Radiation Protection Dosimetry Advance Access published April 7, 2014 Radiation Protection Dosimetry (2014), pp. 1–6
doi:10.1093/rpd/ncu058
EXPOSURE TO INDOOR RADON AND NATURAL GAMMA RADIATION IN SOME WORKPLACES AT ALGIERS, ALGERIA M. Aı¨t Ziane1,*, Z. Lounis-Mokrani1 and M. Allab2 1 Laboratoire de Dosime´trie des Rayonnements Ionisants, Centre de Recherche Nucle´aire d’Alger (CRNA), Algiers, Algeria 2 Laboratoire SNIRM, Universite´ des Sciences et de la Technologie Houari Boumediene (USTHB), Algiers, Algeria
Radon activity concentrations have been measured in 34 workplaces throughout Algiers nuclear research centre, in Algeria, during some periods between March 2007 and June 2013 using Electret ion chambers, nuclear tracks detectors and an AlphaGuard system. The indoor radon levels range from 2 to 628 Bq m23 with an average indoor concentration equals to 92 Bq m23, whereas the estimated outdoor radon concentrations range from 2 to 14 Bq m23 with an average value of 6 Bq m23. This study also focused on parameters affecting radon concentration levels such as floor number, ventilation and atmospheric parameters. Furthermore, the mean gamma rates have been measured in the different investigated locations and have been found to be varying between 33 and 3300 nSv h21. The annual effective dose for workers calculated using the appropriate equilibrium and occupancy factors is lower than the value recommended by International Commission on Radiological Protection in its Publication 103.
INTRODUCTION Dosimetry laboratory of CRNA has undertaken an extensive investigation this last decade in order to evaluate the indoor radon concentration in some dwellings and workplaces with the aim of establishing a radon national reference level. In fact, indoor radon in workplaces is an important existing exposure situation, which needs specific recommendations as pointed out by the International Commission on Radiological Protection (ICRP) in its Publication 65(1). In its report 103 published in 2007(2), the commission recommends also that national authorities should set national reference levels as an aid to optimisation of protection against radon exposures with account taken of the prevailing social and economic circumstances. The reference level for 222Rn should be set at a value that does not exceed an annual average activity concentration of 222Rn of 1000 Bq m23(2, 3). This work has been undertaken to determine the annual-averaged radon concentration in several workplaces in nuclear research centre. MATERIALS AND METHODS The selected workplaces include rooms hosting different activities located in the basement and at different floors of the buildings built with different types of materials. Sampling More than 140 radon measurements were performed in 34 different locations in Algiers nuclear research
centre (Table 1), during a large climatic cycle between March 2010 and June 2013, adding to some scarce measurements performed in 2007(4). This Centre is located at 368460 4700 N and 3830 700 E at an altitude of 108–120 m above the sea level. The geology of the region is formed by sedimentary rocks, basically clay, marls and sandstone. The ambient climate is Mediterranean with cold wet winters (mean December temperature 5–118C, precipitation 126 mm) and hot dry summers (mean May temperature 23–308C, precipitation 7 mm). Experimental procedures Electret ion chambers (EIC), nuclear tracks detectors (NTD) and an AlphaGUARD (AG) continuous radon device were used for the measurements of the radon concentrations: † EICs consisting of ‘S’ chambers equipped with short-term electrets were deployed for 7 d during hot (May–July) and cold (November–January) periods and ‘L’ chambers loaded with long-term electrets were exposed for 6 months during cold (September– February) and hot seasons (March–August). † NTD with LR-115 type II SSNTD film (KODAK, France) in a closed can were exposed for 6 months and then chemically etched in 2.5-M NaOH at 608C for 90 min and counted automatically with a spark counter(5). † Continuous radon monitor (AlphaGUARD PQ2000 PRO) was used continuously every 10 min during 30 h. Air, temperature, barometric pressure and humidity were simultaneously registered.
