National Physical Laboratory

Identification of significant emissions

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A single emission per nuclear disintegration is referred to as an emission probability of 100%.

60Co is an example of a radionuclide that produces more than one emission per disintegration; these are effectively emitted simultaneously. 55Fe produces less than one emission per nuclear disintegration.

Many radionuclides decay via several different decay paths and for each path, several emissions may occur in very short succession. Regardless of how many of these emissions interact with the detector (one, several or all), only one event is registered by the instrument;

This effect is known as 'coincidence summing' (Please refer to the example of decay scheme correction : 111In on page 5).

In practice, using an instrument which would only respond to one type of emission may simplify the calculation of surface activity. For example, in the case of 60Co, it is normal practice to monitor with a beta detector that has minimal gamma response. 

Once the energies of the detectable emissions are known, the 2π efficiency for an ideal source of that radiation type and energy can be determined by interpolation of the energy response curves.

 

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