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The becquerel (symbol Bq) is the SI derived unit
SI derived unit

SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
 of radioactivity
Radioactive decay

Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide....
. 1 Bq is defined as the activity of a quantity of radioactive material in which one nucleus
Atomic nucleus

The nucleus of an atom is the very dense region, consisting of nucleons , at the center of an atom. Although the size of the nucleus varies considerably according to the mass of the atom, the size of the entire atom is comparatively constant....
 decays per second
Second

The second , sometimes abbreviated sec., is the name of a units of measurement of time, and is the International System of Units SI base unit of time....
. It is therefore equivalent to s
Second

The second , sometimes abbreviated sec., is the name of a units of measurement of time, and is the International System of Units SI base unit of time....
-1. The becquerel is named for Henri Becquerel
Henri Becquerel

Antoine Henri Becquerel was a France physicist, Nobel laureate, and one of the discoverers of radioactivity. He won the 1903 Nobel Prize in Physics for discovering radioactivity....
, who shared a Nobel Prize
Nobel Prize

The Nobel Prize , established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Nobel Prize in Physics, Nobel Prize in Chemistry, Nobel Prize in Physiology or Medicine, Nobel Prize in Literature, and Nobel Peace Prize in 1901....
 with Pierre
Pierre Curie

Pierre Curie was a French Physics, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity, and Nobel laureate. In 1903 he received the Nobel Prize in Physics with his wife, Marie Curie, and Henri Becquerel, "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phe...
 and Marie Curie for their work in discovering radioactivity.

In a fixed mass of radioactive material, the number of becquerels changes with time.






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The becquerel (symbol Bq) is the SI derived unit
SI derived unit

SI derived units are part of the SI system of measurement Units of measurements and are derived from the seven SI base units.Note that while the names of all SI units are in lowercase, the symbols of units named after people are written with an initial capital letter ....
 of radioactivity
Radioactive decay

Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide....
. 1 Bq is defined as the activity of a quantity of radioactive material in which one nucleus
Atomic nucleus

The nucleus of an atom is the very dense region, consisting of nucleons , at the center of an atom. Although the size of the nucleus varies considerably according to the mass of the atom, the size of the entire atom is comparatively constant....
 decays per second
Second

The second , sometimes abbreviated sec., is the name of a units of measurement of time, and is the International System of Units SI base unit of time....
. It is therefore equivalent to s
Second

The second , sometimes abbreviated sec., is the name of a units of measurement of time, and is the International System of Units SI base unit of time....
-1. The becquerel is named for Henri Becquerel
Henri Becquerel

Antoine Henri Becquerel was a France physicist, Nobel laureate, and one of the discoverers of radioactivity. He won the 1903 Nobel Prize in Physics for discovering radioactivity....
, who shared a Nobel Prize
Nobel Prize

The Nobel Prize , established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Nobel Prize in Physics, Nobel Prize in Chemistry, Nobel Prize in Physiology or Medicine, Nobel Prize in Literature, and Nobel Peace Prize in 1901....
 with Pierre
Pierre Curie

Pierre Curie was a French Physics, a pioneer in crystallography, magnetism, piezoelectricity and radioactivity, and Nobel laureate. In 1903 he received the Nobel Prize in Physics with his wife, Marie Curie, and Henri Becquerel, "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phe...
 and Marie Curie 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 always 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.

SI
International System of Units

The International System of Units is the modern form of the metric system and is generally a system devised around the convenience of the number ten....
 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. As any SI unit, Bq can be prefixed
SI prefix

An SI prefix is a name or associated symbol that precedes a basic unit of measure to form a decimal multiple . The abbreviation SI is from the French language name Syst?me International d?Unit?s ....
; 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).

When measuring radioactivity of a sample with a detector, a unit of "counts per second" (cps) or "counts per minute
Counts 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....
" (cpm) are often used. These units can be converted to the absolute activity of the sample in Bq if one applies a number of significant conversions, e.g., for the radiation background, for the detector efficiency, for the counting geometry, for self-absorption of the radiation in the sample.

The becquerel can be used for the frequency of aperiodic or stochastic events; for periodic events, the hertz
Hertz

The hertz is a measure of frequency per unit of time, or the number of list of cycles per second. It is the SI base unit of frequency in the International System of Units , and is used worldwide in both general-purpose and scientific contexts....
, which is also defined as s–1, is used as unit.

Relationship to the curie

The curie
Curie

The curie is a unit of Radioactive decay, defined asThis is roughly the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Marie Curie and Pierre Curie....
 (Ci) is an older, non-SI unit of radioactivity.

The conversion factors are:

1 Ci = 3.7×1010 Bq


and

1 Bq = 2.70×10-11 Ci


Definition

1 Bq = 1 s–1

External links

  • on the BIPM web site