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M. AIT ZIANE ET AL. Table 1. Average radon concentrations in different workplaces and status of the ventilation system, level, exposure situation, building materials and measurement technique. Location
BM
V
Exp
MT
Rn (Bq m23)
0 0 0 0 0 21 0 1 4 0 2 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 0 1
C S S C C C C C C C C C C S S S S CB CB CB CB CB CB CB CB CB CB CB CB CB CB CB CB C
2 2 2 þ þ þ þ þ þ 2 2 þ 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 þ
E E E E E E E E E E E E E P P P E E E E P E E E E E E E E E E E E E
1,2,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,4 4 4 3 1,3,4 1,4 1,2,3,4 3 4 3,4 1,3,4 1,3 4 3 3 1,2,3 3,4 4 1,4 1,4
191 14 14 341 25 63 181 29 5 37 23 10 4 244 602 628 76 13 68 76 240 37 33 14 14 20 25 2 6 7 25 12 36 29
ERn ¼ ðC Rnin Fin Hin þC Rn out Fout Hout ÞtG
ð1Þ
Eg ¼ ðDin Hin þDout Hout ÞtK
ð2Þ
where the subscripts ‘in’ and ‘out’ refer, respectively, to indoor and outdoor locations. CRn (Bq m23) is the average radon concentrations, F is the equilibrium factor (Fin ¼ 0.4, Fout ¼ 0.6)(3, 7) and G is the dose conversion factor (9.0 nSv h21 Bq m23)(7). D (nGy h21) is the measured gamma dose rate, K is the dose coefficient relating to adults equal to 0.7 Sv Gy21(7) and H is the occupancy factor(3) determined assuming 40 working hours week21, throughout the 48 working weeks of the year. Assuming that the workers spent generally 8 h d21 in their working place, the occupancy factor is set equal to 0.22 for Hin and 0.20 for Hout. The time t is in hours for a year (8760 h y21). RESULTS AND DISCUSSION
Level (L): under ground floor: 21, ground floor: 0, first floor: 1, second floor: 2, fourth floor: 4 BM, building materials: C, concrete; CB, clay brick; S, shack. V, ventilation system with (þ), without (2). Exp, exposure situation: E, existing; P, planned. MT, measurement technique: ST-EIC: 1, LT-EIC: 2, AG: 3, NTD: 4.
Gamma dose rates were measured in the examined locations and around the buildings for 8 h using a High-Pressure Ionization Chamber RS-112 at a height of 1 m above the ground and at a distance of 50 m from the outer walls for the outdoor estimation(6). Dose calculations The annual mean effective dose ERn (mSv) due to the radon and its progeny expected to be received by workers staying in the selected locations and the
In all workplaces, pairs of ST and LT type electrets were installed simultaneously to estimate the reproducibility in radon determination. Duplicate measurements were highly correlated and a Students0 t-test for paired samples showed no statistically significant difference ( p ¼ 0.531 and p ¼ 0.524) between results obtained by the two detectors for both types of electrets, respectively. A variation of ,5 % on the average was deduced as previously noticed by Papachristodoulou et al.(8). These measurements are also in good agreement with the corresponding sets of continuous AG measurements, as shown in Figure 1. In this figure, 1-week radon measurements using ST-EIC and the corresponding AG ones averaged in hourly intervals were reported. The observed relationship is linear with a slope equal to 1.0129, and a correlation coefficient R 2 of 0.9981, the results comparable with those given by Denman et al.(9) (slope: 1.0693; R 2: 0.9615). Arithmetic (AM) and geometric (GM) mean radon concentrations and ambient gamma dose rates in outdoor and indoor air averaged over all locations are given in Table 2. Their corresponding annual effective doses, evaluated by using Equations (1) and (2), respectively, are also reported in this table. Radon concentrations and effective doses Indoor radon concentrations in the investigated locations range between 2 and 628 Bq m23, with an AM of 92 Bq m23, while the outdoor radon concentrations vary between 2 and 14 Bq m3, with an AM of 6 Bq m23 (Table 2). Highest radon concentrations were recorded in planned exposure workplaces
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 3 34
L
annual effective dose originating from the gamma radiation source Eg (mSv) are estimated according to the UNSCEAR model(7):
EXPOSURE TO RADON AND GAMMA AT WORKPLACES
Figure.2. Distribution of radon concentration measured in the investigated workplaces.
