Measurements of radon , thoron and their progeny concentrations using twin cup dosimeter for indoor Al-Madaan city – Baghdad – Iraq

In this study, the activity concentrations of indoor radon, thoronand their progeny have been measured in air for 61 differentlocations of Al-Maddan city using twin cup dosimeter. Furthermore,some useful parameters concerning the health hazards have beenestimated; working level month (WLM), annual effective dose (Eff),and excess lung cancer per million person per year (ELC).The resultsshow that the values of radon gas levels in the investigated districtsvaried from 56.28 to 194.43Bq/m3with an overall average value132.96Bq/m3, while 0.313 to 1.085 for WLM with an overall average0.740, respectively. The value of Eff and ELC have been found tovary from 1.420 to 4.918 mSv/y with an overall average value3.354mSv/y, and 852 to 2951 with an overall average value 2013,respectively. For thoron gas only, the results showed that the thoronactivity concentration varied from 15.05 to 172.40 Bq/m3 with anoverall average 76.48 Bq/m3, and 0.021to 0.240for WLM with anoverall average 0.106, respectively. The values of Eff and ELC havebeen found to vary from 0.256 to 2.94 mSv/y with an overallaverage1.30 mSv/y and from 57 to 652 with an overall average of298, respectively. The concentration of radon progeny varied from59.44 to 301.39 Bq/m3 with an overall average 157.62 Bq/m3. Theresults illustrated that there is a large variation in the values of themeasured concentrations. This is due to the wide variation in theconstruction of the houses in Al-Madaan city. However, allinvestigated locations have radon concentration below the actionlevel (200-300Bq/m3) that recommended byICRP. Therefore, there isno health hazard of radon in the region of Al-Madaan city wheremeasurements have been performed.


Introduction
Radon is ubiquitous gas present in the natural environment supposed to be the most important factor of health hazards caused by natural radioactivity.Inhalation of radon and its progeny can cause a significant health hazard, if it is present at enhanced levels beyond maximum permissible limit [1,2].There are various factors, which affect radon levels such as the difference in soil texture or porosity.The exact source of radon in soil air may be at a deep distant from the surface of the ground.The lower radon concentration in the top layer of the soil is attributable to the proximity of the soil to the atmosphere [3].The radiation dose received by a dweller from all natural sources, about 52% is only due to breathing of radon and its short-lived daughter products [4].It is well documented fact that the pathological effects like respiratory functional changes and the occurrence of lung cancer may be caused by the long exposure of a person to the high radon levels [5][6][7][8].The measurements of radon can be continuous or discrete by carrying out grab sampling.It can be passive or active.
Several techniques are used for the measurements of radon, thoron and their progeny.Some techniques measure the short-term values are called active techniques and other measuring the integrated values is called passive techniques.For the direct measurements of radon, thoron and their progeny, LR-115 type-II plastic track detectors are placed in a container or double dosimeter cup.This simple cup was made of cardboard in different versions [3,9].The α-particles from radon and its progeny have a range of about 5 cm in air.The measurement of radon concentration is a simple event.Both radon isotopes ( 222 Rn and 220 Rn) would be theoretically detected unless some sort of discriminating mechanism applied [10].There are generally two ways to solve the problem; the first is that preventing the thoron entering the detecting device, and another is to discrimination between radon and thoron isotopes.
The Twin cup technique using LR-115 detectors [11] have been employed to measure the concentration of radon and its progeny in the indoor environment for the assessment of detrimental effects among the human population living in the study areas of districts of Al-Madaan city, which is a large city in Baghdad (the capital of Iraq).
and are the track densities (in tracks.cm - ) in membrane mode and in filter mode, respectively.and are the radon and thoron concentrations (in Bq.m -3 ).
The detector 3 exposed externally (i.e., 'bare mode' exposure) registers the tracks of radon, thoron and their αemitting progenies present in the ambient air.The cup detector sensitivity for radon is close to that of the bare detector.The track density for 'bare exposure is , and calibration factor (in tracks.cm - .d -1 /Bq.m -3 )should be same for all αemitters [13].
However, another parameters concern radon and thoron concentrations can be estimated.These parameters are; the working level month, the excess lung cancer per million persons per year (ELC), and the annual effective dose (Eff), which can be explained as follow: The working level (WL) is based on the assumption that 100 pCi (=3.7 Bq) worth of 222 Rn is present a liter of air and that each of its four short-lived daughters is also decaying is secular equilibrium with it (i.e. they all display an activity of 3.7 Bq each).The relation between the units, WL, Bq/L and Bq/m 3 is [7]: 1 WL = 3.7 Bq/L = 3.7 * 10 3 Bq/m 3 .Therefore, WLM defined as WL for 170 hours (per month) [7].Lung cancer risk is defined as the excess deaths per million persons per year (MPY) due to lung cancer per unit exposure to radon and its short lived daughters.A risk coefficient, defined as the number of lung cancer cases per MPY per WLM, is determined from the epidemiological data of the occupationally exposed mine workers.The excess lung cancer risk (ECL) per MPY was estimated by the following equation [7]: Excess Cancer Risk = F * Risk factor * O * WLM (4) The UNSCEAR committee suggests the equilibrium factor (F) 0.4 for radon and 0.1 for thoron and occupancy factor (O) 0.8 for the indoor environment [6].From the measured indoor radon (or/and thoron) concentrations, the annual effective dose due to inhalation of radon gas (Eff) have been calculated using the UNSCEAR model [23]: Eff (mSv/y) = CRn * F * O * T * D (5) where T is time in hours per year (8760 h/y) and D is the dose conversion factor (9.0 × 10 -6 mSv / Bq m -3 h).

