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Title: Becquerel  
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Subject: Technetium, Pahute Mesa, Carbon-14, Effects of the Chernobyl disaster, Polonium
Collection: Si Derived Units, Units of Frequency, Units of Radioactivity
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Unit system SI derived unit
Unit of Radioactivity
Symbol Bq 
Named after Henri Becquerel
In SI base units s−1

The becquerel (symbol Bq) (pronounced: ) is the SI derived unit of radioactivity. One Bq is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. The Bq unit is therefore equivalent to an inverse second, s−1. The becquerel is named after Henri Becquerel, who shared a Nobel Prize with Pierre Curie and Marie Curie in 1903 for their work in discovering radioactivity.[1]


  • Definition 1
  • Prefixes 2
  • Relationship to the curie 3
  • Calculation of radioactivity 4
  • Radiation-related quantities 5
  • See also 6
  • References 7
  • External links 8


1 Bq = 1 s−1[2]

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 could be taken to mean 106 disintegrations per second: 1·(10−6 s)−1 = 106 s−1.[3] Other names considered were hertz (Hz), a special name already in use for the reciprocal second, and fourier (Fr).[3] The hertz is now only used for periodic phenomena.[2] Whereas 1 Hz is 1 cycle per second, 1 Bq is 1 aperiodic radioactivity event per second.

This SI unit is named after Henri Becquerel. As with every International System of Units (SI) unit named for a person, the first letter of its symbol is upper case (Bq). However, when an SI unit is spelled out in English, it should always begin with a lower case 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. Note that "degree Celsius" conforms to this rule because the "d" is lowercase.— Based on The International System of Units, section 5.2.


Like any SI unit, Bq can be prefixed; commonly used multiples are kBq (kilobecquerel, 103 Bq), MBq (megabecquerel, 106 Bq), GBq (gigabecquerel, 109 Bq), TBq (terabecquerel, 1012 Bq), and PBq (petabecquerel, 1015 Bq). For practical applications, 1 Bq is a small unit; therefore, the prefixes are common. For example, the roughly 0.0169 g of potassium-40 present in a typical human body produces approximately 266,000 disintegrations per minute, which equates to about 4,400 disintegrations per second or 4.4 kBq of activity.[4] The global inventory of carbon-14 is estimated to be 8.5×1018 Bq (8.5 EBq, 8.5 exabecquerel).[5] The nuclear explosion in Hiroshima (14 kt or 59 TJ) is estimated to have produced 8×1024 Bq (8 YBq, 8 yottabecquerel).[6]

Relationship to the curie

The becquerel succeeded the curie (Ci),[7] 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.[3]

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 GBq = 0.027 Ci

Calculation of radioactivity

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

A_{Bq} = \frac{m}{m_a}N_A\frac{\ln(2)}{t_{1/2}}

With N_A=6.022 141 79(30)×1023 mol−1, the Avogadro constant.

Since m/ma is the number of mols (n), the amount of radioactivity A can be calculated by:

A_{Bq} = nN_A\frac{\ln(2)}{t_{1/2}}

For instance, one 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,[8] and has an atomic mass of 39.964 g/mol,[9] so the radioactivity is 30 Bq.

Radiation-related quantities

Graphic showing relationships between radioactivity and detected ionizing radiation

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

Quantity Name Symbol Unit Year
Exposure (X) roentgen R esu / 0.001293 g of air 1928
Absorbed dose (D) erg·g−1 1950
rad rad 100 erg·g−1 1953
gray Gy J·kg−1 1974
Activity (A) curie Ci 3.7 × 1010 s−1 1953
becquerel Bq s−1 1974
Dose equivalent (H) roentgen equivalent man rem 100 erg·g−1 1971
sievert Sv J·kg−1 1977
Fluence (Φ) (reciprocal area) cm−2 or m−2 1962

See also


  1. ^ "BIPM - Becquerel".  
  2. ^ a b "BIPM - Table 3".  
  3. ^ a b c Allisy, A. (1995), "From the curie to the becquerel", Metrologia 32 (6): 467–479,  
  4. ^ — Harvard University Natural Science Lecture DemonstrationsRadioactive human body - Accessed October 2013
  5. ^ G.R. Choppin, J.O.Liljenzin, J. Rydberg, "Radiochemistry and Nuclear Chemistry", 3rd edition, Butterworth-Heinemann, 2002. ISBN 978-0-7506-7463-8.
  6. ^ Michael J. Kennish, Pollution Impacts on Marine Biotic Communities , CRC Press, 1998, p. 74. ISBN 978-0-8493-8428-8.
  7. ^ It was adopted by the BIPM in 1975, see resolution 8 of the 15th CGPM meeting
  8. ^ "Table of Isotopes decay data".  
  9. ^ "Atomic Weights and Isotopic Compositions for All Elements".  

External links

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