STUDY OF THE INFLUENCE OF SOIL MOISTURE AND GRAIN SIZE ON RADON EMANATION FROM SOIL USING AN ADVANCED MULTIGRAIN MODEL.

Among the most important factors that influence radon emanation from soil particles is the soil moisture and grain size. Both components, in its own way, modify the length of a trajectory that radon atom pass through in a volume of the soil pores. To better understand their impact on an emanation, we have developed our own computer program that can simulate the 222Rn emanation process in the soil environment, using an idea of a multigrain model. In our case, the central, radium-bearing soil grain is surrounded by 1330 adjacent grains of the same size forming a cubic structure and the moisture in a space of the soil pores is differently distributed. The simulation process is based on a two different distribution of 226Ra in soil grains (homogenous and heterogenous), while several variants of the thickness of an escape layer are analyzed for grains of different sizes and moisture contents.

INFLUENCE OF AIRWAY GEOMETRY ON RADON RISK ASSESSMENT IN ADULTS AND CHILDREN (MICRODOSIMETRIC APPROACH).

The aim of this work was to use the microdosimetric threshold energy model to study the effects of alpha-emitting 222Rn progeny on the probability of developing lung cancer. The results suggest that the radiation risk may increase by several times as the thickness of the surface layer decreases. The thicker the protective mucus layer and the deeper the sensitive target cells are located in the tissue, the less radiation damage the same dose produces. These findings have been applied to children of various ages. As children grow older, their lungs enlarge, the mucus layer thickens and the cells sensitive to radiation damage move deeper into the lung tissue, resulting in a reduction of radiation risk. The fraction of affected target cells is not only a function of dose but also of lung tissue depth. The results indicate that children can be several times more vulnerable to radiation than adults.

Radon as a Tracer of Lung Changes Induced by Smoking.

After smoking, exposure to radon and its progeny is the second leading cause of lung cancer. The probability of inducing lung carcinomas by inhaled radon progeny depends on the deposited radiation dose, and is significantly affected by physiological and morphometric changes induced by smoking. Due to irritation of the airways, the inhalation of cigarette smoke leads to the hyperproduction of mucus. Two concurrent processes occur: on one hand, increased production of mucus protects the target cells against radiation damage; on the other hand, in the case of long-term smokers, a chronic lung obstruction develops, causing an increase in the radiation dose to the lungs. Depending on the duration and intensity of smoking, these processes contribute to the final radiation dose with different weights. The primary objective of this study was to investigate to what extent these smoke-induced changes can modify the resulting absorbed dose of inhaled radon progeny relative to healthy nonsmokers. Since the bronchial dose depends on the degree of lung tissue damage, we have used this dose as a tool for detecting the effects of smoking on the lung epithelium. In other words, the biological effect of radon served as a tracer of changes induced by smoking.

LUNG REGENERATION IN ABSTAINING SMOKERS.

Smoking modifies morphological and physiological parameters of the lungs. Due to the irritation of airways, the natural self-cleaning ability of the lungs is impaired. The mucus accumulates in the airways and various infections develop, leading to chronic bronchitis. After the cessation of smoking, the lungs of the smoker start to heal and regenerate. Cilia in the lungs start to grow again and cleanse the lungs, thus reducing the risk of infection. The regeneration of the lungs takes a long time and depends on the degree of lung damage due to smoking. The aim of this study was to reconstruct the evolution of this regeneration process in chronic smokers by using the biological effects of radon and its decay products. Thus, radon in this study served as a tracer of changes induced by smoking.

RADIATION EXPOSURE OF THE POPULATION FROM 222Rn AND OTHER NATURAL RADIONUCLIDES AROUND MOCHOVCE NUCLEAR POWER PLANT, SLOVAKIA.

In this article, the effective dose to the population from natural sources of ionizing radiation in the vicinity of Mochovce nuclear power plant in Slovakia is presented. All major contributions to the effective dose were taken into account, including the contributions from gamma radiation of soil and rocks, cosmic radiation, and indoor and outdoor radon and thoron. On the basis of recent indoor radon measurements in Slovak cities and publicly available data about radon concentration in the soil air, a roughly linear relationship was found between these variables. Consequently, the annual effective dose from indoor radon and thoron was conservatively estimated. For the area of interest, a map of conservatively estimated potential effective doses was created. For the villages in the vicinity of Mochovce, the conservatively estimated effective dose to the population from natural sources ranged from 5.4 to 14.6 mSv, which is four orders of magnitude higher than the contribution of radioactive discharges from Mochovce nuclear power plant.

Simulation of radiation damage to lung cells after exposure to radon decay products.

OBJECTIVES: Exposure to radon and radon decay products represents one of the greatest risks of ionizing radiation from natural sources in some residential and working areas. Recently increasing attention has been paid to accurate estimations of this health risk by using various models. METHODS: In the presented study, a bystander model was used to predict biological effects of radon products on lung tissue target cells. The model considers radiation response as a superposition of the direct alpha particles hit effect and the bystander (cells communication) effect. Energy deposition in the lung tissue and in the air gap was calculated using the Bethe-Bloch equation. The exponential distribution of radon progenies in the mucous layer of smokers and non-smokers was evaluated. RESULTS: The excess relative risk value of lung cancer occurrence per unit exposure obtained in our study was ERR/WLM=0.0047 for smokers and ERR/WLM=0.0171 (taking into account the environment in radioactive ore mines) for non-smokers. Other published results give the average excess relative risk values per unit exposure in the dwellings for smokers ERR=0.050 per 100 Bq.m(-3) and for non-smokers ERR=0.198 per 100 B.qm(-3). Results presented in this study are in good agreement with the published epidemiological data on lung cancer incidence for mines and residential areas. CONCLUSIONS: The bystander model is suitable for radon risk prediction in dwellings and at workplaces (residential and working areas).