Radiation Hazard Assessment by Measuring of Soil Radioactivity Levels in Al-anbar (Al-fallujah District) and Wasit Governorate in Iraq

Soil samples were collected from two region Al-anbar (Al-fallujah district) and Wasit of Iraq with an aim to determine the activity concentration using a coaxial high purity germanium (HPGe) detector based on high-resolution gamma spectrometry system. 226 Ra, 232 Th, the primordial radionuclide 40 K, and the artificial radionuclide 137 Cs were measured in the soil of the study area. The mean radioactivity concentration in Al-anbar (Al-fallujah district) and Wasit region due to 226 Ra, 232 Th, 40 K, and 137 Cs was (20.36, 11.08, 226.97, and 1.01Bq kg -1 ) and (23.01, 14.45, 290.64, and 2.22 Bq kg -1 ), respectively. Radium equivalent activity (Raeq), representative level index (Iγ), absorbed gamma dose rate (D) in air, total annual effective dose equivalent (AEDE) from the terrestrial gamma radiation, the external and internal hazard index were estimated. The mean of six hazard index values came out to be (53.67Bq kg -1 , 0.38Bq kg -1 , 24.78Bq kg -1 , 0.15mSv y -1 , 0.14Bq kg -1 , and 0.19Bq kg -1 ) in Alanbar (Al-fallujah district) and (66.17Bq kg -1 , 0.49 Bq kg -1 , 32.08 Bq kg -1 , 0.2mSv y -1 , 0.18 Bq kg -1 , and 0.24 Bq kg -1 ) in Wasit, respectively. Present data have been compared with the published data for other regions of the world near from the study area and found to be safe for public and environment.


Introduction
Human beings have always been exposed to natural radiations arising from within and outside the earth. The primordial radionuclides have radioactive decay half-lives that are approximately earth's age. The exposure to ionizing radiations from natural sources occurs because of the naturally occurring radioactive elements in the soil and rocks, cosmic rays entering the earth's atmosphere from outer space and the internal exposure through incorporation of these radionuclides into the body by inhalation or ingestion. These radionuclides and their radioactive decay products are an important source of earth's radioactivity [1,2]. The natural radioactivity in soil primarily comes from 238 U and 232 Th series and natural 40 K. Artificial radionuclides can also be present such a 137 Cs, resulting from fallout from weapons testing and from accidents such as Chernobyl. The radiological implication of these radionuclides is due to the gamma ray exposure of the body and irradiation of lung tissue from inhalation of radon and its daughters. The great number of decay products of 238 U and 232 Th series and 40 K are the main components of external gamma radiation originating from soil. Therefore, the assessment of gamma radiation dose from natural sources is of particular importance as natural radiation is the largest contributor to the external dose of the world population [1]. The average annual radiation dose to world population is 2.8 mSv approximately 85% (2.4 mSv) of this comes from natural radionuclides of both terrestrial and cosmogenic origin [3]. 137 Cs is regarded as the most important constituent of worldwide radioactive fallout. Sixty percent of the collective effective dose equivalent commitment from external radiation associated with past atmospheric nuclear weapon testing may be attributed to 137 Cs. In the case of an accidental release of fission products from a nuclear power plant, cesium isotopes are especially significant due to their volatility and large inventory that builds up in the reactor over time. Therefore, measurement of 137 Cs levels in soil is necessary in the environment of a studied area as such a data would serve as the baseline data. Its presence in soil would be an indicator that the area under study might have received some fallout radioactivity in the past [4]. The specific levels are related to the types of rock from which the soils originate. Higher radiation levels are associated with igneous rocks, such as granite, and lower levels with sedimentary rocks [1]. The present study deals with the measurement of specific activities of 226 Ra, 232 Th, 40 K and 137 Cs, calculation of the radium equivalent activity, external and internal hazard indices, absorbed dose and annual effective dose equivalent for the studied area. This data will help to decide whether the studied region is in an area of normal or high background radiation and will set a baseline for the determination of radioactivity level in the region [4].

