What Units Are Used To Measure Absorbed Dose?
Absorbed dose is measured in grays (abbreviation Gy). One gray corresponds to one joule of radiation energy deposited in one kilogram of matter. (Note: It would require 320,000 joules of energy to boil one kilogram [one litre] of water). A uniform dose of 3 to 5 Gy to the whole body will kill fifty percent of people exposed in one to two months. This is a large unit and the milligray (mGy), which is one thousandth of a gray, is more commonly used. When radiation interacts with living tissue the effect it has varies with the type of radiation. Alpha rays are 20 times more effective than beta, gamma or X-rays at causing tissue damage. To allow for this, the dose in grays is multiplied by an effectiveness factor and the new units are called sieverts (abbreviation Sv) and the dose is called the equivalent dose. A one milligray dose of alpha rays is equal to 20 mSv (millisieverts) of equivalent dose. A one milligray dose of beta rays is equal to 1 mSv equivalent dose because the effectivene
