Atomic Structure
Activity and Count Rate
To distinguish activity from count rate and explain why background radiation must be considered when taking measurements.
What you will learn
The difference between activity and count rate
Why activity is measured in becquerels
How a detector measures radiation counts
How to subtract background radiation from readings
Why measured count rate is not the same as source activity
Explanation
Activity counts all decays in a source per second, while count rate measures detections per second. A detector misses some radiation because of geometry, absorption and its efficiency. Subtract background to estimate source count rate and use longer intervals or repeats to reduce relative random variation. Example: A detector records 300 counts in 60 s. Calculate count rate. 5 counts/s. Rearrange the relationship before substituting if a different quantity is required. Identify cause and effect.