Table 2. Ambient gamma dose rate and radon concentration in outdoor and indoor air and estimated annual effective doses. Gamma dose rate (nGy h21)
Outdoors Cosmic Terrestrial Total Indoors Cosmic Terrestrial Total
AM+SD
GM
Range
31.2 142.8 + 17.0 174.0 + 17.0
31.2 141.8 173.2
108.8–168.8 140.0–200.0
31.4 + 0.2 282.9 + 792.0 307.9 + 792.1
31.4 128.6 160.2
31.1 –31.6 27.9 –4689.3 52.9 –4714.3
Radon concentration (Bq m23) AM + SD
GM
Range Figure 3. Radon concentration at different levels.
Outdoors Indoors
6+4 92 + 156
5 34
2 –14 2 –628
Gamma effective dose (mSv y21) AM + SD Outdoors Cosmic Terrestrial Total Indoors Cosmic Terrestrial Total
GM
Range
0.04 0.19 + 0.02 0.23 + 0.02
0.04 0.19 0.23
0.15 –0.23 0.19 –0.27
0.04 + 0.00 0.38 + 1.07 0.42 + 1.07
0.04 0.17 0.22
0.04 0.04 –6.33 0.07 –6.36
Radon effective dose (mSv y21) AM + SD Outdoors Indoors
0.04 + 0.02 0.64 + 1.08
GM 0.03 0.23
Range 0.01 –0.09 0.02 –4.35
such as the crushing and grinding units and the ore storage room. Except the latter locations, all values are ,200 Bq m23, in line with the recommendations of the ICRP and the International Atomic Energy Agency (IAEA)(2, 3). The radon concentrations in studied workplaces are given in Figure 2. The hypothesis that values are log–normally(10) distributed is accepted using the Shapiro-Wilk test over all distribution of radon concentrations (x2 ¼ 0.5664, R2 ¼ 0.9916). A general trend of decreasing radon concentration is observed from the basement towards upper floors except for buildings where the radon is due to elevated radium in the construction materials (Figure 3). Therefore, the authors’ future radon measurements will be carried out only on the lowest floor in any building. The high concentrations observed in some workplaces generally located in the basement and due to exceptionally large influxes of radon (building materials, bedrocks, etc.) can be strongly lowered by using ventilation devices.
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Figure 1. Correlation of ST-EIC with AG monitor radon measurements.
M. AIT ZIANE ET AL. Table 3. Ventilation effect. Radon concentration (Bq m23) Location
Ventilation (2)
Ventilation (þ)
A B C
1124 + 319 156 + 52.71 183.7 + 48.72
33.02 + 1.20 63.28 + 20.91 49.06 + 16.09
Figure 4. Mean seasonal radon concentrations.
Results of radon measurements in three such workplaces, performed with and without a ventilation system, are reported in Table 3, with (þ) and (2) notations, respectively. The mean seasonal indoor radon concentration has been estimated including all the investigated locations. It can be noted that the average radon in the winter is higher than in the other seasons because of the closed atmosphere in the buildings during the cold season. Average radon concentrations are lowest in summer, while the average radon concentration in autumn is close to that in spring (Figure 4). The average indoor radon concentration dependence on meteorological parameters including ambient temperature, atmospheric pressure and ambient relative humidity, the values of which were averaged over the sampling periods have been observed and no correlation was found between each of these physical parameters and the radon concentrations. However, the indoor radon concentrations indicate a weak positive correlation (R2 ¼ 0.5527) with the gamma dose rates in the air (Figure 5) due to terrestrial gamma radiation as already observed in the previous paper(11). A more acute observation of the variation of the diurnal indoor radon concentration versus the atmospheric parameters reveals that radon fluxes are in fact somehow positively correlated with the atmospheric pressure and negatively correlated with the relative humidity as shown in Figure 6, which reports the
