Fallout Radionuclides - Application of Geochemical Tracers to Fluvial Sediment - page 53

Table 3.1 General characteristics of 137 Cs

210 Pb ex ,and 7 Be (adapted from Mabit et al. 2008 and

,

Walling et al. 2011 )
Characteristic

137 Ce 210 Pb ex 7 Be

Origin Man-made; nuclear

weapons testing; power
plant releases

Natural geogenic Natural cosmogenic

Half-life 30.2years 22.3years 53.3days

Timeframe of
application

Since 1954; Markers in
1963/1964; 1986

< ∼ 100-
150years

Days < 6months

Temporal fallout pattern Began in 1954; peaked
in 1963/1964 in N. and
S. hemispheres,
respectively; ceased in
late 1970s except for
Chernobyl accidental
release

Continuous with
limited
inter-annual
variations

Continuous; high input
variability with
increases associated
with precipitation events

Estimated process rate
calculations

Annual averaged rates Annual averaged

rates

Events or short-periods
of rainfall; daily to
monthly averages for
some residence time
studies

Global pattern of fallout High in N. hemisphere;
low in S. hemisphere

Unknown Unknown

Depth distribution
• Undisturbed terrain Peak at or immediately

below surface;
exponential decrease
with depth; limited to
about the upper 20 cm

Peak at surface;
exponential
decrease with
depth; limited to
about 30 cm

Peak at surface;
exponential decrease
with depth; limited to
upper 10 cm or less

• Cultivated field Uniform through plough

zone

Uniform through
plough zone

Exponential decrease
from surface;
non-detectable in
recently cultivated land

Scale of area studied Plot to watershed Plot to watershed Plot to short reach scale

Sample collection Simple Simple Requires fine

incremental sampling
that can be difficult

Required analytical
equipment

Normal HPGe ʳ
detector

Broad energy
range Normal
HPGe ʳ detector

Normal HPGe ʳ
detector

Thus, the rate of fallout and its spatial distribution is closely linked to the amount
and intensity of precipitation (Longmore 1982 ; Basher and Matthews 1993 ).
Cesium-137 released during nuclear power plant accidents, such as Chernobyl,
enters the troposphere where its deposition is primarily controlled by atmospheric
circulation and precipitation patterns during and immediately following the event. Its
distribution in soils, then, is much more heterogeneous and local than that associated