Radiation of mining grounds - case study forecasting the hazard level of ionizing

When analyzing time series we can often observe that they have periodic oscillations (cyclic, seasonal). One of the methods which can be applied to investigate such a phenomenon and which belongs to the group of periodic components models is the method of harmonic analysis. The method consists in analyzing the oscillations around the medium level a0 and building a model as the sum of so called harmonics. The paper presents the applicability potential of harmonic analysis in the forecasting process of radiation hazard on post-mining grounds (mine waters with raised content of radium Ra226 and Ra-228 drained off to the surface), using for that purpose the measurement results of radium concentration from the area of mine water catchment from the years 2004-2013. RADIATION ON MINING GROUNDS – CASE STUDY FORECASTING THE HAZARD LEVEL OF IONISING INTRODUCTION Ionizing radiation is one of the most characteristic phenomenon connected with atomic transitions taking place in atoms and in the atomic nucleus. The phenomenon consists in the separation of elementary negative charges (electrons) from atoms, which brings about the formation of the pairs of positive ions and electrons. The occurrence of ionizing radiation hazards is attributed to the presence of natural radioactive isotopes and cosmic radiation (radiation generated by the sun and galactic radiation) [4, 8]. Generally, we can distinguish three basic hazard sources:  natural radioactive isotopes present in the Earth’s crust,  secondary cosmic radiation,  radon and its decomposition products. It is estimated that, statistically, within one year everybody is exposed to the radiation doze of around 2.0 mSv (in the member countries of the European Union the average doze generated by natural sources is at the level of around 3.0 mSv, and in Poland – 2.2 mSv) [3]. The radiation hazard posed by natural radioactive substances is classified into a group of natural hazards, whereof the sources are as follows:  short-lived decomposition products of radon,  gamma radiation containing radium,  mine waters containing radium isotopes,  sediments containing radium isotopes precipitated from mine waters containing radium. The concentration of the potential energy of short-lived decomposition products of radon depends principally on the aeration method and extraction of the deposit. The concentration of radium in waters is increasing with depth (the salinity of waters is increasing then, which is a decisive factor), and the occurrence of radioactive sediments is connected with the presence of barium (from such waters, radioactive sediments can precipitate at places where radium waters of the A type are getting mixed with waters containing sulphates) [10]. Due to the specific work environment (enclosed space, limited ventilation, etc.) the concentration of radium isotopes underground can several times surpass the concentration of radium in the open space (150 kB/m in the coal mines of the Lower Silesia Coal Basin, 15 kBq/m in the coal mines of the Upper Silesia Coal Basin and on average 8 B/m in the open spaces [9]). According to the executive regulations of the Geological and Mining Law, all underground mining plants in Poland are supposed to carry out periodic measurements of radiation hazard posed by natural radioactive substances. Only in 2007, coal mines carried out over 2900 measurements involving the concentration of potential energy of shortlived decomposition products of radon, 123 measurements of individual dozes of gamma radiation, 390 analyses involving the radioactivity of mine waters and 141 analyses of mine sediment samples. In compliance with the Regulation of the Minister of Economy on the occupational health and safety, mining activity and specialist fire protection equipment at underground mining plants, it is not acceptable that in a given year the hazard effected by natural radioactive substances in a coal mine should be higher than 20 mSv: underground workings being in the radiation hazard class B (workings in which the work environment creates potential hazard of being exposed to an yearly effective doze higher than 1mSv and not higher than 6 mSv) are treated as supervised workings, and the workings assigned Zygmunt KORBAN Silesian University of Technology