results obtained in the same workplace during 3 d in August. This result has already been suggested by Rowe et al.(12). However, no correlation has been observed between radon concentrations and temperature or ambient gamma. As a whole, indoor radon concentration measurements are low to moderate in the investigated locations and are below the 1000 Bq m23 reference level recommended by ICRP(2, 3). The average of annual indoor radon concentration in the CRN is 34 Bq m23. The annual effective doses, ERn, obtained by applying Equation (1) are reported in Table 2. The effective dose due to indoor radon varies from 0.02 to 4.35 mSv y21 with a GM value of 0.23 mSv y21. These dose values are also lower than the effective dose values between 3 and 10 mSv y21, given as the range of action levels recommended by the ICRP(2). Gamma dose rates and effective doses Dt indoor and outdoor dose rates (Dt,in and Dt,out, respectively) due to terrestrial gamma radiation have been evaluated from total dose rate measurements D (Din and Dout, respectively) and the cosmic component , following the expression(13): Dt ¼ D ðS Dc;out Þ
ð3Þ
where S the building shielding factor assumed to account for the reduction of cosmic dose rate indoors is equal to 0.8 indoors and 1 outdoor(7). Dc,out is equal to 31.2 nGy h21 in the investigated area, as estimated using Bouville and Lowder formalism(8). The results, displayed in Table 2, show a much higher indoor terrestrial component compared with the outdoor one with a ratio equal to 1.98 (in the range of 0.6 to 23(7)) probably because of the effects of building materials and the existence of planned radon
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Figure 5. Variation in radon concentrations with ambient gamma dose rates.
EXPOSURE TO RADON AND GAMMA AT WORKPLACES
exposure workplaces. Furthermore, the indoor effective doses due to ambient gamma deduced from Equation (2) vary from 0.07 to 6.36 mSv y21 with a GM value of 0.22 mSv y21 even when including the planned exposure workplaces investigated in this work. This value is in the range of 0.3–1.0 mSv y21 established by UNSCEAR from worldwide results(13). CONCLUSION In this study, a good agreement is observed between the values obtained with both detector types suggesting that the more convenient EIC system can be valuably used in the radon campaign with a view to estimate the national radon reference level. The
maximum average radon concentration is equal to 628 Bq m23, while in most workplaces, the average indoor radon concentrations are below the 200 Bq m23 upper limit. Higher concentrations have been observed in workplaces at lower floors in the building except in the workplaces with planned radon exposure. The building materials and bedrock are some of the sources of radon inducing high radon concentrations in a working enclosure which can be strongly reduced by artificial ventilation system. The radon concentration distribution can be well described by a log–normal distribution. This pilot study will be extended to different locations over the country in order to determine the national reference level of radon exposition in workplaces.
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Figure 6. Variation in radon concentrations as a function of time compared with averages of humidity (rh), temperatures (T), atmospheric pressure (P) and ambient gamma.
M. AIT ZIANE ET AL.
REFERENCES 8.
9.
10. 11.
12. 13.