Description of Study Area
Soil sampling was carried out in 2011. The geological locate of the two governorate Al-anbar (Al-fallujah district) and Wasit at west and middle of Iraq. Soil samples were collected from three selected sites at Al-anbar (Al-fallujah district) governorate and six selected sites at Wasit governorate, which were chosen for two reasons: first record rise in cancers and birth defects rates in the surrounding residential areas of sites according to the information that has been obtained from hospital near the sites or from the governorate council and the second that these areas have seen some of them military operations were reconstruction and other division is the remnants of the wreckage of vehicles and wheels military destroyer and some rubble of buildings. The description of the study area has been reported elsewhere in reference [5]. Tables 1 & 2 were shown the description of the study area at Al-anbar (Al-fallujah district) and Wasit governorate respectively while Figure 1 was shown the soil sampling locations on map of Al-anbar (Al-fallujah district) and Wasit governorate respectively.

Sample Preparation
At each site, samples were taken from layer down to 25 cm depth. Fine quality of the sample was obtained using sieve of 9 mesh size (2 mm particle size). An average 0.5 kg of soil was used per sample. Before measurement samples were dried in an oven at a temperature of 80°C for 8 hr. These samples were packed and sealed in a marinelli beaker and kept for about 3 week period to allow radioactive equilibrium among the daughter products of radon, thoron and their short lived decay products [6].

Sample Analysis
The samples were analyzed at MOST Gamma Ray Spectrometry laboratory. Using high-resolution gamma spectrometry system consists of coaxial High Purity Germanium (HPGe) detector. The detector has resolution of 2.0 keV and relative efficiency of 40% for 1.33 MeV gamma energy of Co-60. The detector was shield with lead of thickness 10 cm and internally lined with 3 mm copper to reduce the environmental gamma background radiation. The efficiency calibration of the system was employed by reference materials. The gamma ray spectrum was recorded using software GENIE-2000. 226 Ra was assessed through the photo peaks of its daughters: 214 Pb (352 keV) and 214 Bi (609keV) furthermore the concentration of 232 Th was determined through the photo peaks of 228 Ac (911keV) and 212 Pb (238.6 keV). 40 K and 137 Cs were measured directly from their 1460.8, 662 keV gamma ray peaks [5].

Radium Equivalent Activity
To represent their specific activities levels of 226 Ra, 232 Th, and 40 K by a single quantity which take into calculation the radiation hazards related with them, a common radiological index has been used which is radium equivalent (Ra eq ). To define Ra eq activity, it can be assumed that 1 Bq/kg of 226 Ra, 0.7 Bq/kg of 232 Th or 13 Bq/kg of 40 K give the same dose of gamma ray.

Representative Level Index (I γ )
The representative level index (I γ ) used for the calculation of gamma radiation associated with the natural radioactive materials in the soil. It is calculated using Eq. (2). The safety value for this index is 1 [8 & 9]

Air Absorbed Radiation Dose Rate
Adsorbed dose rate in air at a height of about 1 meter above the ground surface due to gamma radiations for uniform distribution of the naturally occurring radionuclides 226 Ra, 232 Th and 40 K is calculated using Eq. (3). The conversion factor of 0.462 nGy h -1 /Bq kg -1 for 226 Ra, 0.621 nGy h -1 /Bq kg -1 for 232 Th, 0.0417 nGy h -1 /Bq kg -1 for 40 K, and 0.136 nGy h -1 /Bq kg -1 for 137 Cs equilibrium is assumed between 226 Ra and 232 Th series with all their daughter and the effect of 90 Sr and 235 U decay series can be neglected because of their small contribution to the whole dose from background. [4 & 7] !nGy h & ' 0.462 + 0.621 + 0.0417 + 0.136 *

Annual Effective Dose Rate
The annual effective dose rates expected to be received by the general public due to the radioactivity in soil was calculated using Eq. (4 & 5) the conversion coefficient from absorbed dose rate in air to effective dose (0.7 Sv Gy -1 ) and an outdoor occupancy factor (20%) proposed by UNSCEAR 2000 are used [1,4,7].

External and Internal Hazard Index [9 & 10]
The external hazard index (H ex ) is widely used to reflect to external exposure and can be calculated by Eq. (6): In addition to the external hazard index, radon and its short-lived products are also hazardous to the respiratory organs. The internal hazard indexes (H in ) used to reflect to internal exposure to radon and its daughter, which is given by Eq. (7): The values of the indices of external and internal radiation hazard index must be less than unity for the radiation hazard to be negligible.

