What is the unit of measurement for radiation dose?

• A. Roentgen
• B. Rem or millirem
• C. Sievert
• D. Becquerel

Answer: (B)

The main idea here is dose equivalent—the quantity that represents the potential biological effect of ionizing radiation on a person. Dose is different from exposure (which is about ionization in air) and from activity (which is how many decays a source is emitting). The dose equivalent factors in both the type of radiation and the sensitivity of body tissues, giving a number that better reflects potential harm.

Rem (roentgen equivalent man) and its subunit millirem are units that express this dose equivalent. They have been used historically to quantify how much radiation a person receives in terms of potential biological impact. That’s why, in many safety and training contexts, rem or millirem are the go-to units for dose.

In modern SI units, the dose equivalent is expressed in sieverts, with 1 rem equal to 0.01 sievert. So the choice reflects traditional practice, and rem/millirem remains a common way to talk about dose, even though sieverts are the official SI standard.