|Year : 2011 | Volume
| Issue : 2 | Page : 119-128
Preliminary studies on 226 Ra and 232 Th, and 40 K concentrations from quartzite rocks used as building materials
Francis Otoo1, Emmanuel O Darko1, Geoffrey Emi-Reynolds1, Oscar Kwaku Adukpo1, Aba B Andam2
1 Radiation Protection Institute, