Radiation Safety Practice Exam

What is the special unit used to measure absorbed dose?

1. Gray

2. RAD

3. Roentgen

4. Sievert

The correct answer is: RAD

The special unit used to measure absorbed dose is expressed in Grays (and historically in RADs). The Gray is a standard unit in the International System of Units (SI) that quantifies the amount of radiation energy absorbed per kilogram of matter. One Gray corresponds to one joule of energy deposited in one kilogram of material, making it a direct measure of absorbed dose, which is critical in assessing the potential biological effects of radiation on tissue. While RAD is an older unit that was widely used prior to the adoption of the Gray, it is still relevant in the context of absorbed dose measurements as it represents the same concept: the energy deposited in a specific mass of tissue. One RAD is equal to an absorbed dose of 0.01 Gray. The distinction is important historically, but when discussing the current preferred unit for absorbed dose, the Gray is more commonly accepted and is used in modern practice. The other units mentioned, Roentgen and Sievert, measure different quantities. Roentgen is primarily a measure of exposure to ionizing radiation in air, while Sievert is a unit that accounts for biological effect and radiation weight factors, applying to equivalent dose measurements rather than direct absorption. Understanding these distinctions is essential when discussing radiation safety and absorbed doses in