3.2 Data Conversion Formulas
3.2.1 Fritz Weigel Formula
Th
e RAD7 gives an accurate reading of the radon
concentration in the closed air loop. With the Water
Probe, this air reaches equilibrium with the
surrounding water. To convert the air concentration
to water concentration, the air concentration must be
multiplied by the partition coe
ffi
cient, which is given
by the Fritz Weigel equation (Weigel, 1978):
a = 0.105 + 0.405 * exp(-0.0502*T)
where T is the temperature in degrees Celsius.
At 10 degrees Celsius, a is around 0.35, giving, at
equilibrium, a three-to-one ratio of radon in air to
water.
Th
e Fritz Weigel formula is applied
automatically in CAPTURE when the Water Type is
set to Fresh Water in the Run Parameters Window, as
shown in Fig. 3, below.
3.2.2 Schubert Et. Al. Formula
If the Water Type is set to Saline Water in
CAPTURE’s Run Parameters Window, the radon in
water concentration is calculated using the Schubert
et al. formula, which is a function of both water
temperature and salinity. (See Schubert et. al., 2012.)
Th
e Run Parameters Window provides a
fi
eld for
specifying the salinity of the water, in parts per
thousand. Note that this formula is suitable for water
samples with any degree of salinity, including zero.
When the salinity value is set to zero, it produces
results that are nearly identical to those produced by
the Fritz Weigel formula.
Fig. 3 The CAPTURE Run Parameters Window
Section 3
Data
10
