Becquerel
Encyclopedia
The becquerel 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 for Henri Becquerel
, who shared a Nobel Prize
with Pierre
and Marie Curie in 1903 for their work in discovering radioactivity.
In a fixed mass of radioactive material, the number of becquerels changes with time. Therefore, a sample radioactive decay rate is stated with a timestamp for short-lived isotopes, sometimes after adjustment to some specific date of interest (in the past or in the future). For example, one might quote a ten-day adjusted figure, that is, the amount of radioactivity that will still be present ten days in the future. This can de-emphasize short-lived isotopes. The average human body has 4400 becquerels from decaying potassium-40
, which is a naturally-occurring isotope of potassium.
SI
uses the becquerel rather than the second for the unit of activity measure to avoid dangerous mistakes: a measurement in becquerels is proportional to activity, and thus a more dangerous source of radiation gives a higher reading. A measurement in seconds is inversely proportional.
; 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 application, 1 Bq is a small unit; therefore, the prefixes are common. For example, natural potassium
(40K) in a typical human body produces 4,000 disintegrations per second, 4 kBq of activity. The nuclear explosion
in Hiroshima
(14 kt(TNT)) is estimated to have produced (8 YBq, 8 yottabecquerel).
" (cpm) is often used. Some radiation detectors are calibrated in "disintegrations per second" or "decays per second." All of these units can be converted to the absolute activity of the sample in Bq if one applies a number of significant conversions that take into account the radiation background, the detector efficiency, the counting geometry, the sample size, and the self-absorption of the radiation by the sample.
(Ci) is an older, non-SI unit of radioactivity equal to the activity of 1 gram of radium-226.
The conversion factors are:
(in grams) of an isotope with atomic mass
(in g/mol) and a half-life
of
(in s), the amount
of radioactivity can be calculated using:
With
=6.022 141 79(30) mol−1 the Avogadro constant.
For instance, one kilogram of potassium
contains 0.12 gram of 40K (all other isotopes are stable) that has a
of 1.248years=39.38388 seconds, and has
an atomic mass of 39.96399848 g/mol, so the radioactivity is 31.825 kBq.
SI derived unit
The International System of Units specifies a set of seven base units from which all other units of measurement are formed, by products of the powers of base units. These other units are called SI derived units, for example, the SI derived unit of area is square metre , and of density is...
of radioactivity
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...
. One Bq is defined as the activity of a quantity of radioactive material in which one nucleus
Atomic nucleus
The nucleus is the very dense region consisting of protons and neutrons at the center of an atom. It was discovered in 1911, as a result of Ernest Rutherford's interpretation of the famous 1909 Rutherford experiment performed by Hans Geiger and Ernest Marsden, under the direction of Rutherford. The...
decays per second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
. The Bq unit is therefore equivalent to an inverse second, s
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
−1. The becquerel is named for Henri Becquerel
Henri Becquerel
Antoine Henri Becquerel was a French physicist, Nobel laureate, and the discoverer of radioactivity along with Marie Curie and Pierre Curie, for which all three won the 1903 Nobel Prize in Physics.-Early life:...
, who shared a Nobel Prize
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
with Pierre
Pierre Curie
Pierre Curie was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity, and Nobel laureate. He was the son of Dr. Eugène Curie and Sophie-Claire Depouilly Curie ...
and Marie Curie in 1903 for their work in discovering radioactivity.
In a fixed mass of radioactive material, the number of becquerels changes with time. Therefore, a sample radioactive decay rate is stated with a timestamp for short-lived isotopes, sometimes after adjustment to some specific date of interest (in the past or in the future). For example, one might quote a ten-day adjusted figure, that is, the amount of radioactivity that will still be present ten days in the future. This can de-emphasize short-lived isotopes. The average human body has 4400 becquerels from decaying potassium-40
Potassium-40
Potassium-40 is a radioactive isotope of potassium which has a very long half-life of 1.248 years, or about 39.38 seconds.Potassium-40 is a rare example of an isotope which undergoes all three types of beta decay. About 89.28% of the time, it decays to calcium-40 with emission of a beta particle...
, which is a naturally-occurring isotope of potassium.
SI
International System of Units
The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...
uses the becquerel rather than the second for the unit of activity measure to avoid dangerous mistakes: a measurement in becquerels is proportional to activity, and thus a more dangerous source of radiation gives a higher reading. A measurement in seconds is inversely proportional.
Prefixes
As any SI unit, Bq can be prefixedSI prefix
The International System of Units specifies a set of unit prefixes known as SI prefixes or metric prefixes. An SI prefix is a name that precedes a basic unit of measure to indicate a decadic multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol...
; 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 application, 1 Bq is a small unit; therefore, the prefixes are common. For example, natural potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
(40K) in a typical human body produces 4,000 disintegrations per second, 4 kBq of activity. The nuclear explosion
Atomic bombings of Hiroshima and Nagasaki
During the final stages of World War II in 1945, the United States conducted two atomic bombings against the cities of Hiroshima and Nagasaki in Japan, the first on August 6, 1945, and the second on August 9, 1945. These two events are the only use of nuclear weapons in war to date.For six months...
in Hiroshima
Hiroshima
is the capital of Hiroshima Prefecture, and the largest city in the Chūgoku region of western Honshu, the largest island of Japan. It became best known as the first city in history to be destroyed by a nuclear weapon when the United States Army Air Forces dropped an atomic bomb on it at 8:15 A.M...
