Röntgen
Encyclopedia
The roentgen is a unit of measurement for exposure to ionizing radiation
(such as X-ray
and gamma ray
s), and is named after the German
physicist Wilhelm Röntgen. Adopted in 1928, 1 R is the amount of radiation required to liberate positive and negative charge
s of one electrostatic unit of charge
(esu or StatCoulomb) in one cubic centimeter of dry air at standard temperature and pressure (STP). This corresponds to the generation of approximately 2.0819×109 ion
pairs.
The unit is of a family of variant metric radiation units used largely in the United States
. Related units are the rad
, a measure of absorbed dose
, and the rem, a unit of equivalent dose
which adjusts for the impacts of different forms of radiation on biological matter.
units, 1 R = 2.58×10−4 C/kg
(from 1 esu ≈ 3.33564 C and the standard atmosphere air density of ~1.293 kg/m³).
Until 2006, a different roentgen was (confusingly) accepted for use with the SI system, with its value expressed in terms of the SI units charge
divided by unit mass (coulomb/kg
) rather than as in the original definition (statC/cm³). Although its use was allowable under the SI system, it is not itself an SI unit and its continued use is "strongly discouraged" by the National Institute of Standards and Technology
style guide for NIST authors.
The typical exposure to normal background radiation
for a human being is about 200 milliroentgens per year, or about 23 microroentgens per hour.
In human tissue, one Roentgen of gamma radiation exposure results in about one rad of absorbed dose (= 0.01 Gy).
When measuring dose absorbed in man due to exposure, units of absorbed dose
are used (the related rad
or SI gray
), or, with consideration of biological effects from differing radiation types, units of equivalent dose
, such as the related rem or the SI sievert
.
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
(such as X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
and gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s), and is named after the German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
physicist Wilhelm Röntgen. Adopted in 1928, 1 R is the amount of radiation required to liberate positive and negative charge
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
s of one electrostatic unit of charge
Statcoulomb
The statcoulomb or franklin or electrostatic unit of charge is the physical unit for electrical charge used in the centimetre-gram-second system of units and Gaussian units. It is a derived unit given by...
(esu or StatCoulomb) in one cubic centimeter of dry air at standard temperature and pressure (STP). This corresponds to the generation of approximately 2.0819×109 ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
pairs.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. Related units are the rad
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...
, a measure of absorbed dose
Absorbed dose
Absorbed dose is a measure of the energy deposited in a medium by ionizing radiation per unit mass...
, and the rem, a unit of equivalent dose
Equivalent dose
The equivalent absorbed radiation dose, usually shortened to equivalent dose, is a computed average measure of the radiation absorbed by a fixed mass of biological tissue, that attempts to account for the different biological damage potential of different types of ionizing radiation...
which adjusts for the impacts of different forms of radiation on biological matter.
Conversion
In SIInternational 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...
units, 1 R = 2.58×10−4 C/kg
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
(from 1 esu ≈ 3.33564 C and the standard atmosphere air density of ~1.293 kg/m³).
Until 2006, a different roentgen was (confusingly) accepted for use with the SI system, with its value expressed in terms of the SI units charge
Charge (physics)
In physics, a charge may refer to one of many different quantities, such as the electric charge in electromagnetism or the color charge in quantum chromodynamics. Charges are associated with conserved quantum numbers.-Formal definition:...
divided by unit mass (coulomb/kg
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
) rather than as in the original definition (statC/cm³). Although its use was allowable under the SI system, it is not itself an SI unit and its continued use is "strongly discouraged" by the National Institute of Standards and Technology
National Institute of Standards and Technology
The National Institute of Standards and Technology , known between 1901 and 1988 as the National Bureau of Standards , is a measurement standards laboratory, otherwise known as a National Metrological Institute , which is a non-regulatory agency of the United States Department of Commerce...
style guide for NIST authors.
Exposure
An exposure of 500 roentgens in five hours is usually lethal for human beings.The typical exposure to normal background radiation
Background radiation
Background 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....
for a human being is about 200 milliroentgens per year, or about 23 microroentgens per hour.
In human tissue, one Roentgen of gamma radiation exposure results in about one rad of absorbed dose (= 0.01 Gy).
When measuring dose absorbed in man due to exposure, units of absorbed dose
Absorbed dose
Absorbed dose is a measure of the energy deposited in a medium by ionizing radiation per unit mass...
are used (the related rad
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...
or SI gray
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 ....
), or, with consideration of biological effects from differing radiation types, units of equivalent dose
Equivalent dose
The equivalent absorbed radiation dose, usually shortened to equivalent dose, is a computed average measure of the radiation absorbed by a fixed mass of biological tissue, that attempts to account for the different biological damage potential of different types of ionizing radiation...
, such as the related rem or the SI sievert
Sievert
The 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...
.
See also
- Wilhelm Conrad RöntgenWilhelm Conrad RöntgenWilhelm Conrad Röntgen was a German physicist, who, on 8 November 1895, produced and detected electromagnetic radiation in a wavelength range today known as X-rays or Röntgen rays, an achievement that earned him the first Nobel Prize in Physics in 1901....
- 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...
— c.g.s. unit of absorbed dose - 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 ....
— SI unit of absorbed dose - Roentgen equivalent man, or rem, a unit of radiation dose equivalent
- 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...
— The sievert (symbol: Sv) is the SI derived unit of dose equivalent. - MicrodoseMicrodoseMicrodose refers to a category of radiology modalities providing a very low radiation dose. These modalities are typically based on a photon-counting detector for capturing the image.-Photon-counting Detector:...
- 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...