2018 Volume 52 Issue 2 Pages 155-162
Rainwater has been sampled on a monthly basis at the University of Tsukuba, Japan, since 2009. The serious accident at the Fukushima Daiichi Nuclear Power Plant in March 2011 resulted in the atmospheric emission of large quantities of radionuclides. Monthly 129I deposition was monitored for 19 months before and 41 months after the accident to estimate its influence at Tsukuba. Before the accident, 129I concentration in rainwater was in the range (0.19–2.6) × 108 atoms L–1. There was a rapid increase after the accident, with the highest 129I concentration recorded in March 2011 as (5.4 ± 0.8) × 1010 atoms L–1. It took approximately 1 y for the 129I concentration to return to pre-accident background levels, due to continuing resuspension and deposition. Measured decreases in 129I concentration in rainfall showed good agreement with double-exponential modeling.