SARAD RTM1688-2 User Manual page 15

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T(slow) = N / (C * S) = 100 cts / (0.2 kBq/m³ * 8 cts/(min*kBq/m³) = 62.5 min.
Rn
That looks pretty but makes no sense because of the longer response time. So we will set the
interval to 120 Minutes and ask for the statistical error in this case:
N(slow) = C * T * S = 0.2 kBq/m³ * 120 min * 8 cts/(min*Bq/m³) = 192 cts E(1) = 100 % * 1
Rn
* (N) / N = 100 % * 1 * (192) / 192 = 7.22 %
Now one could say
a more trustable result:
E(2) = 100 % * 2 * (N) / N = 100 % * 2 * (192) / 192 = 14.44 %
For interpretation look at begin of this chapter.
Is an observed concentration change statistical significant or not?
If you have a look at the acquired time distribution you will see variations of the
concentration from point to point. The question is now: Is it a real change in the Radon
concentration or only a statistical fluctuation?
The test is very simple: Define a confidence level with respect to your needs and look at the
statistical error bands of the two points of interest. If the error bands do not overlap each
other, the change in the Radon concentration is significant otherwise it "can be or not can
be".
Example 1:
Reading 1: 1500 Bq/m³ ±10%  error band [1350 ... 1650 Bq/m³]
Reading 2: 1300 Bq/m³ ±13%  error band [1131 ... 1469 Bq/m³]
The upper limit of the error band of the reading 2 is higher than the lower limit of the error
band of reading 1. Because the "true" value could be placed within 1350 Bq/m³ and 1469
Bq/m³, the variation of both readings is not statistical significant.
Example 2:
Reading 1: 1500 Bq/m³ 10% error band [1350 ... 1650 Bq/m³]
Reading 2: 1000 Bq/m³ 15% error band [850 ... 1150 Bq/m³]
The error bands of the readings do not overlap each other. Therefore, a statistical significant
concentration change is given.
Two arbitrary points of a measurement series may be considered using this test. It is not
necessary that the points are direct neighbours.
User Manual RTM1688-2 06-02-2019.docx