DURRIDGE NATURAL ROCK SAMPLE User Manual - Page 8
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2.5 Multiple RAD7s
Before using the Natural Rock Sample to check a RAD7's radon sensitivity, the Natural Rock Sample
must be left sealed for a month, in order for the radon inside the container to reach equilibrium. That
means a RAD7 can have its sensitivity checked each month on a regular basis. However, there is
nothing to stop us hooking up multiple RAD7s in series in the loop connected to the Natural Rock
Sample. This increases the volume of the loop and hence decreases the radon concentration in the loop,
but by a predictable and reproducible amount. This method is recommended for checking up to six
RAD7s on a monthly basis.
For the sake of argument, using rounded figures, let us assume that the total activity of radon inside the
Natural Rock Sample container, when in equilibrium, is equal to 2 Bq. Let us also assume that the
Natural Rock Sample and tubing has an air volume of 500ml while a RAD7 is 1L. Then when the RAD7
is connected up to the Natural Rock Sample and the radon distributed around the loop, the radon
concentration will be 2 / 1.5 = 1.333 Bq/L = 1333 Bq/m
3
. If every additional RAD7 adds 1L to the loop,
then four RAD7s would total 4.5L, including the Natural Rock Sample and tubing. The radon
concentration in the loop would then become 2 / 4.5 = 0.444 Bq/L = 444 Bq/m
3
. While this is less than
1333 Bq/m
, it is still enough to make a good reading in two hours and a high precision reading in 12
3
hours.
Figure 5 Multiple RAD7 Sensitivity Check Configuration
Each month, all four RAD7s can be connected in series with one another and thoroughly purged and
dried out, before being connected to the rock sample to obtain a sensitivity check. Each month the
setup should be identical, with the same number of RAD7s and the same pieces of tubing to connect up
the entire loop. During the measurement all the RAD7 pumps, except one, should be set to OFF
Setup, Pump, Off, [ENTER]
(
.)
If any of the RAD7s had developed a leak, the radon concentration in the loop would fall rapidly. Thus
in addition to keeping a record of the average readings during the check, for each month, a record of
Sec$on 2
RAD7 Radon Sensitivity Check
8