Natural radioactivity concentration in raw materials used for manufacturing refractory products

Many materials that are usually found in the earth's crust contain small but measurable amount of naturally occurring radioactivity (NORM). Some particular ores contain natural radionuclide at levels much higher those usually present in earth's crust; and are also subject to radioisotope enrichment, during technological process, known as technologically enhanced natural radioactivity (TENORM). The term TENORM was proposed to distinguish the NORM from that enhanced by technological process. Typical concentrations of U and Th in the earth's crust and in various natural materials are compared in table 1 (1-3). The investigations of zirconium ores as sources of TENORM began in the late 1970s, and early 1980s (4, 5). These works highlighted the relatively high concentrations of natural radionuclide in zircon ores. Zirconium silicate (ZrSiO4) is the most important compounds obtained from zircon sand; baddeleyite is a natural form of zirconium (ZrO2). The most important applications of zircon sands are as refractories, foundry sands and ceramic opacifiers. At present, South Africa, Ukraine, India, Brazil and China are the largest exporters of zirconium materials (6). In Iran, zirconium minerals are widely used in ceramic industry. This sector absorbed about 700 tons (1999-2001) of zircon, principally for opacifier. Iran imports zirconium sands from South Africa, Italy, Ukraine, and to lesser extent, from Germany and Belgium. Radiation dose limits for exposure of Iranian workers is 100 mSv in a period of 5 consecutive years, with a maximum dose of 20 mSv in one year. For the population, the dose limit is 1 mSv y-1 (7). The internal exposure, through inhalation, and external exposure are the main radiological concern about zirconium applications. Gamma radiation dose rate close to bulk quantities of zirconium sands Background: Some Particular areas contain natural radionuclide at levels much higher than those usually present in earth's crust. The radiological impact of the use of zirconium ore in zirconium industry is due to internal exposure of the lung by alpha particles and external exposure of the body by the gamma rays. The result of gamma spectrometry measurement of the concentrations of the natural radionuclide in zirconium industry is described. Materials and Methods: Gamma spectrometry system with a shielded high pure germanium (HPGe) detector connected to multi channel analyzer (MCA) was used to determine concentrations of natural radionuclide in about 45 samples of imported zirconium minerals, tiles, stone ware and waste sludge's of Iranian ceramic industry. Results: The U concentration in the samples, ranging from 3000 to 10000 Bq Kg, is higher than the concentration of both Th (500-1800 Bq Kg), and K (50-800 Bq Kg). The measured specific activities in the mineral showed that specific activity of baddeleyite is higher than that of zircon. The results of ceramic tiles show that the tiles usually contain small amount of zirconium compound. Conclusion: Due to relatively high concentration level of uranium in imported zirconium samples, specific regulations is necessary for zirconium compound used in ceramic industry. Iran. J. Radiat. Res., 2007; 4 (4): 201-204