(14 kt(TNT)) is estimated to have produced (8 YBq, 8 yottabecquerel).
Bq versus counts per second
When measuring radioactivity of a sample with a detector, a unit of "counts per second" (cps) or "counts per minuteCounts per minute
Counts per minute is a measure of radioactivity. It is the number of atoms in a given quantity of radioactive material that are detected to have decayed in one minute. Disintegrations per minute is also a measure of radioactivity. It is the number of atoms in a given quantity of radioactive...
" (cpm) is often used. Some radiation detectors are calibrated in "disintegrations per second" or "decays per second." All of these units can be converted to the absolute activity of the sample in Bq if one applies a number of significant conversions that take into account the radiation background, the detector efficiency, the counting geometry, the sample size, and the self-absorption of the radiation by the sample.
Relationship to the curie
The curieCurie
The curie is a unit of radioactivity, defined asThis is roughly the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie, for whom the unit was named. In addition to the curie, activity can be measured using an SI derived unit,...
(Ci) is an older, non-SI unit of radioactivity equal to the activity of 1 gram of radium-226.
The conversion factors are:
- 1 Ci = 3.7×1010 Bq
- 1 Ci = 37 GBq
- 1 μCi = 37,000 Bq
- 1 Bq = 2.70×10−11 Ci
- 1 Bq = 2.70×10−5 μCi
- 1 GBq = 0.0270 Ci
Calculation of radioactivity
For a given mass (in grams) of an isotope with atomic massAtomic mass
The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....
(in g/mol) and a half-lifeHalf-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of
(in s), the amountof radioactivity can be calculated using:
- radioactivity(in Bq) =
With
=6.022 141 79(30) mol−1 the Avogadro constant.For instance, one kilogram of potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
contains 0.12 gram of 40K (all other isotopes are stable) that has a
of 1.248years=39.38388 seconds, and hasan atomic mass of 39.96399848 g/mol, so the radioactivity is 31.825 kBq.
See also
- SievertSievertThe sievert is the International System of Units SI derived unit of dose equivalent radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation as opposed to just the absorbed dose of radiation energy, which is measured in gray...
(biological dose equivalent of radiation). - Counts per minuteCounts per minuteCounts per minute is a measure of radioactivity. It is the number of atoms in a given quantity of radioactive material that are detected to have decayed in one minute. Disintegrations per minute is also a measure of radioactivity. It is the number of atoms in a given quantity of radioactive...
- Ionizing radiation unitsIonizing radiation unitsIonizing radiation units are standards for measuring ionizing radiation, including units for measuring the activity of radioactive sources, and for quantifying the amount of radiation striking other objects, particularly people...
- Curie (unit)CurieThe curie is a unit of radioactivity, defined asThis is roughly the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Marie and Pierre Curie, for whom the unit was named. In addition to the curie, activity can be measured using an SI derived unit,...
- Gray (unit)Gray (unit)The gray is the SI unit of absorbed radiation dose of ionizing radiation , and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter ....
- Ionizing radiation level examples - Example exposure scenarios
- Rad (unit)Rad (unit)The rad is a unit of absorbed radiation dose. The rad was first proposed in 1918 as "that quantity of X rays which when absorbed will cause the destruction of the malignant mammalian cells in question..." It was defined in CGS units in 1953 as the dose causing 100 ergs of energy to be absorbed by...
- Rem (unit)
- Roentgen (unit)
- Rutherford (unit)Rutherford (unit)The rutherford is an obsolete unit of radioactivity, defined as the activity of a quantity of radioactive material in which one million nuclei decay per second. It is therefore equivalent to one megabecquerel. It was named after Ernest Rutherford. It is not an SI unit....
- Background radiationBackground radiationBackground radiation is the ionizing radiation constantly present in the natural environment of the Earth, which is emitted by natural and artificial sources.-Overview:Both Natural and human-made background radiation varies by location....
- Relative Biological EffectivenessRelative biological effectivenessIn radiology, the relative biological effectiveness is a number that expresses the relative amount of damage that a fixed amount of ionizing radiation of a given type can inflict on biological tissues...
- Radiation poisoningRadiation poisoningAcute radiation syndrome also known as radiation poisoning, radiation sickness or radiation toxicity, is a constellation of health effects which occur within several months of exposure to high amounts of ionizing radiation...
- Orders of magnitude (radiation)Orders of magnitude (radiation)Recognized effects of higher acute radiation doses are described in more detail in the article on radiation poisoning. Although the International System of Units defines the sievert as the unit of radiation dose equivalent, chronic radiation levels and standards are still often given in unts of...
- Banana equivalent doseBanana equivalent doseA banana equivalent dose is a whimsical unit of radiation exposure, informally defined as the additional dose a person will absorb from eating one banana...
External links
- Derived units on the International Bureau of Weights and MeasuresInternational Bureau of Weights and MeasuresThe International Bureau of Weights and Measures , is an international standards organisation, one of three such organisations established to maintain the International System of Units under the terms of the Metre Convention...
(BIPM) web site