【正文】 not pose a significant radiological hazard when used for construction of buildings. 1. Introduction The need for cement is so great. That it considered a basic industry. Workers exposed to cement or its raw materials for a long time especially in mines and at manufacturing sites as well as people, that spend about 80% of their time inside offices and homes (Mollah et al., 1986。 Paredes et al., 1987) result in exposure to cement or its raw materials being necessary reality so we should know the radioactivity for cement and its raw material. There are many types of cements according to the chemical position and hydraulic properties for each one. Portland cement is the most prevalent one. The contents of 226Ra, 232Th and 40K in raw and processed materials can vary considerably depending on their geological source and geochemical characteristics. Thus, the knowledge of radioactivity in these materials is important to estimate the radiological hazards on human health. The radiological impact from the natural radioactivity is due to radiation exposure of the 濰坊學院本科畢業(yè)論文 3 body by gammarays and irradiation of lung tissues from inhalation of radon and its progeny (Papastefanou et al., 1988). From the natural risk point of view, it is necessary to know the dose limits of public exposure and to measure the natural environmental radiation level provided by ground, air, water, foods, building interiors, etc., to estimate human exposure to natural radiation sources (UNSCEAR, 1988). Low level gammaray spectrometry is suitable for both qualitative and quantitative determinations of gammarayemitting nuclides in the environment (IAEA, 1989). The concentration of radioelements in building materials and its ponents are important in assessing population exposures, as most individuals spend 80% of their time indoors. The average indoor absorbed dose rate in air from terrestrial sources of radioactivity is estimated to be 70 nGy h?1. Indoors elevated external dose rates may arise from high activities of radionuclides in building materials (Zikovsky and Kennedy, 1992). Great attention has been paid to determining radionuclide concentrations in building materials in many countries (Amrani and Tahtat, 2020。 Rizzo et al., 2020。 Kumar et al., 2020。 Tzortzis et al., 2020). But information about the radioactivity of these materials in Egypt is limited. Knowledge of the occurrance and concentration of natural radioactivity in such important materials is essential for checking its quality in general and knowing its effect on the environment surrounding the cement producing factories in particular. Because of the global demand for cement as a building material, the present study aims to: (1) Assess natural radioactivity (226Ra, 232Th and 40K) in raw and final products used in the Assiut cement factory and other local factories in Egypt. (2) Calculate the radiological parameters (radium equivalent activity Raeq, level index Iγr, external hazard index Hex and absorbed dose rate) which is related to the external γdose rate. The results of concentration levels and radiation equivalent activities are pared with similar studies carried out in other countries. 2. Experimental technique . Sampling and sample preparation Fifty seven samples of raw materials and final products used in the Assiut cement factories were collected for investigation. Twenty five samples of raw materials were taken from (Limestone, Clay, Slag, Iron oxide, gypsum) which are all the raw material used in cement industry, 20 samples of final products were taken from Assiut cement (Portland, ElMohands, White, and Sulphate resistant cement ()). For parison with products from other factories, 8 samples were taken from the ordinary Portland cement from (Helwan, Qena, Elkawmya, Torra) and 4 samples were taken of white cement (Sinai and Helwan). Each sample, about 1kg in weight was washed in distilled water and dried in an oven at about 110 176。C to ensure that moisture is pletely removed, The samples were crushed, homogenized, and sieved through a 200 mesh, which is the optimum size to be enriched in heavy minerals. Weighted samples were placed in a polyethylene beaker, of 350cm3 volume. The beakers were pletely sealed for 4 weeks to reach secular equilibrium where the rate of decay of the radon daughters bees equal to that of the parent. This step is necessary to ensure that radon gas is confined within the volume and the daughters will also remain in the sample. . Instrumentation and calibration 濰坊學院本科畢業(yè)論文 4 Activity measurements were performed by gamma ray spectrometry, employing a 3″3″scintillation detector. The hermetically sealed assembly with a NaI(Tl) crystal is coupled to a PCMCA (Canberra Accuspes). Resolution % specified at the 662 keV peak of 137Cs. To reduce gamma ray background a cylindrical lead shield (100 mm thick) with a fixed bottom and movable cover shielded the detector. The lead shield contained an inner concentric cylinder of copper ( mm thick) to absorb lead Xrays. In order to determine the background distribution in the environment around the detector, an empty sealed beaker was counted in the same manner and in the same geometry as the samples. The measurement time of activity or background was 43 200 s. The background spectra were used to correct the peak area of gamma rays of measured isotopes. A dedicated software program (Genie 2020 from Canberra) analyzed each measured γray spectrum. 3. Conclusion The natural radionuclides 226Ra, 232Th and 40K were measured for raw materials and final products used in the Assiut cement factory in Upper Egypt and pared with the results in other countries. The activity concentration of 40K is lower than all corresponding values in ot