Geoscience Reference
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Fig. 3.3
Variations in fallout radionuclides with depth in soils from Morocco.
a
137
Cs in an undis-
turbed soil;
b
137
Cs in a ploughed agricultural soil;
c
210
Pb
ex
in an undisturbed soil;
d
210
Pb
ex
in
a ploughed agricultural soil;
e
7
Be in an undisturbed soil;
f
7
Be in a ploughed agricultural soil
(adapted from Mabit et al.
2008
)
returned to the Earth's surface within a few days (Fig.
3.4
). This atmospherically
deposited
210
Pb is referred to as unsupported or excess
210
Pb
ex
to distinguish it
from the
210
Pb created by, and in equilibrium with,
226
Ra in soil. The amount of
supported
210
Pb in the soil can be determined on the basis of the
226
Ra activity and,
thus, removed from the total to determine the unsupported
210
Pb
ex
in the soil derived
from atmospheric deposition.
Like
137
Cs, an undisturbed soil profile that has been subjected to no erosion or
deposition is thought to reflect the atmospheric
210
Pb
ex
flux to the Earth's surface.
Unlike
137
Cs, however, the
210
Pb
ex
is essentially constant through time (although
minor variations in the flux of
210
Pb
ex
to the Earth's surface have been noted; Preiss
et al.
1996
). Thus, while the inventory of
137
Cs in an undisturbed soil that has been
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