochure (8 ed.). BIPM. 2014.
"Table of Isotopes decay data". Lund University. 1990-06-01. Retrieved 2014-01-12.
"Atomic Weights and Isotopic Compositions for All Elements". NIST. Retrieved 2014-01-12.
Radioactive human body — Harvard University Natural Science Lecture Demonstrations - Accessed October 2013
G.R. Choppin, J.O.Liljenzin, J. Rydberg, "Radiochemistry and Nuclear Chemistry", 3rd edition, Butterworth-Heinemann, 2002. ISBN 978-0-7506-7463-8.
Michael J. Kennish, Pollution Impacts on Marine Biotic Communities , CRC Press, 1998, p. 74. ISBN 978-0-8493-8428-8.
It was adopted by the BIPM in 1975, see resolution 8 of the 15th CGPM meeting

http://hps.org/publicinformation/ate/faqs/gammaandexposure.html

External links
Look up becquerel in Wiktionary, the free dictionary.

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

vte

Radiation protection
Main articles

Background radiation Dosimetry Health physics Ionizing radiation Internal dosimetry Radioactive contamination Radioactive sources Radiobiology

Measurement
quantities and units

Absorbed dose Becquerel Committed dose Computed tomography dose index Counts per minute Effective dose Equivalent dose Gray Mean glandular dose Monitor unit Rad Roentgen Rem Sievert

Instruments and
measurement techniques

Airborne radioactive particulate monitoring Dosimeter Geiger counter Ion chamber Scintillation counter Proportional counter

Radiation monitoring Semiconductor detector Survey meter Whole-body counting

Protection techniques

Lead shielding Glovebox Potassium iodide Radon mitigation Respirators

Organisations

Euratom HPS (USA) IAEA ICRU ICRP IRPA SRP (UK) UNSCEAR

Regulation

IRR (UK) NRC (USA) ONR (UK) Radiation Protection Convention, 1960

Radiation effects

Acute radiation syndrome Radiation-induced cancer

See also: the categories Medical physics, Radiation effects, Radioactivity, Radiobiology, and Radiation protection.

vte

SI units
Base units

ampere candela kelvin kilogram metre mole second

The SI logo
Derived units
with special names

becquerel coulomb degree Celsius farad gray henry hertz joule katal lumen lux newton ohm pascal radian siemens sievert steradian tesla volt watt weber

Other accepted units

astronomical unit dalton day decibel degree of arc electronvolt hectare hour litre minute minute and second of arc neper tonne