Rad

A rad is a type of measurement. It measures the level of radiation in an area. The Vaults are equipped with radiation sensors that sense the level of radiation. This measurement is reported to the residents on the public announcement system.

In Vault 101 on July 13, 2268, the public announcement system reported the level of radiation -- "Current radiation level - O rads, as always."

Note
In our world, the rad has been replaced by the gray.

Links
((http://www.wikipedia.org/wiki/rad_(unit) : rad)) ((http://www.wikipedia.org/wiki/Gray_(unit) : Gray))