Detecting the Possibility of Soil Pollution with Radon Emissions for an Area Located within Baghdad University Campus- AL-Jadiriyah

This research deals with the detection of possible surface soil pollution by radon emissions for an area located inside the university of Baghdad campus at ALJadiriyah / Baghdad. The area is about 5625 m 2 and located near the College of Science for Women. The area used as construction rubbles dump yard in the past, while recently it is covered with Silty Clayey soil furnished with grass and used as a playground. A surface survey performed on October 2018 by gridding the area into 36 stations where surface radiometric pollution readings recorded and soil samples collected by using an auger for the top 30 Cm which represents the root zone of the area. Soil samples tested in the laboratory by using can technique with CR-39 type track detectors, while surface readings performed by using a portable Geiger counter device. Soil surface readings and laboratory analysis results were processed by computer in order to draw contour maps which showed the variation of radon emission anomalies across the area. The aim behind this processing and interpretation is to provide an evaluation for the health environmental impact related to the radioactivity of the top soil and the area surface. The results of this study showed that radon emissions were below the standard limits and this makes it possible to invest the area for future human housing and other activities.


Introduction
Radon 222 is one of the periodic table elements located within the range noble elements (Noble gases) (helium-neon-xenon, etc.), the gas is invisible and tasteless and odorless, this component is generated within the intermediate stage of decomposition for uranium-238 which includes the produce of radon generating several other radioactive elements, the series decays for this element ends by producing lead [1], where α is the gross alpha: Radon is one of the inert gases which has an atomic number 86, while it is mass number of his most stable state is 222 with a density of 9.7 kg.m -3 and boiling point of -61.8 C o , its degree of freezing is about -71 C o [2]. This gas is heavier than air seven times but generally, it is about one and a half and it exists in all the places at all the times [3].
The Ra 222 natural nuclear radiation is mainly generated by the natural decay of a series of uranium sources 238 U, thorium 232 Th and uranium 235 U which considered the only metal that exists in the gaseous state [4]. Radon has three radioactive isotopes which are radon 222 Rn, thoron 220 Rn, and actinon 219 Rn. The counterpart which is usually taken in consideration in most geological and environmental studies is the 222 Rn due to its relatively long half-life (3.82 days), while the effects of other isotopes 220 Rn and 219 Rn are neglected because they possess shortest half-life (5.66 and 3.92 second), respectively [4]. The US Environmental Protection Agency EPA has proposed the maximum concentration of radon in drinking water is 1100 Bq/m 3 [5].
The radon leads to health risks via two paths, first is the inhalation of radon and its decay products after liberation from water to the air of houses, and second is the direct ingestion of radon in drinking water. The inhalation of radon decay products increases the risk of lung cancer, the radon gas was not linked to other more types of cancer and the risk of inhalation may exceed that of ingestion [6].
The fact is that alpha particles are usually emitted during radon decay, it represents a heavy charged particles which occur by colliding atoms. This type of radiation is able to produce a defect to the tissues of organs and body cells in addition to the large disturbances which are mainly chemical effects at the molecular level. The average length of the path of alpha particles in soft tissue is about 40µm. The capacity of ionizing increases to more than 1000 times when it is caused by beta particles energy, therefore it could be more destructive to human tissues as compared with the exposure to radon decay products [7,8]. The annual effective equivalent dose for humans according to the WHO was estimated up to 2mSv.y -1 , while radioactive background unusual environment for human inhalation of 222 Rn is at a rate of 0.8 mSv. y -1 [9].
The Study is area located inside the university of Baghdad Scientific complex at AL-Jadiriyah / Baghdad as it shown in the Figure1. Recently, the area is rehabilitated and furnished with siltyclayey soil then planted with grass. The origin of the area and surroundings is the sediments of Tigris River which are mostly alluvium deposits.
This study aims to detect any radon gas radioactivity in the area which may produce environmental impact during the present and future investment for this area.

