Bentonite suspensions of known concentrations were
used to obtain a proper calibration curve of the count rate
vs. the concentration (Ledin et al., 1993; Missana et al.,
2003). The count rate (expressed as kilocounts per
second, kcps) is, in principle, determined by the number
of particles in the scattered volume. A minimum of 100
particles is required, which corresponds to a count rate
above 10 kcps (Ledin et al., 1993). The bentonite suspension
used in the calibration was a colloidal fraction
with a known concentration separated from the original
Gyeongju bentonite. The average hydraulic diameter of
the colloidal particles in the prepared bentonite suspension
was determined to be about 230 nm. The total
concentration of the bentonite suspension was determined
to be 1942±37 mg/L by a gravitational method.