Results and Discussion
The data in Table (3 & 4) are summarized of measurements of natural and manmade radionuclide ( 226 Ra, 232 Th, 40 K, and 137 Cs) concentration and radium equivalent in the collected soil samples from Al-anbar (Al-fallujah district) and Wasit governorate, respectively. The mean activity concentration at Al-anbar (Al-fallujah district) due to 226 Ra, 232 Th, 40 K, and 137 Cs was 20.36, 11.08, 226.84, and 1.01Bq kg -1 , respectively. In Wasit governorate, the mean activity concentration due to 226 Ra, 232 Th, 40 K, and 137 Cs was 23.01, 14.54, 290.64, and 2.22Bq kg -1 , respectively. 137 Cs concentration was detected very low at most of the places. Its concentration at Al-anbar (Al-fallujah district) governorate ranged from 0.00 to 2.3Bq kg -1 with an average value of 1.01 Bq kg -1 and at Wasit governorate was ranged from 0.70 to 5.06 Bq kg -1 with an average value of 2.22 Bq kg -1 and these concentration survey low at most of the places for that they don't have any radiological important. The activity concentration of 226 Ra, 232 Th, and 40 K in soil samples of studied area was compared with the value reported by other countries near from study area as shown in Table (5). The measured activity concentration of 226 Ra and 232 Th was close to the Syria and Iran for Al-anbar (Al-fallujah district) and Wasit. While the measured activity concentration of 40 K was closed to Southern Jordan and Syria for two governorates. Furthermore, the world average concentrations for 226 Ra, 232 Th, and 40 K in soil sample are 35, 30, 400 Bq/kg, respectively [7].   Radium equivalent activity (Ra eq ) in Bqkg -1 for these soil samples were shown in Table 3 and 4. The mean radium equivalent activity in Al-anbar (Al-fallujah district) is 53.67 and in Wasit is 66.17 Bq kg -1 which is less than the safe limit (370 Bq kg -1 ) recommended by Organization for Economic Cooperation and Development [7].
Tables (6) and (7) were shown the five radiation hazard indices for soil samples for Al-anbar (Al-fallujah district) and Wasit governorate, respectively. The values of representative level index (Iγ) of soil samples ranged from 0.26 to 0.48 Bq kg -1 with a mean value of 0.38 Bq kg -1 for Al-anbar (Alfallujah district)governorate and ranged from 0.3 to 0.7 Bq kg -1 with a mean value of 0.49 Bq kg -1 for Wasit governorate. All values were lower the unity permissible limit. Equations (3, 4, and 5) were used to calculate the absorbed dose rate !nGy h & ' and the effective dose rate !/01 2 ⁄ ' in outdoor and indoor air for Al-anbar (Al-fallujah district) and Wasit governorate, as shown in Tables (6) and (7) [7].
All calculated values of the effective dose rate for two governorates are far lower than the 1.0 mSv.y -1 recommended by UNSCEAR 2000. Furthermore the calculated values are near from the values which were calculated in the previous study [9] using ReCLAIM program version 3.0 as shown in Figures (2 and 3) for Al-anbar (Al-fallujah district) and Wasit governorate, respectively.

Conclusions
1. The measured activity concentration of 226 Ra and 232 Th was close to the Syria and Iran for Al-anbar (Al-fallujah district) and Wasit while the measured activity concentration of 40 K was closed to Southern Jordan and Syria for two governorates. Furthermore, the world average concentrations for 226 Ra, 232 Th, and 40 K in soil sample are 35, 30, 400 Bq/kg respectively. 2. 137 Cs concentration was detected very low at most of the places. Its concentration at Al-anbar (Al-fallujah district) governorate ranged from 0.00 to 2.3Bq kg -1 with an average value of 1.01 Bq kg -1 and at Wasit governorate was ranged from 0.70 to 5.06 Bq kg -1 with an average value of 2.22 Bq kg -1 and these concentration survey low at most of the places for that they don't have any radiological important 3. The results obtained have shown that the effective dose rate values due to natural radioactivity of soil samples are far lower than the average world recommended value of 1.0 mSv.y -1 and near from the values were calculated using ReCLAIM program version 3.0.