Materials and Method
The surface top soil surveying was achieved on October 2018 by using a portable Geiger counter device, Figure-   Iraqi Journal of Science, 2019, Vol.60, No.9, pp: 1985-19961988 Can technique with CR-39 type track detectors , 200μm thickness and dimensions of 1cm×1cm was used in the present study. Dosimeters, was shown in Figure-4, after an exposure time of 30 days, the dosimeters were collected and chemically etched (6.25N NaOH at 70 C o over 4 hour period) [10]. To account the number of tracks per cm 2 occurred in each detector an optical microscope with a magnification of 40X was used with CCD camera (   The CR-39 detectors exposed to the samples which are affected by radon and its daughters in the volume of air around them. In relating the observed track densities to the radon and its daughter activities per unit volume of air, the following equation has been used [11]. (1) where ρ, is the number of tracks per cm 3 .
x, is a constant with dimension of length (cm). A, is the alpha activity per unit volume (disintegrations per unit time per cm 3 ).
The value of the constant x is the sum of separate constants calculated for all isotopes ( 222 Rn, 218 Po and 214 Po). In order to estimate the radon concentration, experimental method for radon detection and measurement are based on alpha-counting of radon and its daughters. The track density was calculated in terms of number of tracks per mm 2 , and then the average number of tracks was determined by processing an unexposed films CR-39 detector under identical etching condition. The signal measured by etched track detectors is integrated track density, ρ (track. mm -2 ) recorded on the detector, K i the average value of the calibration factor of 222 Rn in (Bq. day m -3 ) per (tracks. mm -2 ) and T exposure time (day) has been applied to determine the activity of 222 Rn concentration (C Rn ) in Bq/m 3 by using the following Equation [12]: Where: Ki, is the calibration factor with the dimension of length or equivalent to (tracks.m -2 .d -1 per Bq.m -3 ) and ρ is the Track Density.
Usually, all measurements of radon levels in the home or outdoors are expressed as the concentration of radon in units of picocuries per liter of air (pCi/liter), or in SI units as Becquerel per cubic meter (Bq/m 3 ). The radon daughters are expressed in Working Levels (WL), which is given by [13]: Where: F is the equilibrium factor and recommended as FC Rn = 0.4 [14].
Furthermore, Qureshi. [15], proposed a method to calculate the annual effective dose of Working Level Month (WLM) units, which is given by: Therefore, the relation between the effective dose and Radon concentration is given by: E ff = G C Rn (5) Where: G is a constant (conversion factor).
In this study measurement of indoor radon concentration (C Rn ), potential alpha energy concentration (PAEC) and annual effective dose (HE) have been performed. The potential alpha energy concentration (WL) was calculated using Eq. (3), annual effective dose equivalent (WLM/year) and effective dose also have been calculated using Eqs.(4) and (5) respectively. Radon exhalation rate was also calculated using the following equation [11]: Where: E x is radon exhalation rate (mBq/m 2 .h), C t is mean radon concentration as measured by CR-39 detector (Bq/m 3 ), V is volume of the can (m 3 ), t is the exposure time, λ is the radon decay constant and S is the surface area from which radon is exhaled into the closed can.

Results and discussion
The overall results for radon concentrations in Bq⁄m 3 , radon exhalation rates in Bq⁄m 2 .h, the equilibrium equivalent 222 Rn concentration (CEEC in Bq⁄m 3 ), and the Annual Effective Dose Eff (in mSv/y) for thirty six soil samples were given in the Table 1. Radon concentrations were measured by making dosimeter from closed can technique, as shown in Figure-1, which means that the air at the whole exposure time was confined within the container. The overall average value of the radon concentrations of 222 Rn for soil samples was 1832.      A linear positive relationships appeared as shown by the Figures-(9,10) with a maximum correlation coefficient (R=1).
The grid nodes data for the surveyed stations were input to computer software in order to construct contour maps by adopting the kriging interpolation method [16]. Contour maps were constructed to display the variation of the measured and calculated parameters across the study area as shown in the Figures-(11, 12 and13).  The sections across the A-A \ profile lines show maximum anomaly at the scale distance of 50m which gives a primary indication for the source of maximum contaminated area with radon emissions.

Conclusions
The radon concentration values obtained were varied within the soil samples of the current studied area. The recorded values of radon concentration were lower than the standard limits. A linear relationship has been traced between the annual effective dose and the measured radon concentrations. The overall average value of the radon concentrations of 222 Rn for soil samples was 1832.7 Bq⁄m 3 . The maximum concentration of 222 Rn appeared in station No. 33 and the minimum concentration appeared in station No. 4 as shown in Figure-