The relative efficiency is the ratio of the absolute
efficiency of a detector to the efficiency of a sodium iodide detector.
- Acquire a point source of 60Co of known activity and
place precisely 250 mm from the centre of the top of the endcap of the
detector.
- Collect a spectrum for ~20,000 counts to be accumulated in the 1332
keV peak.
- Determine the net peak area and divide by the live time to give
counts per second.
- Now divide this by the activity of 60Co, allowing for
radioactive decay using the recommended half-life.
- The result is now a measure of the full energy peak efficiency and
can be compared to the efficiency of the NaI detector (1.2 ´
10-3), expressed as a percentage.
- Relative efficiency =
|
Absolute
efficiency |
 |
|
1.2 ´
10-3 |
|
[ AJB to supply image ] |
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