Mankind, radiations and radioprotection

After a brief recall of the historic knowledge on natural radioactivity, of the first developments of nuclear medicine and of the emergence of a necessary regulation of the use of these radiations, the author first proposes an overview of the relationship between radioactivity and exposure: sources of natural irradiation, sources of natural origin but modified by technology (medical exposure, professional exposure). Then, the author recalls the origin of radioprotection rules: the International Commission on Radiation Units and Measurements (ICRU), the International Commission on Radiological Protection (ICRP), the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). He addresses the notion of dose with its different types: absorbed dose, equivalent dose, effective dose, specific case of internal exposure with the notion of engaged dose. He gives an overview of the effects of ionizing radiations: deterministic effects, global external irradiation, partial irradiations, and stochastic effects. The next part addresses the radiological protection system: scope of application, the three principles (justification, optimisation, and limitation), and dose limitations. Some matters of debate are reviewed: consequences of accidents of reactors, of Chernobyl and Fukushima (mortality by acute radiation syndrome, thyroid cancers, other cancers, leukaemia, non cancerous diseases, projections and conclusions after the Chernobyl accident), the notions of collective dose and of radio-toxicity, radio-induced cancers and genetic predisposition