Interest of the mesh dose distributions for the development of an instrumented phantom measuring the effective dose

Workers exposed to radiations at workplaces wear passive or active personal dosimeters which estimate the personal dose equivalent Hp(10). The responses of these monitors depend strongly on the method of detection used and vary with the angular and/or energy distributions of the incident fields. So, the Institute for Radiological Protection and Nuclear Safety (IRSN) is studying the feasibility to develop an instrument which measures directly the quantity evaluating the radiological risk for the workers: the effective dose E. Such an objective implies the determination of the mean absorbed dose in the organs described by the ICRP in its publication 60 and the identification of the nature of the radiation fields. An anthropomorphic phantom equipped with electronic detectors would allow these measurements. The first step of the project is a feasibility study based on numerical models. The Monte Carlo code MCNPX and a mathematical model of an anthropomorphic phantom based on the specifications of Cristy and Eckerman are used to simulate the interactions of the radiation fields with the human body. This paper deals with the validation of the phantom geometry, the method of the dose calculation, as well as the analysis of different numerical tools (mesh or lattice) to determine the most suitable positions of the detectors. First of all, the analysis is carried out for unidirectional extended monoenergetic photon beams. Locations are deduced for several organs, notably liver, lungs, small intestine and brain. Then, as an example, the suitability of the positions determined for the standard configurations (AP, PA and LAT) are studied for a complex photon field case: a photon field produced by the interactions of the neutrons with the glass walls of a glove box. Last, the specificity of the calculations for neutron fields is discussed. (authors)