Definition of roentgen in US English:


(also R)


  • A unit of ionizing radiation, the amount producing one electrostatic unit of positive or negative ionic charge in one cubic centimeter of air under standard conditions.

    • ‘A lethal exposure of radiation ranges from 300 to 500 roentgens an hour; levels in the tour areas vary from 15 to several hundred microroentgens an hour.’
    • ‘Some paramecium can withstand 200,000 roentgens.’
    • ‘This is also equivalent to exposure to a level of one roentgen.’
    • ‘She talked about rems and rads and roentgens per hour, and at first, he tried to memorize her words, but he wasn't able to commit the information to memory.’


1920s: named after Wilhelm Conrad Röntgen (1845–1923), German physicist, discoverer of X-rays.