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1. ICRP. Protection against radon-222 at home and at work. ICRP Publication 65. Ann. ICRP 23(2). Pergamon Press (1993). 2. ICRP. The 2007 recommendations of the International Commission on Radiological Protection. Publication 103. Pergamon Press (2007). 3. IAEA Safety Standards Radiation for protecting people and the environment. Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards Interim edition No. GSR Part 3 (Interim), (Vienna: IAEA) (2011). 4. Aı¨t Ziane, et al. Radon and environmental gamma assessment in some workplaces at Nuclear Research Centre of Algiers. ICNTS (2008). 5. Cross, W. G. and Tommasino, L. A rapid reading technique for nuclear particle damage tracks in thin foils. Radiat. Effects 5, 85–89 (1970). 6. Gorja´na´cz, Z., Va´rhegyi, A., Kova´cs, T. and Somlai, J. Population dose in the vicinity of closed Hungarian uranium mine. Radiat. Prot. Dosim. 118(4), 448–452 (2006). 7. UNSCEAR. Report to the General Assembly with Annexes, New York, Vol. I: Sources, Annex B: Exposures
from natural radiation sources: 83– 156. United Nations, New York (2000). Papachristodoulou, C. A, Patiris, D. L. and Ioannides, K. G. Exposure to indoor radon and natural gamma radiation in public workplaces in north-western Greece. Radiat. Meas. 45, 865–871 (2010). Denman, A. R, Groves-Kirkby, C. J, Phillips, P. S, Crockett, R. G, Woolridge, A. and Gillmore, G. K. The practical use of electrets in a public health radon remediation campaign. J. Environ. Radioact. 84(3), 375–391 (2005). Bossew, P. Radon: exploring the log-normal mystery. J. Environ. Radioact. 101, 826– 834 (2010). Bajwa, B. S, Singh, H, Singh, J, Singh, S. and Walia, V. A combination study of indoor radon and gamma radiation levels in Tusham ring complex. Radiat. Meas. 43, S475–S478 (2008). Rowe, J. E, Kelly, M. and Price, L. E. Weather system scale variation in radon-222 concentration of indoor air. Sci. Total Environ. 284, 157–166 (2002). UNSCEAR. Sources and effects of ionizing radiation. UNSCEAR Report to the General Assembly with Scientific Annexes, Vol. 1, Annex B—Exposures of the public and workers from various sources of radiation: 229– 236. United Nations (2008).
doi:10.1093/rpd/ncu058
EXPOSURE TO INDOOR RADON AND NATURAL GAMMA RADIATION IN SOME WORKPLACES AT ALGIERS, ALGERIA M. Aı¨t Ziane1,*, Z. Lounis-Mokrani1 and M. Allab2 1 Laboratoire de Dosime´trie des Rayonnements Ionisants, Centre de Recherche Nucle´aire d’Alger (CRNA), Algiers, Algeria 2 Laboratoire SNIRM, Universite´ des Sciences et de la Technologie Houari Boumediene (USTHB), Algiers, Algeria
Radon activity concentrations have been measured in 34 workplaces throughout Algiers nuclear research centre, in Algeria, during some periods between March 2007 and June 2013 using Electret ion chambers, nuclear tracks detectors and an AlphaGuard system. The indoor radon levels range from 2 to 628 Bq m23 with an average indoor concentration equals to 92 Bq m23, whereas the estimated outdoor radon concentrations range from 2 to 14 Bq m23 with an average value of 6 Bq m23. This study also focused on parameters affecting radon concentration levels such as floor number, ventilation and atmospheric parameters. Furthermore, the mean gamma rates have been measured in the different investigated locations and have been found to be varying between 33 and 3300 nSv h21. The annual effective dose for workers calculated using the appropriate equilibrium and occupancy factors is lower than the value recommended by International Commission on Radiological Protection in its Publication 103.
INTRODUCTION Dosimetry laboratory of CRNA has undertaken an extensive investigation this last decade in order to evaluate the indoor radon concentration in some dwellings and workplaces with the aim of establishing a radon national reference level. In fact, indoor radon in workplaces is an important existing exposure situation, which needs specific recommendations as pointed out by the International Commission on Radiological Protection (ICRP) in its Publication 65(1). In its report 103 published in 2007(2), the commission recommends also that national authorities should set national reference levels as an aid to optimisation of protection against radon exposures with account taken of the prevailing social and economic circumstances. The reference level for 222Rn should be set at a value that does not exceed an annual average activity concentration of 222Rn of 1000 Bq m23(2, 3). This work has been undertaken to determine the annual-averaged radon concentration in several workplaces in nuclear research centre. MATERIALS AND METHODS The selected workplaces include rooms hosting different activities located in the basement and at different floors of the buildings built with different types of materials. Sampling More than 140 radon measurements were performed in 34 different locations in Algiers nuclear research
centre (Table 1), during a large climatic cycle between March 2010 and June 2013, adding to some scarce measurements performed in 2007(4). This Centre is located at 368460 4700 N and 3830 700 E at an altitude of 108–120 m above the sea level. The geology of the region is formed by sedimentary rocks, basically clay, marls and sandstone. The ambient climate is Mediterranean with cold wet winters (mean December temperature 5–118C, precipitation 126 mm) and hot dry summers (mean May temperature 23–308C, precipitation 7 mm). Experimental procedures Electret ion chambers (EIC), nuclear tracks detectors (NTD) and an AlphaGUARD (AG) continuous radon device were used for the measurements of the radon concentrations: † EICs consisting of ‘S’ chambers equipped with short-term electrets were deployed for 7 d during hot (May–July) and cold (November–January) periods and ‘L’ chambers loaded with long-term electrets were exposed for 6 months during cold (September– February) and hot seasons (March–August). † NTD with LR-115 type II SSNTD film (KODAK, France) in a closed can were exposed for 6 months and then chemically etched in 2.5-M NaOH at 608C for 90 min and counted automatically with a spark counter(5). † Continuous radon monitor (AlphaGUARD PQ2000 PRO) was used continuously every 10 min during 30 h. Air, temperature, barometric pressure and humidity were simultaneously registered.
