The sievert: an enigmatic unit.

The concept of effective dose with its unit, the sievert, is frequently misunderstood. Originally conceived to simplify radiation protection management, this concept is also proposed for another and very ambitions objective: a quantitative evaluation of the risks of radio-induced diseases, whatever the dose, the dose rate, the nature of radiation.... However, using the sievert for the prediction of risks of cancer or hereditary diseases is hazardous, and errors of prediction have been observed these last decades, for example the lack of prediction of the number of thyroid cancer in the very young children after the Chernobyl accident, and the overestimation of the risks such as leukaemia, other cancer and hereditary diseases. What are one sievert and its subunits?