Unit of measurement commonly used on high range RADIAC scales?

• A. Rem (REM)
• B. Sievert (Sv)
• C. Curie (Ci)
• D. Roentgen (R)

Answer: (D)

When you read high-range RADIAC scales, you’re looking at exposure rate in air—the amount of ionization the radiation creates in a given mass of air. The unit that has long been used for this purpose is the Roentgen. It directly measures exposure, which is why radiac meters with wide ranges typically display in R (or R/h for rate). The other units measure different things: rem and sievert relate to dose equivalent (biological effect) and curie relates to the activity of a radioactive source. Those aren’t the quantities a high-range radiac is designed to read, so roentgen is the most appropriate and practical unit for these instruments. Note that in modern SI usage, exposure is expressed in coulombs per kilogram, but historically and in many field radios, Roentgen remains the standard.