• A survey in Kawauchi Village, Fukushima Prefecture, shows that the depth distribution of radioactive cesium slightly widened in the depth direction over time.
• Distribution tends to be deeper in slopes than in flat ground such as ridges and paths through forests.

Fig.1　Depth distribution of ¹³⁷Cs concentrations in forest soil
(Data on the mineral layer [A to B layers] except for the surface organic layer)
Sampled at two different times (Sampling time: January 2013 and October 2014)

Fig.2　Sampling locations

Fig.3　Elapsed years since the accident and the ratio to total amount of below-ground ¹³⁷Cs (%)
(Sample data for Yamakiya, Kawamata Town)

• The amount of ¹³⁷Cs deposited in the litter layer has been decreasing over time.
• The amount of ¹³⁷Cs deposited in a 0-3 cm layer of surface soil has been decreasing almost steadily or gradually since 2014.
  → This shows that cesium has hardly migrated from the surface layer to deeper layers, suggesting the possibility that 137Cs remains in the litter layer and the surface soil within a depth of 3 cm.

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