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Radium 226 radiation source 1.jpg
Radium-226 radiation source. Activity 3300 Bq (3.3 kBq)
General information
Unit system SI
Unit of activity
Named after Henri Becquerel
1 Bq in ...... is equal to ...
    rutherford    10−6 Rd
    curie    2.703×10−11 Ci27 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]


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.


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:

Graphic showing relationships between radioactivity and detected ionizing radiation Radioactivity and radiation.png
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. [14] [ not specific enough to verify ]

Ionizing radiation related quantities
QuantityUnitSymbolDerivationYear SI equivalent
Activity (A) becquerel Bqs−11974SI unit
curie Ci3.7 × 1010 s−119533.7×1010 Bq
rutherford Rd106 s−119461,000,000 Bq
Exposure (X) coulomb per kilogram C/kgC⋅kg−1 of air1974SI unit
röntgen R esu / 0.001293 g of air19282.58 × 10−4 C/kg
Absorbed dose (D) gray Gy J⋅kg−11974SI unit
erg per gramerg/gerg⋅g−119501.0 × 10−4 Gy
rad rad100 erg⋅g−119530.010 Gy
Equivalent dose (H) sievert SvJ⋅kg−1 × WR 1977SI unit
röntgen equivalent man rem100 erg⋅g−1 × WR 19710.010 Sv
Effective dose (E) sievert SvJ⋅kg−1 × WR × WT 1977SI unit
röntgen equivalent man rem100 erg⋅g−1 × WR × WT 19710.010 Sv

See also

Related Research Articles

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<span class="mw-page-title-main">Hertz</span> SI unit for frequency

The hertz is the unit of frequency in the International System of Units (SI), equivalent to one event per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one hertz is the reciprocal of one second. It is named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves. Hertz are commonly expressed in multiples: kilohertz (kHz), megahertz (MHz), gigahertz (GHz), terahertz (THz).

<span class="mw-page-title-main">Polonium</span> Chemical element, symbol Po and atomic number 84

Polonium is a chemical element; it has symbol Po and atomic number 84. A rare and highly radioactive metal with no stable isotopes, polonium is a chalcogen and chemically similar to selenium and tellurium, though its metallic character resembles that of its horizontal neighbors in the periodic table: thallium, lead, and bismuth. Due to the short half-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleeting polonium-210 in uranium ores, as it is the penultimate daughter of natural uranium-238. Though longer-lived isotopes exist, such as the 124 years half-life of polonium-209, they are much more difficult to produce. Today, polonium is usually produced in milligram quantities by the neutron irradiation of bismuth. Due to its intense radioactivity, which results in the radiolysis of chemical bonds and radioactive self-heating, its chemistry has mostly been investigated on the trace scale only.

<span class="mw-page-title-main">Radiation</span> Waves or particles moving through space

In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes:

<span class="mw-page-title-main">Beta particle</span> Ionizing radiation

A beta particle, also called beta ray or beta radiation, is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β decay and β+ decay, which produce electrons and positrons respectively.

<span class="mw-page-title-main">Henri Becquerel</span> French physicist and engineer (1852–1908)

Antoine Henri Becquerel was a French engineer, physicist, Nobel laureate, and the first person to discover radioactivity. For work in this field he, along with Marie Skłodowska-Curie and Pierre Curie, received the 1903 Nobel Prize in Physics. The SI unit for radioactivity, the becquerel (Bq), is named after him.

<span class="mw-page-title-main">Curie (unit)</span> Non-SI unit of radioactivity

The curie is a non-SI unit of radioactivity originally defined in 1910. According to a notice in Nature at the time, it was to be named in honour of Pierre Curie, but was considered at least by some to be in honour of Marie Curie as well, and is in later literature considered to be named for both.

<span class="mw-page-title-main">Radioactive decay</span> Emissions from unstable atomic nuclei

Radioactive decay is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha, beta, and gamma decay. The weak force is the mechanism that is responsible for beta decay, while the other two are governed by the electromagnetism and nuclear force.

<span class="mw-page-title-main">Dosimetry</span> Measurement of absorbed ionizing radiation

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<span class="mw-page-title-main">Specific activity</span> Activity per unit mass of a radionuclide

In the context of radioactivity, activity or total activity (symbol A) is a physical quantity defined as the number of radioactive transformations per second that occur in a particular radionuclide. The unit of activity is the becquerel (symbol Bq), which is defined equivalent to reciprocal seconds (symbol s-1). The older, non-SI unit of activity is the curie (Ci), which is 3.7×1010 radioactive decay per second. Another unit of activity is the rutherford, which is defined as 1×106 radioactive decay per second.

<span class="mw-page-title-main">Health physics</span>

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MBQ, MBq, mBq, or mbq can refer to:


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