783620H / 1013 6. ANALYSIS METHODS
(60)
where:
A
Ei
Br i
= the activity of nuclide peak i at energy E per Eq. 59
= the gamma/disintegration of the i th
peak
n
= the number of peaks included in the activity
6.7.2. Nuclide Counting Uncertainty Estimate
Many radioisotopes have more than one peak useful for calculating the measured activity of the isotope. The uncertainty caused by counting statistics can vary widely among those peaks. This variation can be caused by differences in the net counting rates in the peaks or the background levels under the peaks. GammaVision utilizes a relatively simple yet statistically rigorous method for choosing the peaks to achieve optimum precision. When more than one peak is available, the software performs two assessments:
1) It finds the peak with the smallest percent standard deviation.
2) It computes the percent standard deviation for the linear average of all peaks detected according to the criteria in Section 6.7.
The option which yields the lowest percent standard deviation is the method used to calculate the nuclide counting uncertainty for the radioisotope. The mathematical process for this selection is summarized below:
Assume
σ
A
is the reported nuclide counting uncertainty,
σ
Pi
is the counting uncertainty for the i
th
peak and n is the total number of peaks used to calculate the nuclide activity. All the uncertainties are relative.
Furthermore, let us define
σ
Pmin
as the minimum counting uncertainty of all the n peaks:
(61)
where MIN is the minimum function which returns the minimum value from a list of values in the parenthesis (from 1 to n above).
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