Radon Concentrations Measurement in Dwellings of Kufa Technical Institute, Iraq Using LR-115 Nuclear Track Detector

In this work, radon concentrations were measured in dwellings Kufa Technical institute, Iraq between November 2014 to February 2015 using time integrated passive radon dosimeters containing LR-115 Type II plastic track detectors. Also, we calculated the concentration of short-lived radon daughters, potential alpha energy, working level month, the annual effective dose rate, the annual equivalent dose rate and the excess lifetime cancer risk in all dwellings under study. The radon concentration in these dwelling ranges from (15.211 ± 2.745 to 32.445 ± 09.200) Bq/m3 with an average of (21.567 Bq/m3), which within the acceptable radon levels (50-150) Bq/m3 recommended by the International Commission on Radiological Protection (ICRP). The mean the excess lifetime cancer risk were found to be ranges from 35.458 to 75.633 with an average value of 50.297 per 106 persons. These values are within in the safe limits recommended by the international organizations.


Introduction
Radon is a unique natural element being found as a gas, noble, and radioactive in all of its isotopes. As gases, the isotopes are mobile and carry messages over significant distances, within the earth and in the atmosphere, but on the other side of the coin, inhalation can be a problem to one's health. The fact that radon is noble ensures that it is not immobilized by chemically reacting [1]. The decay of radon begins with uranium-238 and goes through four intermediate states to form radium-226, which has a half-life of 1,600 years. Radium-226 then decays to form radon-222 gas. Radon's half-life, 3.8 days, which provides sufficient time for it diffuse through soil and into homes, where it further disintegrates to produce the more radiologically active radon progeny ("radon daughters") [2].
The Health effects of radon, most notably lung cancer, have been investigated for several decades. Initially, investigations focused on underground miners exposed to high concentrations of radon in their occupational environment. However, in the early 1980s, several surveys of radon concentrations in homes and other buildings were carried out, and the results of these surveys, together with risk estimates based on the studies of mine workers, provided indirect evidence that radon may be an important cause of lung cancer in the general population. Recently, efforts to directly investigate the association between indoor radon and lung cancer have provided convincing evidence of increased lung cancer risk causally associated with radon, even at levels commonly found in buildings. Risk assessment for radon both in mines and in residential settings have provided clear insights into the health risks due to radon. Radon is now recognized as the second most important cause of lung cancer after smoking in the general population [2,3].
Since radon is constantly escaping from the ground, it is always present in the air, but under certain circumstances the concentration of radon in a building can be increased significantly over its normal outdoor level [4]. Most buildings have a confined air space with limited air movement and only a slow exchange with outside air. Consequently the concentration of any particulates or gases released into the building atmosphere will tend to increase above the concentration normally found in outside air. Radon can enter a building in a number of ways and once inside, the concentration of its particulate progeny will increase as the radon decays. Thus, high concentrations of radon gas in soils with high transport efficiency (i.e. loose, porous, dry soil) can lead to elevated radon concentrations in buildings [2,5].
Measurement of indoor radon is rather important because the radiation dose to human constitutes more than 60% of the total dose, including that from the natural sources [6]. Several techniques have been used to measure radon and are daughters concentration. LR-115 Nuclear Track Detector has been widely used for the measurement of time integrated radon levels in dwellings under different conditions [7][8][9][10][11][12].
The aim of the present work is to measure the indoor radon concentration and the annual effective dose in the Kufa technical Institute building of Kufa city by using SSNTDs technique LR-115 because there is no studying of radon concentration in this Institute.

Study area
Kufa city in Iraq, about 170 kilometres (110 mi) south of Baghdad, and 10 kilometres (6.2 mi) northeast of Najaf. It is located on the banks of the Euphrates River, with location of latitude (32°1'46"N), and longitude (44°23'53"E). It is located about 30 meters above the sea level, with a total area of nearly 28,824 km 2 and a population of nearly 110,000 [13].
Kufa city has a desert climate characterized by extreme heat during the day, an abrupt drop in temperature at night, and slight, erratic rainfall. The weather in kufa city is dry and hot in summer; cold and less rainy in winter. Temperature is moderate in winter at 18°C and 42°C in summer. Najaf does not have a seaport. Its lands are flat and leveled in areas linked to waters from the Euphrates River and higher in the southern portions of the desert areas, extending to the republic of Iraq [13,14]. The dwelling of Kufa Technical institute were built using different materials, such as cement, sand stones and bricks, iron structure, marble, and concrete. Several of these materials contribute significantly to indoor radon emission. We put tracks of LR-115 detector in living which has been measuring about 7 m x 4 m x 4 m, with one window and one door.
In this study we calculated the radon concentration for dwellings in Kufa Technical institute which are divided in to eight region as shown in Figure 1. Table 1 showed the sites of measurement in studied area for taking samples.

