How are fixed and loose surface contaminations measured?

• A. Measured in CPM (counts per minute).
• B. Measured in mSv.
• C. Measured in Ci.
• D. Measured in rem/h.

Answer: (A)

Surface contamination is assessed by detecting radioactive decays that occur on a surface using a contamination monitor and recording how many events are detected per minute. That rate, shown as counts per minute, directly reflects how much radioactive material is present on the surface and how likely it is to transfer. It’s a practical, surface-based measurement for contamination control actions, such as decontamination steps.

Dose units like mSv measure the biological effect of radiation, not how much material sits on a surface. Total activity units like Ci describe how much radioactive material exists in a sample, not how it’s distributed on a surface. Dose-rate units like rem/h indicate how quickly dose would accumulate at a location, not the contamination level on a surface. Hence, CPM is the appropriate way to express fixed and loose surface contamination.