SARAD Thoron-Scout User Manual page 11

SARAD
GmbH
intervals have to be averaged to get a usable result. This procedure is nothing else than to
create an integration interval long enough to meet the Detection limit for the applied Radon
concentration. To avoid zero readings, set the integration interval with respect to the lowest
expected concentration level during measurement.
The mean („true") value of the number of decays during an integration interval in case of a
Radon concentration in the surrounding of the detection limit is less than 16 and therefore
the statistical fluctuations have to be derived by the Poisson distribution. The stated
confidence interval gives the probability that the detected number of decays within the
interval is not zero.
Example:
Determination of the detection limit of the Monitor using the „Fast-Mode" and an integration
interval of 60 Minutes. The confidence interval shall be 95% (that means in about 95 from
100 intervals a no zero reading should appear):
Required mean value (number of counts from the table): N = 3.
Calculating the detection limit by the formula:
C = N / (T * S) = 3 cts / (60 min * 8 cts/(min*kBq/m³)) = 0.00625 kBq/m³ = 6.25 Bq/m³
The detection limit in this case is 6.25 Bq/m³.
Manual_ThoronScout_EN_02-07-15.doc
Thoron-Scout
Confidence Interval
63,2 %
95 %
99.75 %
Required Mean Value for
N at the Detection Limit
1
3
6
11