The Radial Distribution of Cesium-137 in Trees

Frans Johansson

Cesium-137 can be introduced into the environment through two processes, nuclear bomb explosions and leakage from nuclear power plants. Due to the nuclear meltdown at Chernobyl, the 26th of April 1986, a significant pulse of cesium-137 was injected into the environment. Trees are one type of reservoirs cesium will be sequestered into, partly via leaf uptake, but mainly via root uptake. By measuring the cesium concentration in consecutive tree rings within the wood of a Swedish pine tree, I established its radial distribution. The pattern showed a large peak of cesium about 8-13 mm in from the surface of the tree. With the help of a diffusion model I determined the diffusion coefficient for cesium in wood, 1.3*10-9 cm²/s. Aggregate levels of ¹³⁷Cs in wood was also calculated and used in a preliminary risk-assessment. It was found that if wood-ash is used as a part of fertilizer for crop plants there is a potential and unacceptable risk to human health.