The units used to measure contamination are examples of what?

• A. Gray
• B. Becquerels
• C. Disintegrations per minute (dpm) or counts per minute (cpm)
• D. Sievert

Answer: (C)

Contamination readings quantify how much radioactive material is present on a surface by the rate at which decays are detected. That rate is expressed as disintegrations per minute or counts per minute because it reflects how often the detector picks up radiation per minute. These units are tied to the detector’s measurement of events happening per time, not to the energy deposited in tissue or to the total activity of a source. That’s why they’re the best fit for contamination monitoring. For context, gray measures energy deposited per kilogram, Sievert expresses dose taking biological effects into account, and becquerel is total activity (decays per second) of a source rather than the surface contamination rate seen by a detector. In practice, wipe tests or surface surveys are reported in dpm or cpm (and can be converted to Bq if needed, since 1 Bq = 60 dpm).