Röntgen 155840 226030587 2008-07-16T14:51:28Z 98.227.182.153 {{for|Röntgen radiation|X-ray}} :'' For other uses of '''röntgen''' or '''roentgen''''', see [[Roentgen]] The '''röntgen''' or '''roentgen''' (symbol '''R''') is a unit of measurement for [[ionizing radiation]] (such as [[X-ray]] and [[gamma ray]]s), and is named after the [[Germany|German]] physicist [[Wilhelm Röntgen]]. 1 R is the amount of radiation required to liberate positive and negative charges of one [[Statcoulomb|electrostatic unit]] of [[electric charge|charge]] in 1 [[cubic centimeter|cm³]] of air at [[standard temperature and pressure]] (STP). This corresponds to the generation of approximately 2.08&times;10<sup>9</sup> [[ion]] pairs. The röntgen is accepted for use with the SI system but in this case its value is expressed in terms of the SI units [[Charge (physics)|charge]] divided by unit mass ([[coulomb|C]]/[[kilogram|kg]]) rather than as in the original definition. Although its use is allowable under the SI system, it is not itself an SI unit and continued use is "strongly discouraged" by the [[National Institute of Standards and Technology]].<ref name="NIST"> Taylor, BN, "[http://physics.nist.gov/Pubs/SP811/sec05.html#5.2 Units temporarily accepted for use with the SI]", ''NIST Guide for the Use of the International System of Units (SI)'', chapter 5, Physics Laboratory Publications, April 1995, retrieved and archived [http://www.webcitation.org/5YWY1pd2K] 12th June 2008</ref> == Explanation == The röntgen was occasionally used to measure exposure to radiation in other forms than X-rays or gamma rays. To adjust for the different impact of different forms of radiation on biological matter, "[[röntgen equivalent man]]" or '''rem''' was also in use. Exposure in rems is equal to the exposure in röntgens multiplied by the ''Q value'', a constant describing the type of radiation. The rem is now superseded by the [[sievert]] (see the latter for a list of ''Q'' values). ==Conversion== In [[International System of Units|SI]] units, 1 R = 2.58&times;10<sup>&minus;4</sup> [[coulomb|C]]/[[kilogram|kg]] (from 1 esu ≈ 3.33564{{e|&minus;10}} C and a standard atmosphere has an air density ~1.293 kg/m³).<ref name="NIST" /> ==Dosage== On this scale a dose of about 500 R in 5 [[hours]] is lethal for humans. A typical dose of normal background radiation for a human is 200 mR per year. ==See also== * [[Wilhelm Conrad Röntgen]] * [[rad (unit)]] - another unit of radiation dose. * [[Gray (unit)]] - more popular unit of radiation dose. ==References== {{reflist}} ==External links== *[http://physics.nist.gov/cuu/Units/outside.html NIST: Units outside the SI] {{DEFAULTSORT:Roentgen}} [[Category:Units of radiation dose]] [[Category:Non-SI metric units]] [[de:Röntgen (Einheit)]] [[et:Röntgen]] [[es:Roentgen (unidad)]] [[fr:Röntgen]] [[id:Röntgen]] [[it:Röntgen]] [[he:רנטגן (יחידה)]] [[nl:Röntgen (eenheid)]] [[ja:レントゲン (単位)]] [[pl:Rentgen]] [[ro:Röntgen]] [[ru:Рентген (единица измерения)]] [[sk:Röntgen]] [[tr:Röntgen (birim)]] [[uk:Рентген (одиниця)]] [[zh:倫琴 (單位)]]