Methodology
Thirty one dosimeters, were prepared and distributed inside the underground levels of the dwellings in Kufa Technical institute. These locations are chosen to be representative of the whole region. Experimental methods for radon detection and measurements are based on alpha-counting of radon and its daughters. The plastic track detector (LR-115 type II) is a cellulose nitrate film of 12 µm thickness manufacture by Kodak Path, France. Due to its ruggedness and a fine window for recording alpha particles emanating from radon progeny, it is highly useful for integrated measurements from few days to several months [15]. These plastics films of size 1 cm x 1 cm were hung in the ceiling at distance 1 m above the earth of room. After the exposure period of 120 days, the detectors were etched for 120 minutes in 2.5 N NaOH solution maintained at 60°C. The etched detectors were washed with distilled water and finally dried in air and count the number of tracks by the track counting technique, which was performed using an optical microscope. The calibration factor for dosimeters exposed for range from (4-28) day to Radium 226 Ra (Radon source) of activity 3.3 kBq was calculated to be (0.0216 ± 0.0033) [(Bq.d. m -3 ) per (track.cm -2 )]. The value is approximately the same as that reported in many works [15][16][17].

Measurement of radon concentration
The tracks density is measured by using equation (1) [18]: Average number of total tracks Track density cm Radon concentrations (C Rn ) in present work are determined by the equation [19][20][21]: is calibration factor for dosimeters exposed (it gives

Calculation of EEC, PAE and WLM
The track density on the detector is related to the potential alpha energy (PAE) concentration expressed in Working Level (WL) units. WL is the concentration of any combination of radon progeny corresponds to 1.3 ×10 5 MeV of PAE per liter of air [22]. The resulting concentration of short-lived radon daughters expressed in term of an equilibrium-equivalent radon concentration (EEC), is related to the activity concentration of radon (C Rn ) by the equation (3) [22,23]: where F is an equilibrium factor which is equal 0.4 in indoor air [22,23].

Estimated the Excess Lifetime Cancer Risk (ELCR)
Indoor radon has been determined to be the second leading cause of lung cancer after tobacco smoking [24]. Radon effective dose value describes the harmful effects of radon on the human body; therefore, it is necessity to calculate the radon dose from radon concentration. There are large uncertainties in dosimetric assessments and epidemiological  aspects for the conversion of a radon exposure to a radon dose [25]. We used UNSCEAR's radon dose conversion factor as it lies between dosimetric and epidemiological dose conversions [26,27]. UNSCEAR suggests that in estimating the effective doses, the following factors are applied [28]: • An indoor radon decay product equilibrium factor of E f =0.4 • A radon effective dose coefficient factor of C f =9 nSv/(Bq h m −3 ) • An indoor occupancy factor of O f =0.8, which is the fraction time that people spend indoors, but not essentially in their homes. It means, during one year (T=365×24 h), people spend about 8,760 h at indoor spaces like home and office.
So, the equation for annual absorption dose (D Rn ) due to radon concentration is: where C Rn is the radon concentration in Bq/m 3 scale. By using this equation, annual radon effective dose has been calculated.
In the biological effect of radiation, to calculate the annual equivalent dose, two types of weighting factors are needed in order to estimate the level dose. A radiation weighting factor and a tissue weighting factor. The radiation weighting factor (W R ) for alpha particles is 20 as recommended by ICRP [29] and a tissue weighting factor (W T ) is applied. The weighting factor that used in this study is 0.12 [30,31]. The annual equivalent dose was then calculated using the following equation [

Results and Discussions
The minimum, maximum values and the average of radon 222 Rn gas concentrations for each monitored dwelling is reported in Table  2. The average radon concentration in dwellings was 21.567 Bq/m 3 , this variation in radon concentration is fundamental related with type of construction and age of the building, the minimum and maximum values for indoor radon concentration were found in sample (T10) and sample (T19) which equal to 15.211 ± 2.745 Bq/m 3 and 32.445 ± 09.200 Bq/m 3 respectively. The variable from one region to another due to different concentration of uranium in different regions, these results are within the radon levels (50-150) Bq/m 3 which are recommended by ICRP [34]. The values of equilibrium equivalent concentration (EEC), potential alpha energy (PAE) and monthly work level (MWL) of the study area are given in Table 3. The average values of equilibrium equivalent concentration, potential alpha energy concentration and monthly work level for each of the 31 samples were 8.630 Bq/m 3 , 2.332 mWL and 0.120 respectively. Table 4 shows the values of annual effective dose (D Rn ), annual equivalent dose (H E ) and the excess lifetime cancer risk per million persons per year (ELCR). The annual effective dose, the annual equivalent dose received by the residents of the study area varied from 0.383 mSv/y to 0.818 mSv/y with an average of 0.544 mSv/y and from 0.921 mSv/y to 1.964 mSv/y with an average of 1.306 mSv/y respectively. The high value of the annual effective dose in this study were (0.818) mSv/y. This value was lower than the permissible limits recommended by world health organization (WHO) [35] which it is equal (1-3) mSv/y. According to ours estimations, Table 4 shows the radon induced lung cancer risk for all dwelling in Kufa Technical institute was found and ranges from 35.458 to 75.633 with an average value of 50.297 per 10 6 persons. In general, these estimates indicated that the dwelling under study are characterized by low radon exposure dose, so the people who live in those dwelling are subject to relatively low risk factor for radon induced lung cancer. In general the low levels of radon concentration in these buildings can be attributed to the following reasons such as the good ventilation systems in most places and the good geometric designs, all walls are painted and most locations have covered floors and there are no cracks in the building basement. Table 5 summarizes the comparison between our results with those conducted in other countries. It seems that our results are near or around the other results [35][36][37][38][39][40][41][42][43][44].