The Measurements of Natural Radioactivity , ( Radon and Gamma concentrations ) , around the old fertilizer factory in Basrah / Iraq

Radon concentration, exhalation rate, annual effective dose, radium activity, thorium, uranium potassium and radium equivalent have been measured in the present investigation for soil in the area around the old fertilizer factory in southern of Basrah Governorate. The measurements based on CR39 track detector for passive method, RAD7 for active method and NaI(Tl) for gamma concentration measurements. Average values for radon concentration in soil were 112.04±10.76 Bq/m 3 using passive technique and 104.56±6.05 Bq/m 3 using RAD7. From the result of the passive technique, area and mass exhalation rates and the annual effective dose were calculated. Gamma ray spectroscopy for the soil samples were performed and found that the average concentrations of 226 Ra, 232 Th and 40 K were 50.89 Bq/kg, 21.74 Bq/kg and 640.4 Bq/kg respectively. Gamma ray hazard indices were calculated and found they are within the world average.


INTRODUCTION
It is widely known that, high radon concentration and its daughters are dangerous to human health. Radon is an odourless, colourless and tasteless gas and it is the second cause of lung cancer after smoking. The assessment of radon in soil and building materials helps to understand and minimized such effects. Soil is the prime source of radium (t1/2=1600y), parents of radon gas. The natural abundance of radon gas consists mainly two isotopes; 222 Rn t1/2=3.82 d and 220 Rn t1/2=56s. The concentration of radon is soil varies in different quantities according to geological structure of the place, because radon is chemically unreactive, it freely to moves between particles and rocks. In some cases radon trapped in certain places and creates area of highly concentration of radon gas, called radon prone area [1]. The radon exposure is considered mostly as internal exposure, because it is dynamic gas. Gamma radiation from natural radionuclides and cosmic rays constitute as external exposure to humans. The radionuclides of concern in terrestrial environment are mainly potassium 40 K, radium 226,228 Ra, uranium 238 U and 232 Th [2][3][4][5]. Natural radio activities is widely spread in the earth's environment and depends primarily on the geological and geographical condition, and appear at different level in the soil of each region of the world [UNSCEAR 2000].
In the present work, sealed can technique is used for radon measurements, together with NaI(Tl) for gamma ray measurement.

A. PASSIVE RECHNIQUE
Fifty two soil samples were collected from different location in the selected study area shown in Figure 1. Sealed can, 30 cm x 7.5 cm, technique was used for passive measurements [6]. The cans, with CR39 detectors stuck on the bottom of the tope cover, have been stored for 3

Figure 1 area of study around the fertilizer factory
months for irradiation process. The tracks were observed after etching and counted by using microscope with a magnification of 400x. The etching conditions were: 6.25N sodium hydroxide at 70 o C for 8 hours. The track density and radon gas activity was obtained through calibration factor of K=0.2857±0.01431 Tr cm -2 d -1 per Bq m -3 according to the relation [6] Radongasconcentrationis givenby [7]; where is track density in Tr/cm 2 , t exposure time in day and K the calibration factor in Tr/cm 2 .day / Bq.m -3 . At the equilibrium state, final activity of radon exhalation from each sample inside the can is given by [8][9] = / + −1 − −1 (2) where Ex is exhalation rate in unit Bq m -2 .h -1 , A is radon concentration measured by CR39 detector in unit Bq m -3 , is radon decay constant, T is the exposure time, V the volume of the can and S is the surface area of the sample.
The radon exhalation rate in terms of mass is calculated from the relation; D e c e m b e r 2 9 , 2 0 1 4 where EM expressed in Bq kg -1 h -1 and M is the mass of the sample measured in kg.
The annual effective dose equivalent to potential alpha energy Ep is given to the following formula: where n is occupation number estimated as n=0.8 indoor and n=0.2, is radon equilibrium factor estimated as F=0.41 and ARn is the measured radon gas concentration [10]

B. THE ACTIVE TECHNIQUE
A radon gas analyser RAD7 instrument (DURRIDGE Company USA) was used to measure radon emanation from soil samples. The soil sample was loaded into 1.32 used as an emanation cylindrical container. The high of the container 30 cm, to insure radon detection only, was connected online with RAD7 instrument. To reduce the influence of humidity on the radon detection and measurements, the system purged for 10-15 minutes to reduce the humidity to less than 10% [11]. The alpha RAD7 detector was operated in grab mode for 2days protocol, with cycle 1h and recycle 48.

