The becquerel (symbol Bq) (pronounced: 'be-kə-rel) 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 and Marie Curie in 1903 for their work in discovering radioactivity.
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 could be taken to mean 106 disintegrations per second: 1·(10−6 s)−1 = 106 s−1. Other names considered were hertz (Hz), a special name already in use for the reciprocal second, and fourier (Fr). The hertz is now only used for periodic phenomena. Whereas 1 Hz is 1 cycle per second, 1 Bq is 1 aperiodic event per second.
This SI unit is named after Henri Becquerel. As with every International System of Units (SI) unit whose name is derived from the proper name of 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 capitalized material such as a title. 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. The global inventory of carbon-14 is estimated to be 8.5×1018 Bq (8.5 EBq, 8.5 exabecquerel). The nuclear explosion in Hiroshima (14 kt or 59 TJ) is estimated to have produced 8×1024 Bq (8 YBq, 8 yottabecquerel).
Relationship to the curie
- 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
With =6.022 141 79(30)×1023 mol−1, the Avogadro constant.
Since m/ma is the number of mols (n), the amount of radioactivity can be calculated by:
For instance, one gram of potassium contains 0.000117 gram of 40K (all other naturally occurring isotopes are stable) that has a of 1.277×109 years = 4.030×1016 s, and has an atomic mass of 39.964 g/mol, so the radioactivity is 30 Bq.
The following table shows radiation quantities in SI and non-SI units.
|Exposure (X)||roentgen||R||esu / 0.001293 g of air||1928|
|Absorbed dose (D)||erg•g−1||1950|
|Activity (A)||curie||Ci||3.7 × 1010 s−1||1953|
|Dose equivalent (H)||roentgen equivalent man||rem||100 erg•g−1||1971|
|Fluence (Φ)||(reciprocal area)||cm−2 or m−2||1962|
- Background radiation
- Banana equivalent dose
- Counts per minute
- Gray (unit)
- Hertz (equally defined unit, not used on radioactivity)
- Ionizing radiation
- Orders of magnitude (radiation)
- Rad (unit)
- Radiation poisoning
- Relative Biological Effectiveness
- Rem (unit)
- Roentgen (unit)
- Rutherford (unit)
- Sievert (biological dose equivalent of radiation)
- "BIPM - Becquerel". BIPM. Retrieved 2012-10-24.
- "BIPM - Table 3". 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
- 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
- "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.
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