3. Experimental detail
The 0.7 L RAD7's internal sample cell hemisphere is coated
inside with an electrical conductor. At the center of hemisphere
a solid state, ion-implanted, planner, silicon alpha
detector (semiconductor) is placed which converts a radiation
directly to an electrical signal. The inside of a conductor is
charged relative to the detector to a high potential of
2000e2500 V using a power circuit, thereby creating an electric
field throughout the volume of cell which propels positively
charge particle onto the detector. For determination of radon
concentration RAD7 uses only the polonium-218 and for
thoron uses only polonium-216 signal.
In order to analyze the radon concentration, the stainless
steel probe (Durridge Co., USA) with holes near the tip was
inserted in the soil at a specific depth of 100 cm. Fig. 2 shows
the schematic diagram of soil gas monitoring using RAD7
detector. The probe was then connected to RAD7 detector
through desiccant tube containing CaSO4 and inert filters
having pore size 1 mm for sucking the soil gas from the underground
soil. The depth of the sampling point is determined
by the length of the probe inserted into the ground, taking into
the consideration the location of the sampling points on the
probe shaft. In order to prevent the mixing of soil gas with
fresh air the hole was properly sealed around the probe. The
soil gas is sucked through the tube pipe into the measuring
instrument for 5 min pumping phase and counts for four
5 min cycles for getting the accurate results. During the soil
gas measurement at each site sniff protocol and grab mode
were used.
Fig. 3 shows the schematic diagram of RAD H2O assembly.
A radon tight regent bottle of 250 ml capacity has been used to
collect the water samples. In order to measure the radon