Estimated concentration of Radon in Soil samples collected from Nasiriyah Governorate, Iraq, by using CR-39 detector

In this study, CR-39 detector was used to measure alpha particles emitted from radon gas in fifteen soil samples collected from Nasiriyah Governorate, Iraq. The results indicated that the concentration of radon gas varies from the highest concentration 122.40±19.11Bq m−3 in Bisan area and the lowest concentration of 69.71±17.90Bq m−3 in Hayyal - Muallimeen area, all values are less than the internationally recommended values 200-600 Bq m−3 mentioned by ICRP. Also, the calibration factor for the CR-39 detector was calculated and amounted to be 0.02 (tr.cm 2/Bq m −3 d).


Introduction
A polymer is a substance with a high molecular weight that is made up of a lengthy chain of repeating building blocks that all have the same structure.The components of the polymer can be natural or artificial [1,2].Due to their distinctive features, polymers now play a crucial and pervasive role in daily life.It is regarded as one of the fundamental components in a variety of industrial fields, including those that deal with plasticizer, rubber, Teflon, and other products [3,4].Solid nuclear track detectors (SSNTDs) a particular kind of polymer, are electrically insulating substances that may store the effects of ionizing radiation in them for a long time and manifest as dense fibrosis tracks [5,6].Due to their low cost, simplicity of use, accessibility, availability, durability, and effectiveness, the SSNTDs are widely used in plasticizers and highly regarded in many fields, including charged particle detection, geology, geophysics, neutron monitoring, space science, cosmic rays, nuclear physics, nuclear reactors, geology, and geophysics [7,8,9].Soil is main compound to grow the agriculture and it is important to humans and their health.It provides a resource that can be used as a shelter and for 1325 (2024) 012038 IOP Publishing doi:10.1088/1755-1315/1325/1/012038 2 food production.The main source for natural radioactivity is the terrestrial radionuclides.It has been found in every level of each region in the world that depends on the parent rocks which form the soil.The Natural of radioactive materials were represented the largest contribution of radiation doses received by human beings especially from radon gas and their daughter.Many studies in the world determined the level of natural radioactivity of 238 U, 232 Th and their decay products in soil.The survey indicated that the application of agricultural is one of the sources of radioactivity other than those of natural origin mainly due to the extensive use of fertilizers [10].The main goal of radiation protection is to understand radiation, provide the necessary information about it, and be aware of the variety of negative effects, it was necessary to find appropriate methods and tools to detect and measure radiation as well.This is due to the invisible nature of radiation.In addition to evaluating the need for these measurements and the suitable degree devices of the kind of measurement to reduce radiation doses, it may have adverse effects on people and the environment [11,12].Solid polymeric detectors are the best devices currently being used to detect ionizing radiation because they are simple electronic equipment to construct the nuclear track inside them [12,13].SSNTDs can monitor the concentration and spatial distribution of radioactive isotopes since they are unaffected by environmental influences, transparent, and sensitive to uncharged and charged particles (alpha and protons).When heavy charged particles are released, they either engage directly covalent polymer bonds, causing latent track damage.This is how nuclear track creation works strongly charged particles damage insulators in narrow tracks (~5-100A°) [6].The main objective of this study is to calculate the calibration factor for CR-39 detector and to measure alpha particles emitted from radon gas in soil samples collected from Nasiriyah Governorate, Iraq.

Study area
Fifteen samples were collected from selected areas of Al-Shatrah, Nasiriyah Governorate, Iraq, as source of radon gas and the soil samples chosen randomly based on previous studies in this area as shown in Table 1.The study area is located 350 kilometers south of Baghdad in the middle Euphrates region of southern Iraq.Al-Shatrah is one of the tributaries of Al-Gharraf River, which flows downward from Tigris River.It is part of Dhi-Qar (Nasiriyah) Governorate, which is located at 31° 14′ N, 46° 19′ E and has a population of around 2,040,126 as of the 2018 census [14].

Preparation Samples
Soil samples were brought to the laboratory for preparation, where the samples were dried, grinding, and then weighed (30 gm).The detectors were cut (1 cm × 1 cm) and cultured in tubes measuring 7.5 cm in length and 5 cm in diameter.The reagents were stored for 70 days with the samples and then taken out for etching where the CR-39 reagents were etched with 6.25 mol/L NaOH solution at 70 °C for 6 h.Finally, all detectors were washed with distilled water and dried, and then a micro-optical microscope with 400X magnification was used to measure the number of tracks [15,16,17].

