| quotient of dQ by dm, where dQ is the absolute value of the total charge of the ions of one sign produced in air when all the electrons and positrons liberated or created by photons in air of mass dm are completely stopped |
X = dQ/dm
Note 1 to entry: This quantity is expressed in coulombs per kilogram (C/kg). Formerly it was expressed in roentgens R (1 R = 2,58 x 10−4 C·kg −1).
Note 2 to entry: This term is used in the metrology of ionizing radiation.
Note 3 to entry: This entry was numbered 393-14-57 in IEC 60050-393:2003.