Voloskyi V. Determination of an effective dose of external radiation in significantly inhomogeneous photon fields

The thesis is devoted to study regularities of doses in organs and effective dose E of the personnel (category A) in case of irradiation in anisotropic photon radiation fields and to development of methods of determining the effective dose of external radiation in workplaces NPP and "Shelter". Means of measuring angular characteristics of the radiation field workers in the significantly heterogeneous (anisotropic) workplace photon fields were proposed. Radiation conditions at the plant and facility "Shelter" were modelled by Monte Carlo methods; 42 phantom measurements in these conditions were conducted and doses to organs along with the effective dose in the high dose rate workplace photon fields were determined. Two effective dose assessment methodologies were elaborated for use depending on the degree of anisotropy of photon fields. For workplaces that are characterized by moderate anisotropy fields assessment of the effective dose E is possible through the use of conversion coefficients for the transition from individual dosimeter readouts to effective dose. For strongly anisotropic fields the method for estimating the effective dose E by simultaneous use of four personal dosimeters located on the torso of a worker around the front and rear was proposed. The results of theoretical calculations were confirmed by phantom measurements in the workplaces at "Shelter" and Ukrainian NPPs. Keywords: effective dose, radiation exposure and its effects, mathematical modelling by Monte Carlo.