10. Decision Thresholds and Detection Limits
This chapter shows the statistical error, the decision threshold and the detection limit in
accordance with ISO 11929 for measurements with the LB 134. The uncertainty in the
calibration factor is taken into account in this formula but not in the firmware of the
LB 134.
In the Counter/Timer mode, the calculation formula for activities, contamination and dose
rate in the LB 134 is as follows (the units in all formulas are the same and depend on the
measurement method, e.g. Bq/cm² or µSv/h, etc.):
Basic formula for activity:
Statistical total error including uncertainty in the calibration factor:
Decision threshold:
Detection limit:
Where K calibration factor
Rg gross rate
Ro background rate
tg measuring time in s
to background measuring time in s
A activity
k
1-
= k
1-β
1.65 (quantile)
u(k) / k relative error of calibration factor (= percentage
value divided by 100); if the error in the calibra-
tion factor should not be taken into account,
u(k) will be set to zero in the formulae.
All variables have the same unit. The unit de-
pends on the calibration.
In the Ratemeter mode, the measuring time tg must be replaced by 2 * τ and τ is the entered
time constant in s.
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