Unit of x-radiation or gamma radiation
Or röntgen; Unit (symbol r) of radiation exposure, used for X-rays and gamma rays. It is defined in terms of the number of ions produced in one cubic centimeter of air by the radiation. Exposure to 1,000 roentgens gives rise to an absorbed dose of about 870 rads (8.7 grays), which is a dose equivalent of 870 rems (8.7 sieverts).
A unit of gamma radiation measured by the amount of ionization in air. In non-bony biological tissue 1 roentgen delivers a dose approximately equal to 1 rad.
A unit of radiation exposure; the dose of ionizing radiation that will produce 1 electrostatic unit of electricity in 1 cc of dry air; SYN. r.
See röntgen.

Of or relating to X-rays