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2.10 If cesium is detected in the product under testing, the lower band edge
will move up the line of "zero activity" (i.e. 0 Bq/kg threshold is exceeded).
Moreover, for a more confident conclusion you should wait until the gap between
the edge and the zero line becomes well-defined and lasting enough, and there is no
apparent tendency for a repeated dropping of the lower band edge below the zero
line. One of the examples (Figure 2.19) shows that the lower band edge has crossed
the zero line (red dotted line) and moves upwards after 250 seconds of
measurement, and there are no signs that the direction of the lower band edge will
change "downwards".
Figure 2.19 – Cesium presence monitoring in food with the help of the cursor
2.11 You should keep in mind that the right side of the band gives the most
reliable information about the specific activity, since it uses all data collected at a
given time. Even if the band has not reached its stable condition yet (there is a
tendency to move up or down), the most correct specific activity at a given instant
is depicted in the middle of the right band edge, but not as a mean value throughout
the length of the band. The example illustrates a correct location of the line-cursor
(red dotted line) in the middle of the right edge of the band, which is the most
probable value of specific activity (Figure 2.20 (a)), and an incorrect mid-level
location of the line-cursor on the whole band (Figure 2.20 (b)). A perfect band
shape (as in Figure 2.13), when the middle of the right band edge coincides with
the middle of the whole band length, is rather a rare occurrence.
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