# The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
Downloaded from http://rpd.oxfordjournals.org/ at Ondokuz Mayis University on November 6, 2014
*Corresponding author: [email protected]
M. AIT ZIANE ET AL. Table 1. Average radon concentrations in different workplaces and status of the ventilation system, level, exposure situation, building materials and measurement technique. Location
BM
V
Exp
MT
Rn (Bq m23)
0 0 0 0 0 21 0 1 4 0 2 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 0 0 1
C S S C C C C C C C C C C S S S S CB CB CB CB CB CB CB CB CB CB CB CB CB CB CB CB C
2 2 2 þ þ þ þ þ þ 2 2 þ 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 þ
E E E E E E E E E E E E E P P P E E E E P E E E E E E E E E E E E E
1,2,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,3,4 1,2,4 4 4 3 1,3,4 1,4 1,2,3,4 3 4 3,4 1,3,4 1,3 4 3 3 1,2,3 3,4 4 1,4 1,4
191 14 14 341 25 63 181 29 5 37 23 10 4 244 602 628 76 13 68 76 240 37 33 14 14 20 25 2 6 7 25 12 36 29
ERn ¼ ðC Rnin Fin Hin þC Rn out Fout Hout ÞtG
ð1Þ
Eg ¼ ðDin Hin þDout Hout ÞtK
ð2Þ
where the subscripts ‘in’ and ‘out’ refer, respectively, to indoor and outdoor locations. CRn (Bq m23) is the average radon concentrations, F is the equilibrium factor (Fin ¼ 0.4, Fout ¼ 0.6)(3, 7) and G is the dose conversion factor (9.0 nSv h21 Bq m23)(7). D (nGy h21) is the measured gamma dose rate, K is the dose coefficient relating to adults equal to 0.7 Sv Gy21(7) and H is the occupancy factor(3) determined assuming 40 working hours week21, throughout the 48 working weeks of the year. Assuming that the workers spent generally 8 h d21 in their working place, the occupancy factor is set equal to 0.22 for Hin and 0.20 for Hout. The time t is in hours for a year (8760 h y21). RESULTS AND DISCUSSION
Level (L): under ground floor: 21, ground floor: 0, first floor: 1, second floor: 2, fourth floor: 4 BM, building materials: C, concrete; CB, clay brick; S, shack. V, ventilation system with (þ), without (2). Exp, exposure situation: E, existing; P, planned. MT, measurement technique: ST-EIC: 1, LT-EIC: 2, AG: 3, NTD: 4.
