DANB Radiation Health and Safety (RHS) Practice Exam

Which unit measures the effect of Xrays on tissues?

1. Rad

2. Rem

3. Roentgen

4. Angstrom

The correct answer is: Rem

The rem, which stands for roentgen equivalent man, is the unit used to measure the biological effect of ionizing radiation, including X-rays, on human tissues. This unit takes into account both the amount of radiation absorbed by the tissue (measured in rad) and the biological impact of that radiation, providing a more comprehensive measure of the adverse health effects caused by exposure. This distinction is important because not all forms of radiation have the same effect on tissue; therefore, the rem adjusts for the type of radiation, making it a crucial unit for assessing potential risk to health from exposure to X-rays. In contrast, the rad measures the amount of radiation energy absorbed by a material but does not factor in the biological effects specific to human tissues, which is why the rem is considered a superior measure for evaluating the impact of X-ray exposure on health. The roentgen measures the quantity of X-rays or gamma rays in air and is not a direct measure of tissue impact. Meanwhile, angstrom is a unit of length commonly used in atomic and molecular scales, not related to radiation measurement at all.