In contamination measurements, what does CPM stand for?

• A. Counts per minute
• B. Coulombs per minute
• C. Counts per second
• D. Curies per meter

Answer: (A)

Counts per minute reflects how many radioactive decay events the detector registers in one minute. It’s a practical, time-based reading used on surveys to indicate contamination levels and to compare readings over time or between locations. The key is that it’s a rate measured by the instrument, not the actual amount of radioactivity itself—the result depends on detector efficiency, the distance from the contamination, and the geometry of the setup. It sits in between a per-second rate (counts per second) and other units that aren’t used for this type of measurement. So, the reading is best described as counts per minute because that’s the standard, straightforward rate the instrument reports.