Becquerel

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"Bq" redirects here. For other uses, see BQ and Becquerel (disambiguation).
Becquerel
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: /ˈbɛkərɛl/ BEK-ə-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]

Definition[edit]

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 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.

Prefixes[edit]

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[edit]

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[edit]

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[edit]

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[edit]

References[edit]

  1. ^ "BIPM - Becquerel". BIPM. Retrieved 2012-10-24. 
  2. ^ a b "BIPM - Table 3". BIPM. Retrieved 2012-10-24. 
  3. ^ a b c 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 
  4. ^ Radioactive human body — Harvard University Natural Science Lecture Demonstrations - 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". Lund University. 1990-06-01. Retrieved 2014-01-12. 
  9. ^ "Atomic Weights and Isotopic Compositions for All Elements". NIST. Retrieved 2014-01-12. 

External links[edit]