Soil radioactivity levels and radiation hazard assessment in the highlands of northern Jordan Ibrahim F. Al-Hamarneh * , Mohammad I. Awadallah Department of Applied Science, Prince Abdullah Bin Ghazi Faculty of Science and IT, Al-Balqa Applied University, Al-Salt 19117, Jordan article info Article history: Received 29 May 2008 Received in revised form 25 August 2008 Accepted 26 November 2008 Keywords: Soil radioactivity Gamma-ray spectrometry Activity concentrations Elemental concentrations Radiation hazard assessment Jordan abstract Determination of the natural radioactivity has been carried out, by means of gamma-ray spectrometry system, in surface soil samples collected from various geological formations in urban areas of the northern highlands of Jordan. These highlands, extending from Yarmouk River in the north to Wadi Wala in the south, form the agriculturally important regions of Jordan. Soils of the study region, at which about 70% of the total population of the country are living, mainly originated from limestones that are locally used in construction materials, making the evaluation of environmental radioactivity and estimating the current radiation hazards to the population an interesting issue. The total average concentrations of radionuclides 226 Ra, 238 U, 232 Th, and 40 K were 42.5, 49.9, 26.7, and 291.1 Bqkg 1 , respectively. Correla- tions made among these radionuclides prove the existence of secular equilibrium in the investigated soils. The total average absorbed dose rate in the study areas is found to be 51.5 nGyh 1 , whereas the annual effective dose equivalent has an average value of 63.2 mSv y 1 . The external and internal hazard indices, the radium equivalent activity, and the annual gonadal dose equivalent associated with the investigated soils do not exceed the permissible limits except for soils originated from phosphate rocks. Moreover, the radio-elemental concentrations of uranium, thorium and potassium, evaluated for the various geological features in the study areas were calculated to indicate whether relative depletion/ enrichment of radioisotopes had occurred. The results of the present study were discussed and compared with internationally recommended values. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction In addition to being the main source of continuous radiation exposure to human, soil acts as a medium of migration for transfer of radionuclides to the biological systems and hence, it is the basic indicator of radiological contamination in the environment. Moreover, the soil radioactivity is usually important for the purposes of establishing baseline data for future radiation impact assessment, radiation protection and exploration (Ramli et al., 2005). Various studies concerning radioactivity bound to soil were carried out in many countries, such as: Khatir et al. (1998), Tzortzis et al. (2003), Matiullah et al. (2004), Ramli et al. (2005), Veiga et al. (2006) and many others. Most of these studies were concentrated on natural sources as the natural radiation is the largest contributor to the external dose of the world population (UNSCEAR, 2000). These dose rates vary from one place to another depending upon the concentration of natural radionuclides like 238 U, 226 Ra, 232 Th and 40 K present in soil. These radionuclides pose exposure risks externally due to their gamma-ray emissions and internally due to radon and its progeny that emit alpha particles (UNSCEAR, 1988). Data on natural radionuclides are still very scarce in Jordan and the previous studies are limited to specific regions, radionuclides and/or geological formation (Ahmad et al., 1997; Al-Jundi, 2002; Al- Jundi et al., 2003, Al-Hamarneh et al., 2003, Al-Hamarneh, 2005, 2006; Awadallah and Arafah, 2006; Awadallah and Imran, 2007; Al- Jundi and Al-Tarazi, 2008; Al-Kharouf et al., 2008). Therefore, a comprehensive study with the objective to systematically measure the terrestrial gamma radiation and determine its contribution to the annual effective dose equivalent to the pop- ulation in Jordan is highly needed. The primary objective of the present study is to determine the concentrations of 40 K, 226 Ra, 238 U, and 232 Th in surface soil samples collected from various geological formations of the most populated cities in Jordan (Irbid, Mafraq, Ajloun, Jerash, Salt, Zarqa, Amman, and Madaba). Correlations among measured radionuclides were made to investigate the * Corresponding author. Tel.: þ962 777 489677; fax: þ962 53530462. E-mail addresses: hamarnehibrahim@yahoo.com, hamarneh@bau.edu.jo (I.F. Al-Hamarneh). Contents lists available at ScienceDirect Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas 1350-4487/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2008.11.005 Radiation Measurements 44 (2009) 102–110