GAMMA RAY SPECTROSCOPY
The gamma ray spectroscopy used in this work consist of highly shield and well calibrated 3"x3" NaI(Tl) detector enclosed in 5 cm thickness lead shielding for background reduction. The system consist of computer based multichannel analyser for date acquisition and software to controls these data acquisitions, supplied by manufacturer. The spectrometer was calibrated with 57 Co, 60 Co and 137 Cs slandered sources. The background was counted for, by counting with empty Merelani beaker for 9000 s.
After measuring the count rate (area under the peak) for each peak and subtract the background, the activity concentration for each environmental isotope calculated from [12] = × × × (5) where ε is absolute gamma peak efficiency of the detector at this particular gamma-ray energy, decay intensity for the specific energy peak (including the decay branching ratio information), M the mass of the sample in kg and t is the counting time of the measurement in second.
Radium equivalent activity (Raeq) is used to assess the hazards associated with materials that contain 226 Ra, 232 Th and 40 K in Bq kg -1 , which is, determined by assuming that 370 Bq kg -1 of 226 Ra or 260 Bq kg -1 of 232 Th or 4810 Bq kg -1 of 40 K produce the same γ dose rate. The Raeqof a sample in (Bq kg -1 ) can be achieved using the following relation [13]; The published maximal permissible Raeqis 370 Bq kg -1 [14].
The external and internal hazard indices are an evaluation of the hazard of the natural gamma radiation. The prime objective of this index is to limit the radiation dose to the admissible permissible dose equivalent limit around 1mSvy −1 . In order to evaluate this index, one can use the fallowing relations [13] = ( 370) + ( ℎ 259) + ( 4810) = ( 185) + ( ℎ 259) + ( 4810) This model takes into consideration that the external hazard which is caused by gamma-rays corresponds to a maximum radium-equivalent activity of 370 Bq/kg for the soil.
In order to estimate the annual effective dose rate in air, the conversion coefficient from absorbed dose in air to effective dose received by an adult must be considered. This value is published in UNSCEAR 2000 and UNSCEAR 1993, to be 0.7 SvGy -1 for environmental exposure to gamma rays of moderate energy. The outdoor occupancy factor is about 0.2 . The annual effective dose equivalent is given by the following equation [13]; where ℎ = 0.0417 + 0.462 + 0.606 ℎ The world average annual effective dose equivalent (AEDE) from outdoor or indoor terrestrial gamma radiation only is 0.560 mSv/year [UNSCEAR].

RADON RESULTS
The activity concentration of radon emanated from soil and river sediment are presented in Table 1 Figure 2, where the correlation is very strong, correlation factor R=100%. Radon concentration from animal manure is 63.6±7.1 Bq/m 3 and 29.4±4.4Bq/m 3 , which is relatively low concentration. The radon concentration in Shellfish sample found to be 62.4±7.0 Bq/m 3 , which is also relatively low. In general, all the radon concentrations were low in compare with surrounding areas.   Radon is well known to be a good contributor toward the natural absorption radiation dose, and the total effective dose of natural radioactivity is 2.5 -3 mSv/y and 56% from this dose is related to radon, which approximately equal to 1.4 mSv/y. The maximum value of the effective dose from the studied samples was found to be 0.1799 mSv/y, which is far smaller than the warning level. The recommendation of the ICRP 2011 [15] is that, the action level of indoor radon should be set within a range of 3 -10 mSv/y.

GAMMA SPECTROSCOPY RESULTS
Radionuclide activity concentration in soil samples were measured and listed in Table 3. The results contain specific activity concentration as well as the uncertainty of 226 Ra and 232 Th and 40 K. The range of 226 Ra in all the studied samples varies from 21.550±1.400 Bq/kg to 82.89±5.69 Bq/kg with mean value of 50.888±3.436 Bq/kg, which is closed to the allowed safe limit 50 Bq/kg [16]. The specific concentration of 232 Th has a range between 7.410±0.550 Bq/kg to 39.520±2.950 Bq/kg with the mean value of 21.741 Bq/kg, which is less than 50 Bq/kg (UNSEAR prediction) for safe area. The specific concentration of 40 K ranges from 323.750±1.420 Bq/kg to 1111.220±4.870 Bq/kg with arithmetic mean value equal to 640.434±2.804 Bq/kg, which is more than the world average value of 500 Bq/kg [16] Table 4 presented the calculated gamma indies using equations (6)(7)(8)(9)(10), the radium equivalent activity Raeq has a range from 62.37 Bq/kg to 201.63 Bq/kg and average of 130.96 Bq/kg, which is less than the UNSCEAR, adopted limit 370 Bq/kg. The values of external and internal hazard are less unity in all samples, as recommended. The average values for outdoor and indoor effective dose are 0.077 mSv/y, 0.370 mSv/y and this also less than 0.56 mSv/y recommended by UNSCEAR. Figure 3, shows the correlation between 226 Ra concentrations measured by gamma ray spectroscopy and 222 Rn measured by passive method. The correlation looks positive and strong, correlation factor R=0.92%. Ra and 232 Th concentrations which shows a positive with intermediate correlation R=64. However, the correlation between these isotopes is not necessarily, because their concentrations depend on the geological structure of the area which is random. The second figure, on the right, presents a graph between 226 Ra and 40 K , which is show a week correlation R= 22%.


The measurements indicate normal level of radon exhalation from soil samples in the studied area. The average value of radon concentration, area and mass exhalation rates are found to be significantly lower than the current results of the world wide measurements of radon concentration and exhalation rate. This range is considered within the safe limits of international radiation committees.


The investigation results clearly show that the area is safe as far as the health hazard of radon is concerned.


The positive and strong correlations between active and passive measurements of radon concentrations in soil samples gives us indications that, it is possible to depend on the electronics instrument RAD7 in the investigation of radon concentration in soil (faster and precise).
 A strong correlation between radium and radon concentrations was found


Week correlation between radium and thorium and potassium was found  The results of radon and gamma concentrations reveal that the area is safe for human activities as far as the effect of radon and radium concerned.