Evaluation of Natural Radioactivity in Selected Soil Samples from the Archaeological of Girsu City in

The specific activity of natural radionuclides in (18) soil samples collected from antiquities area of Girsu city in Dhi-Qar Governorate (31.0459863N, 46.2534257E) in southern Iraq have been studied and evaluated. Experimental results were obtained by using a gamma ray spectrometer analysis system consists of a scintillation detector Sodium Iodide activated by Thallium NaI(Tl) of (3"×3") crystal dimension at the laboratory of radiation detection and measurement in Science Collage, University of Kufa. The spectrometer has been calibrated for energy by acquiring a spectrum from four standard sources of gamma radiations supplied by spectrum techniques (LLC). The measuring time of all soil samples is (18000 seconds), it was found that, for Girsu city the soil specific activity ranges from (22.68±3.94 to 14.69±2.24) Bq/kg for 146 23892 U , from (17.41±2.23 to 11.23±2.34) Bq/kg for 142 23290 Th and from (346.49±10.68 to 266.96±10.55) Bq/kg for 21 4019 K . The results have been compared with the acceptable data of the worldwide literatures. In order to evaluate the radiological hazard of the natural radioactivity, the radium equivalent activity (Ra eq ), the gamma absorbed dose rate (D), the annual effective dose rate and the both (external and internal) hazard index have been calculated and compared with the acceptable values of the worldwide average (UNSCEAR, 2000).


INTRODUCTION
atural radioactivity is present in the human environment due to the presence of Cosmogenic and primordial radionuclides in the Earth's crust [1] . Cosmogenic radionuclides are produced by the interaction of cosmic-rays with atomic nuclei in the atmosphere, while primordial ones (terrestrial background radiation) were formed by the process of nucleo-synthesis [2] . Only those radionuclides with half-lives comparable to the age of the Earth, e.g., Th series, can still be found today in different geological materials [3] . Natural Occurring Radionuclides Materials (NORM) is known to be present in rocks and soil. Specific levels of terrestrial background radiation mainly depend on the geological and geographical conditions [4,5] . Scientific motivation for this study is based on measuring concentrations and distributions of natural radionuclides    (1). The samples were ground into a fine powder with a particle size less than 100 μm and then dried in a temperature-controlled furnace at (110 °C) for (24 h) to remove moisture. Each sample stored in a sealed polyethylene marinelli beaker for 30 days to achieve the secular equilibrium. This marinelli beaker was used as sampling and measuring container. Before use the containers were washed with hydrochloric acid and rinsed with distilled water [7] .
The activities of natural radionuclides The activity concentration of each radionuclide was calculated by the following equation [8] : Where A is the activity concentration of the radionuclides (Bq/kg), C is the count rate, ε is the detector efficiency for the specific gamma-ray energy, I γ is the absolute transition probability of gamma decay, m is the mass of sample (kg) and t is the counting time in second. Exposure radiation has been defined in terms of radium equivalent activity Ra eq in (Bq/kg) to compare the specific activity of materials containing different amounts of 19 K in soil are not uniform, The radium equivalent activity can be calculated using the following relation [9] : 19 K produce the same gamma dose rate [10] .
The external gamma absorbed dose rate in the air at (1 m can be neglected as they contribute very little to the total dose from environmental background [11] . The calculations were performed according to the following equation [9] : Where D is the dose rate in (nGy/h). The external hazard index, H ex , is defined as [10] : There is another hazard index called internal hazard index H in , which is determined as follows [10] : The value of this index must be less than unity in order to keep the radiation hazard insignificant. The maximum value of H ex and H in equal to unity corresponds to the upper limit of radium equivalent activity (370Bq/kg).
To estimate the annual effective dose, the following must be taken into consideration [12] : (a) The conversion coefficient of absorbed dose in air to effective dose. (b) The indoor occupancy factor. Using the dose rate data obtained from the concentration values of natural radionuclides in soil, adopting the conversion factor of (0.7 Sv/Gy) [8] from absorbed dose rate in air to effective dose received by adults and considering that people in Girsu city, on the average, spent (20%) of their time outdoors, the annual effective doses are calculated [8] : Outdoor annual effective dose (Sv) = D × 24 × 365 × 0.7 × 0.20 ... (6) Indoor annual effective dose (Sv) = D × 24 × 365 × 0.7 × 0.80 …. (7) Also the Elemental concentrations were determined by using the relation between the specific activity and the Elemental concentrations as shown in the   [13] . The Radium equivalent activities are calculated and listed in table (2), Ra eq values vary from (53.88±6.23 to 70.89±7.75) Bq/kg with an average value of (63.66±7.26) Bq/kg. It can seen be that the Ra eq values for all soil samples are lower than the recommended maximum value (370Bq/kg) [13] .
The absorbed dose rate one meter above the ground, indoor and outdoor annual effective dose for Girsu city samples were calculated and given in table (3). The result shows that the highest value is (33.96 nGy/h), whereas the lowest value is (26.01 nGy/h) and the average value (30.55 nGy/h). The values of absorbed dose rate for soil sample under limit the worldwide average value (55 nGy/h) [14] . In addition, the calculated values of absorbed dose rate were given in table (3) and as well as, the values of indoor and outdoor annual effective dose were calculated ranged from (0.127 to 0.166 mSv/y) and from (0.023 to 0.042 mSv/y) respectively. The average values of annual indoor and outdoor effective dose are (0.149 and 0.037 mSv/y) respectively. All values of indoor and outdoor annual effective dose were less than (1

Evaluation of Natural Radioactivity in Selected Soil Samples from the Archaeological of Girsu
City in Dhi-Qar Governorate, Iraq 3125 mSv/y) recommended by International Commission on Radiological Protection (ICRP 1993) [14] .  (4). In this table, one can see that the values of external hazard index have been found to lie in the range of (0.145 to 0.191) with an average of (0.172). In concern with the minimum value of internal hazard index is (0.185) and the maximum value is (0.251) with an average of (0.223).
Generally the concentrations of (     [14] . The activity levels due to terrestrial background radiation are related to the type of rock from which the soil originates. As regard of activity with respect to depth, no correlation was found between activity and depth. The measured values of radioactivity show that it is randomly distributed in different depth of the soil. The selected spectra of some soil samples from this region are shown in figure (2).

CONCLUSIONS
The environmental monitoring of natural background radiation using Sodium Iodide NaI(Tl) detector revealed the distribution of the natural radiation levels in all the soil samples measured. From the obtained result, one could see that the distribution was not uniform. Also artificial radionuclide was not detected in any of the measured samples. The obtained results confirm some conclusions as below: 1-The present work has shown that the radioactivity concentration of 5-The estimated average absorbed dose rates in air for the studied area are below or comparable with world average (55nGy/h). 6-All average values of annual indoor and outdoor effective dose were lower than the permissible limit. 7-The gamma-ray spectrometry is a good technique for measuring natural radioactivity in soil. 8-The measured values of radioactivity show that they are randomly distributed with depth.