True Coincidence Summing Correction in Gamma Spectroscopy

For environmental measurement that involve a limited set of radionuclides, it would
be better to make the measurements relative to a reference standard for each nuclide
rather than depending on upon interpolation of a calibration curve. This interpolation
introduces extra uncertainties added to those involved in producing a point on the
curve. Due to the above mentioned factors, the calibration curve may not be
accurate. If the spectrum analysis program requires a calibration curve, then a curve
must be created. However, the following correction factors should be considered in
using calibration curves;
Figure-1.9 Full peak energy calibration curve for a Marinelli Beaker
i. Dead-time correction
The dead-time correction factor is (1-Rτ) -1 , where τ is the dead-time value
selected for the dead-time module and R is the total count rate above the
threshold including the digital overflows. Such factor depends on the sample’s
count rate.
ii.
Pile-up correction
A pulse will be counted and stored whenever it is not followed or preceded by
another pulse during a certain period of time τ, the resolution time of the electronic
system. Using the Poisson distribution, the probability of a random coincidence,
p c , within τ is;
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