Results and discussion
Table 1 shows the investigated locations of the study area, radon, thoron, and their progeny concentrations.
The radon concentration varied from 56.28 to 194.43 Bq /m 3 with an overall average value of 132.96Bq/m 3 , the thoron concentration varied from 15.05 to 172.40 Bq/m 3 with an overall average of 76.48 Bq/m 3 , and their progeny concentration varied from 59.44 to 301.39 Bq.m -3 with an overall average of 157.62 Bq/m 3 .Furthermore, the lowest value of radon concentration was observed in Al-Rasheed district, which can be classified as residential area that does not include any agricultural soils lands and this district, in general, have a new buildings, i.e. the buildings of this district don't have cracks.The highest was observed in Aalioi Al-Shlal Village1, which includes many agricultural lands.It is known that the agricultural lands contain soils with high amounts of fertilizer that compose with a significant concentration of 238 U.However, it is clear that there is a large variation in the values of the measured concentrations.This can be attributed to the wide variation in the construction of the houses in Al-Madaan city.There are houses made of clay bricks and plastered without any white-wash having higher radon levels.The lower values of radon and its progeny have been observed in the houses which were plastered and painted with good quality distemper and adequately ventilated.However, all the values of the radon concentration below the allowed permissible limit, 200-300Bq/m 3 , recommended by ICRP [22].Furthermore, Fig. 4 illustrates the ratios between the radon to the thoron concentrations.This figure suggested that the average ratio between radon concentration and the concentration of thoron gas is 2.99 which is below the normal ratio which is four indicating that the study area has soils contain higher concentrations of thorium-232 (which results the thoron gas).Furthermore, one can easily note the variation of the ratio with the investigated districts and increasing it in some districts (i.e.increasing U-238 against Th-232).These increasing ratios could be attributed to the nature of soils, which are agricultural origin that include fertilizer contains significant concentrations of uranium-238.

LM) and an ar (ELC). LM) and an ar (ELC).
ation in houses in d that the re don, thoron ooqi oron cted, with , but uced are uced ation going atical on or uring even asily nnual nnual the Alsults n and their progeny were higher in 'bare mode' exposure than by the twin cup dosimetric analysis.In addition, the results suggested that the soils of the study area have thorium nature because the overall average value of the ratio between radon and thoron concentrations deviated to thoron.Also, the estimated results of Eff showed that the main contribution of the total annual absorbed dose comes from the radon inhaled effective dose.However, all investigated locations have radon concentration below the action level (200-300 Bq.m -3 ) recommended by ICRP [22].Therefore, there is no health hazard of radon in the region of Al-Madaan city where measurements have been performed.

s of Al-Mada
aan city.