INTRODUCTION
Th
e Water Probe is an accessory for the DURRIDGE RAD7 Electronic Radon Detector. It is a device to bring the
radon concentration in a closed air loop into equilibrium with the radon concentration in the body of water in
which it is submerged. It consists of a length of hydrophobic yet gas-permeable membrane tubing, called an
“exchanger”, that brings the radon in a closed air loop into equilibrium with the surrounding water.
Th
e radon in
the air loop is monitored continuously by the RAD7.
Th
e partition coe
ffi
cient, the ratio of radon concentration in the water to that in the air at equilibrium, is
determined by the temperature at the air/water interface.
Th
is temperature is measured with a temperature probe
inserted into the water. As an example, at a water temperature of 10 degrees Celsius, the partition coe
ffi
cient is
about 1:3.
Th
at means there is three times higher concentration of radon in the air than in the water, so there is,
in e
ff
ect, a gain of three times in the sensitivity of the system to radon in water, compared to radon in air.
It takes time for the water to deliver radon to the air loop and for the RAD7 to respond to the changed radon
concentration. With optimum con
fi
guration the response time of the system is around 2 hours.
Fig. 1 Assembled Water Probe
Introduction
4
CAUTION
There is a potential for biofouling to occur in long-term monitoring applications. The
Water Probe should therefore be inspected periodically to ensure that there is good
contact between the radon exchange tubing and the surrounding water.
