If the Natural Rock Sample has been calibrated by DURRIDGE Company, the calibration certi
fi
cate
gives the standardized average of readings 3, 4, 5 and 6, obtained with the standard setup, a well purged
and dry RAD7 and 30-minute cycles.
Th
us the ratio of the value stated on the rock sample calibration
certi
fi
cate to the measured standardized average gives you the correction factor directly. RAD7
readings multiplied by that ratio will give readings consistent with the DURRIDGE calibration system
to within 15%.
You may also, if you wish, calculate the total radon amount in the air loop, and hence originally in the
Natural Rock Sample container. If the radon amount is Rn and the volume of the air loop is V, then the
radon concentration is Rn/V.
Th
e air volume in the Natural Rock Sample is about 460ml, a standard
RAD7 is 800ml, and the tubing with small drying tube is 16ml, for a total volume of a standard Natural
Rock Sample system with standard RAD7 of 1.275 L. If Rn is expressed in pCi, then the radon
concentration will be Rn/1.275 pCi/L. If Rn is expressed in Bq, then the radon concentration will be
Rn/1.275 Bq/L, or 1000 * Rn / 1.275 Bq/m
3
.
In pCi, Rn = 1.275 * radon concentration in pCi/L.
In Bq, Rn = 0.001275 * radon concentration in Bq/m
3
If the certi
fi
ed and observed standardized average values di
ff
er by more than 15%, we recommend that
the RAD7 be returned to DURRIDGE Company for service. If, a
ft
er several monthly sensitivity checks,
there is a consistent ratio between the observed and the certi
fi
ed standardized average radon
concentration, you may consider applying a multiplier to all readings made with that RAD7, to bring
them in line with the Natural Rock Sample standard. If you notice a big jump, up or down, in the
reading, from the previous month,
fi
rst look to see if the RAD7 was properly purged before the
measurement was started. If there is no obvious reason for the jump, the RAD7 should be returned to
DURRIDGE for service.
Figure 4 Graph of Natural Rock Sample sensitivity test data
Sec$on 2
RAD7 Radon Sensitivity Check
7
