Röntgen
The röntgen (or roentgen, symbol R) was a unit of exposure to X-ray radiation named after the Earth physicist Wilhelm Conrad Röntgen. A dose of five hundred röntgens in five hours was a lethal dose for Humans. A röntgen was also a unit of chroniton radiation, as indicated by The Doctor when Kes was treated in the bio-temporal chamber. ()

Comparative list of units of exposure
 Prior to The Doctor treating Kes with his bio-temporal chamber, he noted that her vitals indicated that her chroniton level was at 79 röntgens. After activating the chamber, and initiating five second pulse anti-chroniton at ten MeVs, her chroniton level dropped to 71 röntgens. With additional bursts, her chroniton level continued to fall from 51 röntgens, to 46 röntgens, to 34 röntgens. After a final twenty MeV burst, her chroniton levels finally dropped to 0 röntgens. ()

 In order to coerce  and Malcolm Reed, who had stowed away aboard a Romulan drone ship, into reinitiating the ship's warp matrix, Admiral Valdore remotely released some of the ship's reactor coolant. Initial readings indicated exposure at 100 röntgens and climbing. ()

External link
 

de:Röntgen
fr:Röntgen
Radiation
Measurements