Natural radioactivity and their radiological effects for different types of rocks from Egypt Shaban Harb a , Abd El-Bast Abbady a , Abd El-Hadi El-Kamel b , Imran Issa Saleh c , Abdallah Ibrahim Abd El-Mageed b,n a Department of Physics, Faculty of Science, South Valley University, Egypt b Department of Physics, Faculty of Science, Assiut University, Egypt c Department of Physics, Faculty of Education, Aden University, Yemen article info Article history: Received 25 August 2011 Accepted 2 November 2011 Available online 7 November 2011 Keywords: Radioactivity Radiological effect Rocks Absorbed dose abstract The present work investigated the radioactivity level of the rocks samples collected from different sites in Egypt. Twenty one rocks samples were analyzed by gamma-ray spectrometry using NaI(Tl) detector with specially designed shield. The concentration of three natural radionuclides namely 226 Ra, 232 Th and 40 K has been determined and compared with chemical data obtained by XRF analysis. The results showed that these radionuclides were present in concentration ranges (3.4–99, 7.5–134 and 93–3382 Bq kg 1 ), (54.9–211.6, 20.71–170.5 and 2068–2344 Bq kg 1 ) and (13–106, 29.25–106.1 and 682–755 Bq kg 1 ) for gneiss, granite and basalt rocks, respectively, while the values were (7.5, 12.5 and 263.9 Bq kg 1 ) and (113, 148.5 and 1672 Bq kg 1 ) for 226 Ra, 232 Th and 40 K in sandstone and siltstone rocks, respectively. Also radium equivalent activity, total dose rates and external hazard index of the rocks samples under consideration were calculated. The results showed that granite rocks contain a high proportion of natural radioactive elements, while sandstone rocks have lesser radioactivity concentration compared with other types of rocks. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction Natural radioactivity is associated mainly to primordial radio- nuclides, including the elements belonging to the 238 U, 232 Th and 40 K series. The terrestrial background radiation is related to the type of rocks. The higher concentrations of uranium, thorium and potassium are associated with phosphate and granite rocks (Abbady, 2005; Nada, 2003; Nagdya, 2003). Recent studies have also demonstrated a high content of these elements in Calc- Silicate rocks (Santos et al., 2010). Radiological risk assessment resulting from radionuclides pre- sent in rocks and soil has become necessary to avoid exposure to ionizing radiation. This study aims to know the natural radioactivity for different type of rocks from Egypt and assess the radiological hazard resulting from them, using NaI(Tl) gamma-ray spectrometers. The absorbed dose rate, radium equivalent activities, external hazard index have been calculated based on guidelines provided by UNSCEAR (2008). 2. Experimental 2.1. Sampling and sample preparation A total of 21 rock samples have been collected randomly from different sites from Egypt. Fig. 1 shows the locations of samples. Rock samples were crushed to small pieces and grinded to be powder. Each samples were dried in an oven at 105 1C and sieved through a 100 mesh, which is the optimum size enriched in heavy mineral (Walley El-Dine et al., 2001). The samples were packed in plastic containers dimensions of 75 mm in diameter and 90 mm height. The samples were weighed and stored for a minimum period of one month to allow daughter products to come into radioactive equilibrium with their parents 226 Ra and 232 Th and then were counted for 12–24 h depending on the concentration of the radionuclides. 2.2. Experimental setup Each sample was measured with a gamma-ray spectrometer consisting of a NaI(Tl) setup and multichannel analyzer 8192 channel, with the following specifications: resolution (FWHM) at 1.33 MeV 60 Co is 60 keV—relative efficiency at 1.33 MeV 60 Co is 7.5%. The detector is shielded in a chamber of two layers starting Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/radphyschem Radiation Physics and Chemistry 0969-806X/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2011.11.005 n Corresponding author. Tel.: þ20 100493535; fax: þ20 882342708. E-mail address: mageed39@yahoo.com (A.I. Abd El-Mageed). Radiation Physics and Chemistry 81 (2012) 221–225