783620H / 1013 6. ANALYSIS METHODS
(198)
where L
pk
is the peak width; and L
Lo
and L
Hi
are respectively the background width below and above the peak as defined for Eq. 145.
Zero Peak Background
If the background is zero, the background variance is taken as the gross counts under the peak.
The peak centroid is at the library peak energy and the peak width is the calibrated peak width.
The background variance is simply given by:
(199)
where G is the peak gross counts.
In other GammaVision reports, the background variance in this case is zero. The MDA calculated then maybe too small if the Currie’s MDA method is used because the MDA counts are only 2.71. MDA calculated from the equation here could be much larger.
This equation is very often used for overlapping peaks where the peak area is attributed to other isotopes.
Peaked Background Correction (PBC)
If PBC is involved, the total background uncertainty is calculated from:
(200)
where PBC is the amount of peak background correction in counts. Note that the PBC correction part is not “scaled” by the ratio of peak width to background width.
6.17.7.2. Negative Peak Area and Confidence Interval
The ISO NORM standard does not make clear how negative peak areas should be handled. However, it can be shown that for the confidence interval, the peak area can be negative.
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