A special name was introduced for thereciprocal second (s−1) to represent radioactivity to avoid potentially dangerous mistakes with prefixes. For example, 1 μs−1 would mean 106 disintegrations per second:(10−6 s)−1 =106 s−1,[4] whereas 1 μBq would mean 1 disintegration per 1 million seconds:10–6 s–1. Other names considered werehertz (Hz), a special name already in use for the reciprocal second (forperiodic events of any kind), and fourier (Fr; afterJoseph Fourier).[4] The hertz is now only used for periodic phenomena.[5] While 1 Hz replaces the deprecated termcycle per second, 1 Bq refers to one event per second on average foraperiodic radioactive decays.
Thegray (Gy) and the becquerel (Bq) were introduced in 1975.[6] Between 1953 and 1975, absorbed dose was often measured with therad. Decay activity was given with thecurie before 1946 and often with therutherford between 1946[7] and 1975.
As with every International System of Units (SI) unit named after 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 usingtitle case.[8]
Like any SI unit, Bq can beprefixed; commonly used multiples are kBq (kilobecquerel,103 Bq), MBq (megabecquerel,106 Bq, equivalent to 1rutherford), GBq (gigabecquerel,109 Bq), TBq (terabecquerel,1012 Bq), and PBq (petabecquerel,1015 Bq). Large prefixes are common for practical uses of the unit.
For practical applications, 1 Bq is a small unit. For example, there is roughly 0.017 g ofpotassium-40 in a typical human body, producing about 4,400 decays per second (Bq).[9]
These examples are useful for comparing the amount of activity of these radioactive materials, but should not be confused with the amount of exposure toionizing radiation that these materials represent. The level of exposure and thus theabsorbed dose received are what should be considered when assessing the effects of ionizing radiation on humans.
Relation between some ionizing radiation units[12]
The becquerel succeeded thecurie (Ci),[13] an older, non-SI unit of radioactivity based on the activity of 1 gram ofradium-226. The curie is defined as3.7×1010 s−1, or 37 GBq.[4][14]
Graphic showing relationships between radioactivity and detected ionizing radiation
The following table shows radiation quantities in SI and non-SI units.WR (formerly 'Q' factor) is a factor that scales the biological effect for different types of radiation, relative to x-rays (e.g. 1 for beta radiation, 20 for alpha radiation, and a complicated function of energy for neutrons). In general, conversion between rates of emission, the density of radiation, the fraction absorbed, and the biological effects, requires knowledge of the geometry between source and target, the energy and the type of the radiation emitted, among other factors.[15][not specific enough to verify]
^"BIPM - Table 3".BIPM. Retrieved2015-07-19.(d) The hertz (one per second) is usedonly for periodic phenomena, and the becquerel (also one per second) is usedonly for stochastic processes in activity referred to a radionuclide.
^Harder, D (1976), "[The new radiologic units of measurement gray and becquerel (author's translation from the German original)]",Röntgen-Blätter,29 (1):49–52,PMID1251122.
