134Cs and 137Cs radioactivity in soil and moss samples of Jeju Island after Fukushima nuclear reactor accident

• 134Cs and 137Cs distributions were investigated in soil and mosses of Jeju Island.
• Large areal variation exists in the soil but the variation is small in the mosses.
• The ratio 134Cs/137Cs in the soil is much smaller than the reference value of 1.0.
• 134Cs/137Cs in the mosses is close to the reference value.
• The activity of 137Cs in soil originating from the Fukushima accident was estimated.

Specific activities of 134Cs and 137Cs in surface soil and moss samples were investigated at 12 locations of Jeju Island, Korea. Specific activities of 134Cs and 137Cs in the surface soil vary from less than MDA to 17 Bq/kg and from 12 Bq/kg to 109 Bq/kg, respectively. Specific activities of 134Cs and 137Cs in moss samples lie in the range 6 Bq/kg–39 Bq/kg and 15 Bq/kg–41 Bq/kg, respectively. The activity ratios 134Cs/137Cs in the soil samples are much less than the reference value of about 1.0, but they are close to 1.0 in the moss samples. Average amount of 137Cs added to the surface soil after the Fukushima accident is estimated to be 7.8±1.7 Bq/kg. The depth profile of 137Cs specific activity has a lognormal shape with a peak between 5 cm and 7.5 cm below the ground. For the cored soil sample, 134Cs was detected up to 3 cm below the ground.