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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.
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).
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|
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