Figure 3 Natural Rock Sample drying loop con
fi
guration
Set the RAD7 pump to ‘ON’ (
Setup,
Pump,
On
[ENTER]
), go to third status window (
Setup,
Enter,
Enter,
Rt. Arrow,
Rt. Arrow.
) and monitor the RH reading. Keep the air circulating
through the loop until the relative humidity (RH) drops to 4% or below.
Th
e drying process may take
many hours.
Once the RH stays at 4% or below, turn o
ff
the pump (
Setup,
Pump,
Off
[ENTER]
), close the ball
valves, disconnect the tubing, and insert the end caps on the Natural Rock Sample tube. Mark the date
on the label and store the Natural Rock Sample with its tubing and Small Drying Tube on a shelf for
between 30 and 50 days before repeating the process.
If the ball valves are opened for any reason on a later date, remove the old label and replace it with a
new label showing the last date on which the valves were closed, and le
ft
closed.
Th
e rock sample will
be ready for another radon check not before one month from that date.
Th
e next measurement should
be made within 50 days of the date on the label, to avoid the risk of moisture creeping in and changing
the emanation e
ffi
ciency, and hence the radon and thoron output, of the Natural Rock Sample.
2.4 Radon Data Assessment
If the Natural Rock Sample was never calibrated, keep the average of the last four readings (3, 4, 5, and
6) in a record for future reference. (Figure 4 on the next page shows a typical data set in DURRIDGE’s
CAPTURE so
ft
ware, with the last four readings selected.) Every standard RAD7 should produce nearly
the same result with that Natural Rock Sample if its sensitivity is as calibrated and if the rock sample is
dry and has been sealed for between 30 and 50 days. For greater reproducibility, 2/3 of the ambient air
radon concentration can be subtracted from the averaged readings to correct for the residual radon in
the air in the system a
ft
er purging. However, if the ambient radon concentration in the air is less than
100 Bq/m
3
(2.7 pCi/L) the error introduced by ignoring it will be less than 1%.
Sec$on 2
RAD7 Radon Sensitivity Check
6
