CAR-BORNE SURVEY OF NATURAL BACKGROUND GAMMA DOSE RATE IN ÇANAKKALE REGION, TURKEY S ¸. Turhan 1, *, I ˙ . H. Arıkan 2 , F.Og ˘uz 2 ,T. O ¨ zdemir 2 , B. Yu ¨cel 2 , A. Varinliog ˘lu 3 and A. Ko ¨se 3 1 Department of Physics, Faculty of Science and Letters, University of Nevsehir, 50300 Nevsehir, Turkey 2 Turkish Atomic Energy Authority, Eskis ¸ehir Road 9 km, Lodumlu 06530, Ankara 3 Çekmece Nuclear Research and Training Center, Yarımburgaz Mah., 34303 Halkalı-I ˙ stanbul, I ˙ stanbul, Turkey *Corresponding author: serefturhan63@gmail.com Received June 29 2010, revised December 5 2010, accepted December 27 2010 Natural background gamma radiation was measured along roads in the environs of Çanakkale region by using a car-borne spectrometer system with a plastic gamma radiation detector. In addition, activity concentrations of 238 U, 226 Ra, 232 Th and 40 K in soil samples from the Çanakkale region were determined by using a gamma spectrometer with an HPGe detector. A total of 92856 data of the background gamma dose rate were collected for the Çanakkale region. The background gamma dose rate of the Çanakkale region was mapped using ArcGIS software, applying the geostatistical inverse distance-weighted method. The average and population-weighted average of the gamma dose are 55.4 and 40.6 nGy h 21 , respectively. The corre- sponding average annual effective dose to the public ranged from 26.6 to 96.8 mSv. INTRODUCTION The external and internal exposure of human beings indoors and outdoors to ionising radiation occurs mainly from natural background radiation that emitted by terrestrial (primordial) radionuclides in the earth’s crust, such as 40 K, 238 U, 235 U and 232 Th, and their radioactive decay products as well as cos- mogenic radionuclides, such as 3 H, 7 Be, 14 C and 22 Na, that are produced by the interactions of cosmic ray particles incident on the earth’s atmos- phere with the nuclei of atmospheric constituents. The worldwide average annual exposure to natural radiation sources remains 2.4 mSv, which is approxi- mately 86 % of the radiation to humans (1) . The specific levels of the primordial radionuclides are related to the rock types, which depend mainly on local geological and geographical conditions, while the amount (or intensity) of cosmic radiation depends on the altitude and the latitude, as well as the stage of the solar cycle. For example, igneous rocks such as granite, andesite, basalt, etc. contain more 238 U, 232 Th and 40 K than sedimentary rocks except for shales and phosphate rocks, which have relatively high content of radionuclides (1) . Nowadays many studies have been conducted to determine the background levels of radionuclides in soils, which can be related to the absorbed gamma dose rate in air. In the last few decades, direct measurements of outdoor absorbed gamma dose rates in air have been performed in many countries of the world. The measured outdoor absorbed gamma dose rates in air vary from 10 to 200 nGy h 21 with an average of 59 nGy h 21(1) . Recently, a number of studies related to the spectrometric measurement of the activity concentrations of terres- trial radionuclides in soil and the direct measure- ment of the natural background gamma dose rate were carried out in Turkey (2 – 15) . The Çanakkale region is situated in the northwes- tern part of Turkey between the longitudes 25840 and 27830 0 E and the latitudes 39827 0 and 40845 0 N and has territory in both the Asian and European continents. The region spans an area of 9737 km 2 . It is divided into 12 districts as shown in Fig. 1. At the end of 2009, its population was 477.735. An earlier study related to outline of the geology of the Çanakkale (Dardanelles) indicates that metasedi- ments, chiefly marbles and schists, are cut by granite and covered unconformably by Tertiary strata, which include both sediments and volcanics (16) . Especially young granitic and volcanic rocks are widespread in the Kestanbol region of Ezine town (17) . Although a few studies were conducted to determine the radioactivity concentrations of the terrestrial radionuclides and assess the outdoor absorbed gamma dose rate for the Çanakkale region (17 – 19) , detailed data of the outdoor absorbed gamma dose rate and the corresponding annual effective dose are not available for this region. In this study, direct measurements of the outdoor absorbed gamma dose rate were carried out using car-borne spectrometer system with 5-l plastic gamma radiation detector as well as spectrometric measurement of the terrestrial radionuclides ( 238 U, 226 Ra, 232 Th and 40 K) in surface (0–5 cm) soil samples collected from this region using the # The Author 2011. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com Radiation Protection Dosimetry (2012), Vol. 148, No. 1, pp. 45–50 doi:10.1093/rpd/ncq593 Advance Access publication 28 February 2011 by guest on January 4, 2012 http://rpd.oxfordjournals.org/ Downloaded from