Doprinos efektivnoj dozi zračenja radonovih i toronovih potomaka

Abstract

Short lived radon and thoron progeny are natural occurring radionuclides which are the most responsible for exposure of people. Main way of irradiating is internal, by inhalation, or ingestion. After inhalation radon and thoron short lived progeny deposit on the inner layers of bronchi and bronchioles and damage surrounding tissue. Activity in the lungs contributes to dose in the lungs, but because of long range of beta gamma and beta radiation, also in the all other human organs. External exposure is from activity in the air surrounding human body. In order to determine airborne activity, model of Brownian motion of radon progeny is developed, using Monte Carlo method. From simulations Jacoby room parameters were determined, which allow to calculate airborne activity in the room. Using this values, deposited activity in the lung can be calculated, which was done in this work. Further absorbed fractions in the sensitive tissue of bronchial and bronchiolar region were calculated using PENELOPE software. Absorbed fraction in sensitive regions is from few to 18% of mean beta spectrum energy. These calculations enabled dose determination in these radiosensitive parts of lugs. DCF for radon progeny was calculated to be 0.21 mSv /WLM , which comprise about 2% of the DCF due to alpha particles from radon progeny. For thoron progeny, DCF is 0.06 mSv /WLM , which comprise 1.5% of the alpha lung dose from thoron progeny. Variation of Jacoby parameters showed that DCF value can be changed in the 35% interval. Absorbed fractions with values up to 18% shows that only that amount of beta and gamma energy is absorbed in the lungs. Because of that it is needed to know doses in all other organs and tissues. In this work doses in all main organs and remainder tissue were calculated for radon and thoron progeny. It is shown that DCF for whole organism is 13.3 and 20.45 mSv /WLM for radon and thoron respectively. At the end contribution from external exposure was determined, for the ORNL phantom in the middle of the standard room, using MCNP software. Radon and its progeny were taken to be uniformly distributed in the room. DCF from radon progeny due to external exposure is 7.37 mSv /WLM . Results in this work presents original scientific contribution of author. The importance of dose calculation is very important in dosimetry. Knowledge of the dose is the first step in determining the radiation effect on humans.