Long-term behaviour of 137Cs in spruce bark in coniferous forests in the Czech Republic

Activity concentrations of 137Cs were detected in more than 400 outer spruce bark samples collected at sites variably affected by Chernobyl fallout across the Czech Republic in 1995 and 2010. The temporal changes in the 137Cs activities were found. The mean effective half-life (TEF) for 137Cs in spruce bark was 9.6 years, and the mean environmental half-life (TE) was 14 years. The effective half-lives were significantly higher in areas with higher long-term annual precipitation sums. Coefficient a in linear regression y = ax + b of half-lives on precipitation sums was 0.015 y mm−1 for TEF and 0.036 y mm−1 for TE. The aggregated transfer factor of 137Cs from soil to bark was determined and the pre-Chernobyl bark contamination related to year 2010 was estimated.