783620H / 1013 6. ANALYSIS METHODS
(which are printed on the nuclide/peak matrix) you can determine how relevant the selected
MDA value is to the physical situation. The MDA reported for the nuclide is the value for the first peak in the library.
6.9.1. Computing MDA Values
MDA values for many methods depend on area and background values. Area and background determination varies from method to method. The information needed to validate the MDA results can be found in the peak analysis Details dialog (Fig. 248; refer also to Section 5.5.6.3); the analysis options (
.SDF
file) for the spectrum (Section 5.5.1.1); reports (Chapter 7); and manual integration of the spectrum peaks.
Fig. 248. Peak Analysis Details Dialog is One Source of Data for the MDA
Calculation.
6.9.1.1. Area Methods
A
1
Gross area under the peak determined by integrating the peak with a width of 2.5 times
FWHM (counts). Areas computed in this manner are used in Methods 4, 11, and 14 below.
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®
v7 (A66-BW) 783620H / 1013
To determine the area:
1) Determine the (decimal representation) centroid energy of the peak.
2) Determine the (decimal representation) channel of this centroid (based on the energy calibration).
3) Determine the (decimal representation) FWHM of this peak (based on the FWHM calibration at the centroid channel).
4) Determine half of the FWHM range (denoted as I
L
), which is calculated as the integer representation of (1.25 * FWHM + 0.5). Note that this value is capped at 100.
5) Determine the centroid for integration (denoted as C
I
), which is simply the centroid channel determined in step (2) rounded to the closest whole (integer) number.
6) Determine a lower channel of integration (denoted as C
Low
) as follows. This value has a minimum value of 1.
C
Low
= C
I
- I
L
7) Determine an upper channel of integration (denoted as C
High
) as follows:
C
High
= C
I
+ I
L
8) A
1
is then simply the sum of all channels from C
Low
to C
High
.
A
2
Net peak area reported on the Identified Peak Summary Report or peak Details dialog
(counts). Areas computed in this manner are used in Methods 9 and 10 below.
A
3
Gross area under the peak determined by integrating the peak with a width of 2.5 times
FWHM minus one channel on the high- and low-energy side of the peaks. Areas computed in this manner are used in Method 13 below.
To determine the gross area:
1) Determine the (decimal representation) centroid energy of the peak.
2) Determine the (decimal representation) channel of this centroid (based on the energy calibration).
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