Gamma dose rates were measured in the examined locations and around the buildings for 8 h using a High-Pressure Ionization Chamber RS-112 at a height of 1 m above the ground and at a distance of 50 m from the outer walls for the outdoor estimation(6). Dose calculations The annual mean effective dose ERn (mSv) due to the radon and its progeny expected to be received by workers staying in the selected locations and the
In all workplaces, pairs of ST and LT type electrets were installed simultaneously to estimate the reproducibility in radon determination. Duplicate measurements were highly correlated and a Students0 t-test for paired samples showed no statistically significant difference ( p ¼ 0.531 and p ¼ 0.524) between results obtained by the two detectors for both types of electrets, respectively. A variation of ,5 % on the average was deduced as previously noticed by Papachristodoulou et al.(8). These measurements are also in good agreement with the corresponding sets of continuous AG measurements, as shown in Figure 1. In this figure, 1-week radon measurements using ST-EIC and the corresponding AG ones averaged in hourly intervals were reported. The observed relationship is linear with a slope equal to 1.0129, and a correlation coefficient R 2 of 0.9981, the results comparable with those given by Denman et al.(9) (slope: 1.0693; R 2: 0.9615). Arithmetic (AM) and geometric (GM) mean radon concentrations and ambient gamma dose rates in outdoor and indoor air averaged over all locations are given in Table 2. Their corresponding annual effective doses, evaluated by using Equations (1) and (2), respectively, are also reported in this table. Radon concentrations and effective doses Indoor radon concentrations in the investigated locations range between 2 and 628 Bq m23, with an AM of 92 Bq m23, while the outdoor radon concentrations vary between 2 and 14 Bq m3, with an AM of 6 Bq m23 (Table 2). Highest radon concentrations were recorded in planned exposure workplaces
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 3 34
L
annual effective dose originating from the gamma radiation source Eg (mSv) are estimated according to the UNSCEAR model(7):
EXPOSURE TO RADON AND GAMMA AT WORKPLACES
Figure.2. Distribution of radon concentration measured in the investigated workplaces.
Table 2. Ambient gamma dose rate and radon concentration in outdoor and indoor air and estimated annual effective doses. Gamma dose rate (nGy h21)
Outdoors Cosmic Terrestrial Total Indoors Cosmic Terrestrial Total
AM+SD
GM
Range
31.2 142.8 + 17.0 174.0 + 17.0
31.2 141.8 173.2
108.8–168.8 140.0–200.0
31.4 + 0.2 282.9 + 792.0 307.9 + 792.1
31.4 128.6 160.2
31.1 –31.6 27.9 –4689.3 52.9 –4714.3
Radon concentration (Bq m23) AM + SD
GM
Range Figure 3. Radon concentration at different levels.
Outdoors Indoors
6+4 92 + 156
5 34
2 –14 2 –628
Gamma effective dose (mSv y21) AM + SD Outdoors Cosmic Terrestrial Total Indoors Cosmic Terrestrial Total
GM
Range
0.04 0.19 + 0.02 0.23 + 0.02
0.04 0.19 0.23
0.15 –0.23 0.19 –0.27
0.04 + 0.00 0.38 + 1.07 0.42 + 1.07
0.04 0.17 0.22
0.04 0.04 –6.33 0.07 –6.36
Radon effective dose (mSv y21) AM + SD Outdoors Indoors
0.04 + 0.02 0.64 + 1.08
GM 0.03 0.23
Range 0.01 –0.09 0.02 –4.35
such as the crushing and grinding units and the ore storage room. Except the latter locations, all values are ,200 Bq m23, in line with the recommendations of the ICRP and the International Atomic Energy Agency (IAEA)(2, 3). The radon concentrations in studied workplaces are given in Figure 2. The hypothesis that values are log–normally(10) distributed is accepted using the Shapiro-Wilk test over all distribution of radon concentrations (x2 ¼ 0.5664, R2 ¼ 0.9916). A general trend of decreasing radon concentration is observed from the basement towards upper floors except for buildings where the radon is due to elevated radium in the construction materials (Figure 3). Therefore, the authors’ future radon measurements will be carried out only on the lowest floor in any building. The high concentrations observed in some workplaces generally located in the basement and due to exceptionally large influxes of radon (building materials, bedrocks, etc.) can be strongly lowered by using ventilation devices.
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Figure 1. Correlation of ST-EIC with AG monitor radon measurements.
M. AIT ZIANE ET AL. Table 3. Ventilation effect. Radon concentration (Bq m23) Location
Ventilation (2)
Ventilation (þ)
A B C
1124 + 319 156 + 52.71 183.7 + 48.72
33.02 + 1.20 63.28 + 20.91 49.06 + 16.09
Figure 4. Mean seasonal radon concentrations.
