1.4.2 Collecting a Sample
Getting a good sample requires care and practice.
Sampling technique, or lack of it, is generally the
major source of error in measuring the radon content
of water.
Th
e water sampled must be a) representative
of the water being tested, and b) such that it has never
been in contact with air.
To satisfy (a), make sure that the sample has not been
through a charcoal
fi
lter, or been sitting for days in a
hot water tank. To test a well, choose a faucet at the
well, or outside the house, before the water enters any
treatment process. Run the water for an hour, to
make sure that the sample comes freshly from deep in
the well.
To satisfy (b), one of three techniques may be used.
Th
e
fi
rst is to attach a tube to the faucet and
fi
ll the
vial using the tube.
Th
e second is to hold a bowl up to
the faucet so that water over
fl
owing from the bowl
prevents the water leaving the faucet from touching
air.
Th
e vial is then placed at the bottom of the bowl
and allowed to
fi
ll.
Th
e third method combines the
fi
rst two, by having a tube attached to the faucet
feeding water to the interior of the vial at the bottom
of the bowl.
Using the third method, above, allow water to
over
fl
ow freely from the bowl. Take a 250mL vial if
the radon concentration is probably less than 3,000
pCi/L, or 100,000 Bq/m
3
, or a 40mL vial if it is
probably more. Take samples in both sizes if you have
no idea of the concentration. Place the vial in the
bottom of the bowl, and put the tube end into the
vial. Let the water
fl
ow for a while, keeping the vial
full and
fl
ushing with fresh water. Cap the vial while
still under the water. Make sure there are no bubbles
in the vial. Tighten the cap.
Remove the vial from the bowl, dry it and
immediately apply a label stating the date, time and
source of the water.
1.4.3 Setting Up the Equipment
Find the two pieces of Tygon tube (One tube is longer
than the other). In the instrument case, as originally
shipped, the shorter tube is in the 40mL vial
assembled on the aerator in the middle of the case.
With the glass vial removed, the end of the frit should
be 75mm or 3” from the bottom of the aerator cap.
Measure and adjust as necessary.
Th
e longer tube is in
the foam at the near le
ft
-hand corner of the case
(immediately to the right of the 6th 250mL vial).
Th
e
end of the glass frit should be 150mm or 4 7/16” from
the bottom of the aerator cap. Adjust it as necessary.
Pick the tube appropriate to the size of vial
containing the water sample: short for the 40mL vial
and long for the 250mL vial. Push one end onto the
aerator barb, on the side opposite the check valve.
Apply vacuum grease to the two hose barbs on the
top of the aerator cap.
Th
is causes a tight seal to be
formed between the tubing and the hose barbs.
Without su
ffi
cient vacuum grease, air leakage can
occur, resulting in a low radon in water reading.
With the 3” (7.6cm) of 1/4” ID vinyl tubing, connect
the output of the aerator (without a check valve) to a
small drying tube. Use vacuum grease to improve the
fi
t of the tubing over the hose barbs on the aerator
cap. If one end of the drying tube is pink, that end
should face down, towards to the aerator outlet.
Connect the other end of the drying tube, with 1/8”
ID tubing, to an inlet
fi
lter mounted on the RAD7
inlet.
Th
e 1/4” to 1/8” adapter makes this connection
easy and secure. Connect the RAD7 outlet to the
check valve on the aerator.
Th
e Bypass Assembly may
be added as a precaution against foaming, as
discussed in Section 6.5.
With the system as connected so far, set the RAD7 to
purge for another few minutes. While it is purging,
clamp the small drying tube on the retort stand, thus
supporting it vertically.
Stop purging. On the RAD7, go to Setup Protocol
Wat-40, or Wat250, depending on which size of vial is
being used, and push
[ENTER]
. It is essential that the
correct protocol be entered here, because this
controls the pumping and counting cycle, and the
calculation according to the size of sample vial. Set
the Format to short. Place the printer on the RAD7.
Make sure the printer has paper. Switch on the
printer. Switch o
ff
the RAD7, then switch it on again.
It will print its identity and a review of the setup.
While the RAD7 is printing the header, insert the
glass frit into the tygon tubing extending from the
cap. Remove the cap from the water sample and lower
the glass frit into the water. Some water will spill
during this procedure.
Carefully watch the glass frit to
make sure it does not hit the bottom of the vial
; adjust
the position of the tubing if necessary. Screw the
aerator cap onto the vial.
Th
e vial can be inserted in a
slot in the RAD H
2
O case to keep it secure. It must be
upright while aeration is in progress. See Fig. 3 and 4.
Section 1
Getting Started
10
