Rad
d
The rad was a unit of radiation dose. This form of measurement was still used by the Federation during the 24th century.

Comparative list of radiation doses
1 millirad = 1/1,000 rad
 In 2369, Dr. Julian Bashir bombarded a sample of the aphasia virus, grown on tetracitrus gel, with hyperonic radiation at 430 millirads. ()

 In 2151, Captain Jonathan Archer asked his science officer Sub-commander T'Pol on how bad the radiation was on Terra Nova, a planet  was orbiting. T'Pol replied that it was less than 800 millirads and that a few hours of exposure to it wouldn't pose a risk to a landing party. ()

1000 millirads = 1 rad
 In 2371, Miles O'Brien began repeatedly time shifting a few hours into the future due to the combination of cloaked Romulan warbirds and an accident on the station in which he was infected with delta-series radioisotopes. During one of O'Brien's time shifts, he witnessed the destruction of Deep Space 9. To control his time shifting and to discover how DS9 was destroyed, he had Dr. Bashir outfit him with a device to inject him with a 2 rad dose of delta-series radioisotopes, which eventually led to his death. He was later "replaced" by a future Miles O'Brien. ()

 In 2368, Dr. Beverly Crusher told Geordi La Forge that the quaratum in one of the 's cargo bays had radiation levels of 83 rads, rising at four rads per minute. La Forge commented that quaratum got unstable at 350 rads. ()

 The external temperature of a Federation shuttlecraft, utilizing metaphasic shielding, could tolerate radiation levels that approach 10,000 rads and temperatures of 1.9 million K, while maintaining an internal cabin temperature of 21 °C. ()

 In 2370, while trying to evade a rogue Borg ship, Beverly Crusher, in command of the Enterprise-D, took the ship into the corona of a star using metaphasic shielding. The Enterprise however couldn't stay in the star for long and Ensign Taitt informed Crusher that the radiation from the star was at 10,000 rads and rising. The Enterprise was later able to destroy the approaching Borg ship with the help of a solar flare. ()

External link
 

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Measurements
Radiation