Roentgen (unit)
Roentgen | |
---|---|
General information | |
Unit system | Legacy unit |
Unit of | Exposure to ionizing radiation |
Symbol | R |
Named after | Wilhelm Röntgen |
Conversions | |
1 R in ... | ... is equal to ... |
SI base units | 2.58×10−4 A⋅s/kg |
The roentgen or röntgen (/ˈrɛntɡən, -dʒən, ˈrʌnt-/;[2] symbol R) is a legacy unit of measurement for the exposure of X-rays and gamma rays, and is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air (statcoulomb per kilogram). In 1928, it was adopted as the first international measurement quantity for
, who discovered X-rays and was awarded the first Nobel Prize in Physics for the discovery.However, although this was a major step forward in standardising radiation measurement, the roentgen has the disadvantage that it is only a measure of air ionisation, and not a direct measure of radiation absorption in other materials, such as different forms of
As the science of radiation dosimetry developed, it was realised that the ionising effect, and hence tissue damage, was linked to the energy absorbed, not just radiation exposure. Consequently new radiometric units for radiation protection were defined which took this into account. In 1953 the International Commission on Radiation Units and Measurements (ICRU) recommended the rad, equal to 100 erg/g, as the unit of measure of the new radiation quantity absorbed dose. The rad was expressed in coherent cgs units.[5] In 1975 the unit
The roentgen has been redefined over the years. It was last defined by the U.S.'s National Institute of Standards and Technology (NIST) in 1998 as 2.58×10−4 C/kg, with a recommendation that the definition be given in every document where the roentgen is used.[6]
History
The roentgen has its roots in the
1 esu/cm3 × 3.33564 × 10−10 C/esu × 1,000,000 cm3/m3 ÷ 1.293 kg/m3 = 2.58 × 10−4 C/kg
This definition was used under different names (e, R, and German unit of radiation) for the next 20 years. In the meantime, the French Roentgen was given a different definition which amounted to 0.444 German R.
ICR definitions
In 1928, the International Congress of Radiology (ICR) defined the roentgen as "the quantity of X-radiation which, when the secondary electrons are fully utilised and the wall effect of the chamber is avoided, produce in 1 cc of atmospheric air at 0 °C and 76 cm of mercury pressure such a degree of conductivity that 1 esu of charge is measured at saturation current."[7] The stated 1 cc of air would have a mass of 1.293 mg at the conditions given, so in 1937 the ICR rewrote this definition in terms of this mass of air instead of volume, temperature and pressure.[9] The 1937 definition was also extended to gamma rays, but later capped at 3 MeV in 1950.
GOST definition
The
ICRP definition
The introduction of the roentgen measurement unit, which relied upon measuring the ionisation of air, replaced earlier less accurate practices that relied on timed exposure, film exposure, or fluorescence.
The International Commission on Radiation Units and Measurements (ICRU) took over the definition of the roentgen in 1950, defining it as "the quantity of X or γ-radiation such that the associated corpuscular emission per 0.001293 gram of air produces, in air, ions carrying 1 electrostatic unit of quantity of electricity of either sign."[15] The 3 MeV cap was no longer part of the definition, but the degraded usefulness of this unit at high beam energies was mentioned in the accompanying text. In the meantime, the new concept of roentgen equivalent man (rem) had been developed.
Starting in 1957, the ICRP began to publish their recommendations in terms of rem, and the roentgen fell into disuse. The medical imaging community still has a need for ionization measurements, but they gradually converted to using C/kg as legacy equipment was replaced.[16] The ICRU recommended redefining the roentgen to be exactly 2.58 × 10−4 C/kg in 1971.[17]
European Union
In 1971 the
NIST definition
Today the roentgen is rarely used, and the
Development of replacement radiometric quantities
Although a convenient quantity to measure with an air ion chamber, the roentgen had the disadvantage that it was not a direct measure of either the intensity of X-rays or their absorption, but rather was a measurement of the ionising effect of X-rays in a specific circumstance; which was dry air at 0
Because of this the roentgen had a variable relationship to the amount of energy absorbed dose per unit mass in the target material, as different materials have different absorption characteristics. As the science of radiation dosimetry developed, this was seen as a serious shortcoming.
In 1940,
In the late 1950s the
When measuring
The following table shows radiation quantities in SI and non-SI units:
Quantity | Unit | Symbol | Derivation | Year | SI equivalent |
---|---|---|---|---|---|
Activity (A) | becquerel | Bq | s−1 | 1974 | SI unit |
curie | Ci | 3.7 × 1010 s−1 | 1953 | 3.7×1010 Bq | |
rutherford | Rd | 106 s−1 | 1946 | 1,000,000 Bq | |
Exposure (X) | coulomb per kilogram | C/kg | C⋅kg−1 of air | 1974 | SI unit |
röntgen | R | esu / 0.001293 g of air | 1928 | 2.58 × 10−4 C/kg | |
Absorbed dose (D) | gray | Gy | J⋅kg−1 | 1974 | SI unit |
erg per gram | erg/g | erg⋅g−1 | 1950 | 1.0 × 10−4 Gy | |
rad
|
rad | 100 erg⋅g−1 | 1953 | 0.010 Gy | |
Equivalent dose (H) | sievert | Sv | J⋅kg−1 × WR | 1977 | SI unit |
röntgen equivalent man | rem | 100 erg⋅g−1 × WR | 1971 | 0.010 Sv | |
Effective dose (E) | sievert | Sv | J⋅kg−1 × WR × WT | 1977 | SI unit |
röntgen equivalent man | rem | 100 erg⋅g−1 × WR × WT | 1971 | 0.010 Sv |
See also
- Gray (unit) – SI unit of absorbed dose
- Orders of magnitude (radiation)
- Rad (unit)– cgs unit of absorbed dose
- Roentgen equivalent man, or rem – a unit of radiation dose equivalent
- Sievert (symbol: Sv) – the SI derived unit of dose equivalent
- Wilhelm Röntgen
References
- ^ Frame, Paul (2007-07-25). "Pocket Chambers and Pocket Dosimeters". Health physics historical instrument museum collection. Oak Ridge Associated Universities. Retrieved 2021-10-07.