Results of radon measurements in three such workplaces, performed with and without a ventilation system, are reported in Table 3, with (þ) and (2) notations, respectively. The mean seasonal indoor radon concentration has been estimated including all the investigated locations. It can be noted that the average radon in the winter is higher than in the other seasons because of the closed atmosphere in the buildings during the cold season. Average radon concentrations are lowest in summer, while the average radon concentration in autumn is close to that in spring (Figure 4). The average indoor radon concentration dependence on meteorological parameters including ambient temperature, atmospheric pressure and ambient relative humidity, the values of which were averaged over the sampling periods have been observed and no correlation was found between each of these physical parameters and the radon concentrations. However, the indoor radon concentrations indicate a weak positive correlation (R2 ¼ 0.5527) with the gamma dose rates in the air (Figure 5) due to terrestrial gamma radiation as already observed in the previous paper(11). A more acute observation of the variation of the diurnal indoor radon concentration versus the atmospheric parameters reveals that radon fluxes are in fact somehow positively correlated with the atmospheric pressure and negatively correlated with the relative humidity as shown in Figure 6, which reports the
results obtained in the same workplace during 3 d in August. This result has already been suggested by Rowe et al.(12). However, no correlation has been observed between radon concentrations and temperature or ambient gamma. As a whole, indoor radon concentration measurements are low to moderate in the investigated locations and are below the 1000 Bq m23 reference level recommended by ICRP(2, 3). The average of annual indoor radon concentration in the CRN is 34 Bq m23. The annual effective doses, ERn, obtained by applying Equation (1) are reported in Table 2. The effective dose due to indoor radon varies from 0.02 to 4.35 mSv y21 with a GM value of 0.23 mSv y21. These dose values are also lower than the effective dose values between 3 and 10 mSv y21, given as the range of action levels recommended by the ICRP(2). Gamma dose rates and effective doses Dt indoor and outdoor dose rates (Dt,in and Dt,out, respectively) due to terrestrial gamma radiation have been evaluated from total dose rate measurements D (Din and Dout, respectively) and the cosmic component , following the expression(13): Dt ¼ D ðS Dc;out Þ
ð3Þ
where S the building shielding factor assumed to account for the reduction of cosmic dose rate indoors is equal to 0.8 indoors and 1 outdoor(7). Dc,out is equal to 31.2 nGy h21 in the investigated area, as estimated using Bouville and Lowder formalism(8). The results, displayed in Table 2, show a much higher indoor terrestrial component compared with the outdoor one with a ratio equal to 1.98 (in the range of 0.6 to 23(7)) probably because of the effects of building materials and the existence of planned radon
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Figure 5. Variation in radon concentrations with ambient gamma dose rates.
EXPOSURE TO RADON AND GAMMA AT WORKPLACES
exposure workplaces. Furthermore, the indoor effective doses due to ambient gamma deduced from Equation (2) vary from 0.07 to 6.36 mSv y21 with a GM value of 0.22 mSv y21 even when including the planned exposure workplaces investigated in this work. This value is in the range of 0.3–1.0 mSv y21 established by UNSCEAR from worldwide results(13). CONCLUSION In this study, a good agreement is observed between the values obtained with both detector types suggesting that the more convenient EIC system can be valuably used in the radon campaign with a view to estimate the national radon reference level. The
maximum average radon concentration is equal to 628 Bq m23, while in most workplaces, the average indoor radon concentrations are below the 200 Bq m23 upper limit. Higher concentrations have been observed in workplaces at lower floors in the building except in the workplaces with planned radon exposure. The building materials and bedrock are some of the sources of radon inducing high radon concentrations in a working enclosure which can be strongly reduced by artificial ventilation system. The radon concentration distribution can be well described by a log–normal distribution. This pilot study will be extended to different locations over the country in order to determine the national reference level of radon exposition in workplaces.
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Figure 6. Variation in radon concentrations as a function of time compared with averages of humidity (rh), temperatures (T), atmospheric pressure (P) and ambient gamma.
M. AIT ZIANE ET AL.
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