Gray (unit) Gray (unit) The gray (symbol: Gy) is a derived unit of ionizing radiation dose in the International System of Units (SI). It is defined as the absorption of one joule of radiation energy per kilogram of matter. It is used as a unit of the radiation quantity absorbed dose which measures the energy deposited in a unit mass at a certain position, and of the radiation quantity kerma, which is the amount of energy that is transferred from photons to electrons per unit mass at a certain position. The corresponding cgs unit to the gray is the rad (equivalent to
UNIT to be some kind of covert counter-terrorist unit. Although the Brigadier originally states that UNIT do not arrest people, as of the 21st century, UNIT has the authority to detain persons indefinitely without trial, appeal, outside contact or legal representation, as experienced by Toshiko Sato before she was recruited to work for the British government by the Torchwood Institute in a flashback in the "Torchwood" episode "Fragments" (2008). The organisation was rearranged by Kate Stewart, the daughter of Brigadier Lethbridge-Stewart. In "The Power of Three" (2012), Kate heads UNIT's scientific research department, which now has authority over the military branch.