Radon chamber design
The cubic chamber has been manufactured by the department of Physics, University of Al-Qadisiyah, Iraq.The dimensions are (20x20x20) cm 3 .Figure1 displays two images of the chamber.It is demonstrates the following describes, where the room content of hole are located at the top with 10 cm diameter, which used to put materials into the chamber.Type of solid-state detector was placed in the radon chamber of the organic detector CR-39 used with 500μm thickness (obtained from Pershore Moulding LTD Company, UK).The detectors were cut to size (1 cm x 1cm) and located inside the chamber.The chamber of PVC was considered as shown in Figure 1.A radium source (-226: 5i) was used to obtain radon.The calibration factor was calculated, as well as, radon concentration by using radon room designated for this purpose [18].
Figure1.The radon chamber to measure the calibration factor.

Calculation
The concentration of radon C Rn calculated according to equation 1 [14,15].Where ρ is the track density (tracks per millimeter squared), N t is the average number of tracks, A: the area of view field that can be seen through the microscope.In order to figure out the concentration of radon (Bq m -3 ) by used following equation 2 [15].
Where t is the number of days spent in storage (70) days, K (Track cm -2 per Bq m -3 .d),On the other hand, the annual effective dose mSv y -1 was measured by the equation 3 as follows [14].

Measuring the Calibration Factor (K)
CR-39 detector was calibration factor (K) is very important in detection.The K measured under the etching conditions was 6.25 mol L -1 of NaOH, and used the optimum time of etching 6 hours [12,13].
The results showed that longer periods of exposure to radon gas and a more uniform concentration of radon gas inside the chamber led to a higher track density as presented in Table 2. Using a source (Ra-226) to measure the radon concentration from equation 5, then by the equation 6 used to measure the calibration factor K value as following [14].
Where k is the calibration factor (. -2 per   -3 .),C Rn is the concentration of radon; ρ is the density of track (.-2 ); and t is the exposure time (d).

Results and Discussions
In this study, CR-39 detector was used to measure alpha particles emitted from radon gas of soil samples selected from Al-Shatrah, Nasiriyah Governorate, Iraq, listed in Table 3.The results indicated that the concentration of radon gas varies depending on the conditions of the samples, and this reason is attributed to the exposure of cities to military activities during wars.From Table 3, it is found that the average radon concentration is 95.32 ± 19.89.On the other hand, the annual effective dose AED and lung dose rate (D lung ) are shown in Table 3, it is found that the average AED mSv y -1 is 2.39.While the average D lung mSv y -1 was observed to be 3.8 mSv y -1 , and furthermore, the annual effective dose was within the recommended value 3-10 mSv y -1 ICRP.From the Figure 3, the comparing for the radon concentration and their risk, it is cleared the results have been below the acceptable level recommenced by UNSCEAR [10].The calibration factor of the CR-39 detector was also calculated and amounted to 0.02 (. - per Bq  -3 .) as presented in Table 2 [12,13].The CR-39 reagent was the most responsive to alpha particle sensitization, mainly because this reagent is an organic polymer containing bonds in the monomer of the reagent, and these bonds are relatively weak and break easily when exposed to radiation [18].

Conclusions
CR-39 polymeric detector was used to measure alpha-radon particles emitted from the soil sample which were collected from different location in Al-Shatra, Nasiriyah Governorate, Iraq.There was a difference in the concentrations of the areas from which samples were collected, this discrepancy is due to the difference in the exposure of some areas to military activities, the results obtained indicated a average concentration of radon measurements by CR-39 to be 95.32 ± 19.89 Bq m -3 , and showed that radon concentration in the study area less than the internationally recommended values 200-600 Bq m -3 UNSCEAR.The calibration factor for CR-39 detector was also calculated and amounted to 0.02 ( . - per Bq  -3 .).

Figure 2 .
Figure 2.The Calibration Factor (k) against the exposure time in the CR-39detector.

Figure 3 .
Figure 3.Comparison between averages of radon concentrations, D lung and annual effective dose AED.

Table 1 .
The samples sites collected from Nasiriyah governorate, Iraq.

Table 3 .
The activity concentrations of natural radioactivity in soil samples collected from