Relationships between dose rates measured 1 m above ground level and the 137Cs depth distribution in the Chernobyl grounds

The Japan Atomic Energy Research Institute (JAERI), and the Chernobyl Scientific and Technical Center for International Research (CHESCIR), concluded an agreement on the implementation of research at Chernobyl, in 1992. Under this agreement, JAERI was to initiate a study of the characteristics of 137Cs depth distribution in the soil in many points in and around the Chernobyl area. The aim of this research was to understand the relationship between the dose rate above ground level and the 137Cs concentration taking into account the variation of the depth distribution in the ground. The radionuclides released from the Chernobyl nuclear power plant and distributed on the surface of the ground just after the accident, moved into the ground by the mechanism of diffusion and migration with time passing. It is important to know the relationship between the dose rate above ground level and the 137Cs concentration taking into account the variation of the depth distribution in the ground for evaluating the typical activity per unit area or mass of soil nearby by applying in situ measurement. We have obtained a pair of data consisting of the 137Cs concentration and the dose rate at the same point in many different places in and around the Chernobyl area. We tried to relate the activity per unit area to the dose rate above ground level by the Monte Carlo simulation method using the environmental gamma-ray transport calculation code YURI3. The dose rates above ground level were calculated from the 137Cs concentration taking into account the variation of the depth distribution in the ground based on the Monte Carlo simulation method.The result of the comparison of the dose rate calculated with the dose rate measured will be reported in this presentation. (author)