GammaVision
®
v7 (A66-BW) 783620H / 1013
where:
x
1 x
2 x
3 x
4
= The peak gross counts
= The peak background counts
/ 1
/ 0
Thus, the measurand in Eq. 142 above is the net peak area. According to the ISO NORM documentation, y in Eq. 141 can be the net count (or count rate) or the net activity. Thus, Eq. 142 is compliant with the ISO NORM standard.
Using the familiar terms y
/ N, x
1
/ G, and x
2
/ B, where G is the peak gross counts and B is the peak background, Eq. 142 can be rewritten as:
(143)
In the remainder of this discussion, we will use N as the net peak area y.
6.17.2. The Uncertainty of Net Peak Area
From Eq. 143, it is clear that the variance of the net peak area N is the sum of the variance of the gross counts G and the variance of the background counts B. Therefore, the uncertainty of the net peak area (or the uncertainty of the measurand y) is given by:
(144)
where
σ
B
is the uncertainty in the peak background. The fact that the variance of the gross count
G is G itself has been used in Eq. 144 above. The standard uncertainty propagation rule in ISO
NORM (see Eq. 3 in ISO NORM) is used in deriving Eq. 144 above.
The standard uncertainty u(y) for y in Eq. 141 is related to Eq. 9 in ISO NORM. Because a simplified model is used in GammaVision, the uncertainty calculation has been greatly simplified.
The uncertainty in the peak background
σ
B
is calculated from Eq. 48 on page 250, which we restate here:
(145)
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