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The becquerel (English: /bɛkəˈrɛl/; symbol: Bq) is the SI derived unit of radioactivity. One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second. The becquerel is therefore equivalent to an inverse second, s⁻¹. The becquerel is named after Henri Becquerel, who shared a Nobel Prize in Physics with Pierre and Marie Curie in 1903 for their work in discovering radioactivity.^[2]

Capitalization

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.^[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 could be taken to mean 10⁶ disintegrations per second: 1·(10⁻⁶ s)⁻¹ = 10⁶ s⁻¹.^[4] 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.

Prefixes

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). 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 4,400 disintegrations per second or 4.4 kBq of activity.^[8] The global inventory of carbon-14 is estimated to be 7018850000000000000♠8.5×10¹⁸ Bq (8.5 EBq, 8.5 exabecquerel).^[9] The nuclear explosion in Hiroshima (An explosion of 16 kt or 67 TJ) is estimated to have produced 7024800000000000000♠8×10²⁴ Bq (8 YBq, 8 yottabecquerel).^[10]

Relationship to the curie

The becquerel succeeded the curie (Ci),^[11] 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]

Conversion factors:

1 Ci = 7010370000000000000♠3.7×10¹⁰ Bq = 37 GBq

1 μCi = 37,000 Bq = 37 kBq

1 Bq = 6999999000000000000♠2.7×10⁻¹¹ Ci = 6999999000000000000♠2.7×10⁻⁵ μCi

1 MBq = 0.027 mCi

Calculation of radioactivity

For a given mass m{displaystyle m} (in grams) of an isotope with atomic mass ma{displaystyle m_{a}} (in g/mol) and a half-life of t1/2{displaystyle t_{1/2}} (in s), the radioactivity can be calculated using:

ABq=mmaNAln⁡(2)t1/2{displaystyle A_{Bq}={frac {m}{m_{a}}}N_{A}{frac {ln(2)}{t_{1/2}}}}

With NA{displaystyle N_{A}} = 7023602214179000000♠6.02214179(30)×10²³ mol⁻¹, the Avogadro constant.

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

ABq=nNAln⁡(2)t1/2{displaystyle A_{Bq}=nN_{A}{frac {ln(2)}{t_{1/2}}}}

For instance, on average each gram of potassium contains 0.000117 gram of ⁴⁰K (all other naturally occurring isotopes are stable) that has a t1/2{displaystyle t_{1/2}} of 7016402990552000000♠1.277×10⁹ years = 7016403000000000000♠4.030×10¹⁶ s,^[12] and has an atomic mass of 39.964 g/mol,^[13] so the amount of radioactivity associated with a gram of potassium 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.

See also

• Background radiation


• Banana equivalent dose


• Counts per minute


• Ionizing radiation


• Orders of magnitude (radiation)


• Radiation poisoning


• Relative Biological Effectiveness


• Rem (unit)


• Rutherford (unit)


• 
  Sievert (biological dose equivalent of radiation)

References

External links

Look up becquerel in Wiktionary, the free dictionary.

• 
  Derived units on the International Bureau of Weights and Measures (BIPM) web site