The relationship between fem and 226Ra activity concentrations,
determined previously in soil samples from the
same lithological units [40], is shown in Fig. 4. Values of
fem about 0.04 (in a red circle) seem to be typical for our
samples. The samples with values higher than 0.1 might
have been affected by groundwater, resulting in radium
distribution predominantly on the grain surface [19–21].
All soil samples on carbonate rocks with increased 226Ra
values (above 100 Bq kg-1), are also characterised by
increased fem, which is in favour with the assumption of
radium concentrated on the surface of soil grains. In the
previous study of radionuclides in soil [40] it was concluded,
that high 226Ra concentrations on carbonate rocks
can be explained by migration of 238U and 226Ra by water
from nearby rocks with slightly elevated 238U contents,
followed by subsequent wash out of more mobile 238U.
Beside samples on carbonate rocks (C), also soil samples
on clastic sediments containing clay (B1) show wide
scattering of fem values. These samples show elevated fem,
but usually moderate radium concentrations. Increase of
fem could thus again be assigned to distribution of 226Ra
atoms on grain surface.
The relationship between fem and 226Ra activity concentrations,determined previously in soil samples from thesame lithological units [40], is shown in Fig. 4. Values offem about 0.04 (in a red circle) seem to be typical for oursamples. The samples with values higher than 0.1 mighthave been affected by groundwater, resulting in radiumdistribution predominantly on the grain surface [19–21].All soil samples on carbonate rocks with increased 226Ravalues (above 100 Bq kg-1), are also characterised byincreased fem, which is in favour with the assumption ofradium concentrated on the surface of soil grains. In theprevious study of radionuclides in soil [40] it was concluded,that high 226Ra concentrations on carbonate rockscan be explained by migration of 238U and 226Ra by waterfrom nearby rocks with slightly elevated 238U contents,followed by subsequent wash out of more mobile 238U.Beside samples on carbonate rocks (C), also soil sampleson clastic sediments containing clay (B1) show widescattering of fem values. These samples show elevated fem,but usually moderate radium concentrations. Increase offem could thus again be assigned to distribution of 226Raatoms on grain surface.
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