- ^ "Röntgen". Random House Webster's Unabridged Dictionary.
- ^ a b "Princeton Radiation Safety Guide, Appendix E: Roentgens, RADs, REMs, and other Units". Archived from the original on 2015-02-22. Retrieved 10 May 2012.
- ^ Sprawls, Perry. "Radiation Quantities and Units". The Physical Principles of Medical Imaging, 2nd Ed. Retrieved 10 May 2012.
- LCCN 60014734. Retrieved 2012-05-15.
- ^ a b Hebner, Robert E. (1998-07-28). "Metric System of Measurement: Interpretation of the International System of Units for the United States" (PDF). Federal Register. 63 (144). US Office of the Federal Register: 40339. Retrieved 9 May 2012.
- ^ a b Van Loon, R.; and Van Tiggelen, R., Radiation Dosimetry in Medical Exposure: A Short Historical Overview Archived 2007-10-24 at the Wayback Machine, 2004>
- ^ "Instruments de mesure à lecture directe pour les rayons x. Substitution de la méthode électrométrique aux autres méthodes de mesure en radiologie. Scleromètre et quantimètre". Archives d'électricité médicale. 16. Bordeaux: 692–699. 1908.
- LCCN 60-14734. Retrieved 15 May 2012.
- S2CID 95827816.
- ^ Cantrill MD, S.T.; Parker, H.M. (1945-01-05). The Tolerance Dose (Report). US Atomic Energy Commission, Argonne National Laboratory. Archived from the original on April 7, 2021. Retrieved 14 May 2012.
- ^ Mutscheller, A. (1925). Physical standards of protection against Roentgen ray dangers, AJR. American Journal of Roentgenology, 13, 65–69.
- ^ Meinhold, Charles B. (April 1996). One Hundred Years of X Rays and Radioactivity – Radiation Protection: Then and Now (PDF). International Congress. Vienna, Austria: International Radiation Protection Association. Retrieved 14 May 2012.
- S2CID 71278114. Retrieved 12 May 2012.
- ^ Recommendations of the International Commission on Radiological Protection and of the International Commission on Radiological Units (PDF). National Bureau of Standards Handbook. Vol. 47. US Department of Commerce. 1950. Retrieved 14 November 2012.
- ISBN 978-1-4390-5872-5. Retrieved 12 May 2012.
- ^ ICRU Report 19, 1971
- ^ "Council Directive 71/354/EEC: On the approximation of the laws of the Member States relating to units of measurement". The Council of the European Communities. 18 October 1971. Retrieved 19 May 2012.
- ^ The Council of the European Communities (1979-12-21). "Council Directive 80/181/EEC of 20 December 1979 on the approximation of the laws of the Member States relating to Unit of measurement and on the repeal of Directive 71/354/EEC". Retrieved 19 May 2012.
- ^ International Bureau of Weights and Measures (1977). United States National Bureau of Standards (ed.). The international system of units (SI). NBS Special Publication 330. Dept. of Commerce, National Bureau of Standards. p. 12. Retrieved 18 May 2012.
- ISBN 92-822-2213-6, archived(PDF) from the original on 2021-06-04, retrieved 2021-12-16
- ^ Lyons, John W. (1990-12-20). "Metric System of Measurement: Interpretation of the International System of Units for the United States". Federal Register. 55 (245). US Office of the Federal Register: 52242–52245.
- ^ Thompson, Ambler; Taylor, Barry N. (2008). Guide for the Use of the International System of Units (SI) (2008 ed.). Gaithersburg, MD: National Institute of Standards and Technology. p. 10. SP811. Archived from the original on 16 May 2008. Retrieved 28 November 2012.
- ISBN 0-521-22436-5. Retrieved 2012-05-15.
- ISBN 978-3-642-00737-8. Retrieved 2012-05-14.
- ^ Guill, JH; Moteff, John (June 1960). "Dosimetry in Europe and the USSR". Third Pacific Area Meeting Papers — Materials in Nuclear Applications. Symposium on Radiation Effects and Dosimetry - Third Pacific Area Meeting American Society for Testing Materials, October 1959, San Francisco, 12–16 October 1959. American Society Technical Publication. 276. ASTM International. p. 64. LCCN 60014734. Retrieved 2012-05-15.
- ^ "CCU: Consultative Committee for Units". International Bureau of Weights and Measures (BIPM). Retrieved 2012-05-18.
- ISBN 0-7668-1113-1.
- ISBN 0-521-22436-5. Retrieved 2012-05-15.
External links
- NIST: Units outside the SI
- Radiation Dose Units – Health Physics Society