Becquerel

Last updated
becquerel
Unit system SI
Unit of activity
SymbolBq
Named after Henri Becquerel
Conversions
1 Bq in ...... is equal to ...
    rutherford    10−6 Rd
    curie    2.703×10−11 Ci27 pCi
    SI base unit     s −1

The becquerel (English: /bɛkəˈrɛl/ ; symbol: Bq) is the unit of radioactivity in the International System of Units (SI). 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]

Contents

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 (in grams) of an isotope with atomic mass (in g/mol) and a half-life of (in s), the radioactivity can be calculated using:

With = 6.02214076×1023 mol−1, the Avogadro constant.

Since is the number of moles (), the amount of radioactivity can be calculated by:

For instance, on average each gram of potassium contains 117 micrograms of 40K (all other naturally occurring isotopes are stable) that has a 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, there is roughly 0.0169 g of potassium-40 present in a typical human body, decaying at a rate of approximately 4,430 decays per second. [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 injected 8×1024 Bq (8  YBq, 8 yottabecquerel) of radioactive fission products into the atmosphere. [13]

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), [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] [15]

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
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. [16]

Ionizing radiation related quantities view    talk    edit
QuantityUnitSymbolDerivationYear SI equivalence
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 x 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">Radon</span> Chemical element, symbol Rn and atomic number 86

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<span class="mw-page-title-main">Americium-241</span> Radioactive isotope of Americium

Americium-241 is an isotope of americium. Like all isotopes of americium, it is radioactive, with a half-life of 432.2 years. 241
Am
is the most common isotope of americium as well as the most prevalent isotope of americium in nuclear waste. It is commonly found in ionization type smoke detectors and is a potential fuel for long-lifetime radioisotope thermoelectric generators (RTGs). Its common parent nuclides are β from 241
Pu
, EC from 241
Cm
, and α from 245
Bk
. 241
Am
is fissile and the critical mass of a bare sphere is 57.6–75.6 kilograms (127.0–166.7 lb) and a sphere diameter of 19–21 centimetres (7.5–8.3 in). Americium-241 has a specific activity of 3.43 Ci/g (126.91 GBq/g). It is commonly found in the form of americium-241 dioxide. This isotope also has one meta state, 241m
Am
, with an excitation energy of 2.2 MeV (0.35 pJ) and a half-life of 1.23 μs. The presence of americium-241 in plutonium is determined by the original concentration of plutonium-241 and the sample age. Because of the low penetration of alpha radiation, americium-241 only poses a health risk when ingested or inhaled. Older samples of plutonium containing 241
Pu
contain a buildup of 241
Am
. A chemical removal of americium-241 from reworked plutonium may be required in some cases.

References

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