GammaVision
®
v7 (A66-BW) 783620H / 1013
6.10. Corrections
If enabled, the following corrections are made on a nuclide-by-nuclide or peak-by-peak basis.
6.10.1. Decay During Acquisition
The decay during acquisition correction is used to correct the activity of nuclides whose half-life is short compared to the spectrum real time.
The correction is:
(82)
where:
DDA
= the decay correction factor
Real time = the spectrum real time (in seconds)
half-life
= the half-life of the nuclide of interest
This can be viewed as scaling up the activity measured to the value of the activity at the start of the measurement. The correction goes to 1 (no change) as acquisition time becomes much smaller than the half-life.
The decay during acquisition technique is superior to making use of a hardware dead-time correction. For example, suppose a sample contains two nuclides, one with a short half-life and one with a long half-life. The count rate of the short half-life nuclide will be higher at the beginning of the count time than at the end of the count. This means more counts per unit time will be accepted at the beginning of the count time than at the end. So even if the count time is extended by the hardware to compensate for the lost counts at the beginning of the counting period, the count rate is so low at the end of the count that not enough counts will be added in. For the long half-life nuclide, the count rate does not change during the count time, so the live-time correction will correctly account for the lost counts during the count time.
6.10.2. Decay Correction
If disabled on the Decay tab or in the
.SDF
file, the decay correction is set to 1.0. If enabled, this correction projects the activity at the time of count back to the time the sample was collected.
This is useful when there is a long time, relative to the half-life, between the sample collection time and the sample count time. The sample collection time is entered on the Decay tab (alterna-
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