Which units are used to measure radioactive contamination on surfaces?

• A. disintegration per minute (dpm) or counts per minute (cpm)
• B. rems and sieverts
• C. becquerels and curies
• D. gray and rads

Answer: (A)

Measuring radioactive contamination on surfaces focuses on how many radioactive decays are occurring on that surface per unit time. That rate is what you observe with a detector, giving you disintegrations per minute or counts per minute. These units directly reflect the contamination level on the surface.

Rems and sieverts are dose equivalents, indicating biological risk from radiation, not how contaminated a surface is. Becquerels and curies describe the total activity of a source or material, not the measured contamination rate on a surface. Gray and rad measure absorbed energy as dose, not surface contamination. In practice, contamination surveys report how many decays or detector counts occur per minute (often scaled to a specific area), which is the most direct way to quantify surface contamination.