Realistic determination of natural radiation exposure in Germany

After their discharge into the environment the mobility of radioactive trace substances is determined by a multitude of physical, chemical and biological processes, each of which has its natural variability. Classical examples of this are the temperature and pH dependence of ion exchange processes or the site, time and species dependent root uptake of trace substances by plants. This means that the exposure resulting from a given discharge of radioactivity depends on the location and time (of year) and that the exposure of a given group of persons will follow a statistical distribution reflecting variabilities in individual behaviour. Due to these variabilities the radiation dose resulting from a given discharge for a given individual can be described in terms of a probability density distribution. These are the scientific facts one is confronted with when making practical radiation protection decisions on the basis of individual dose values. To make informed decisions it is necessary to know the characteristics, ideally nominal values or values derived therefrom, which describe the true statistical distributions in question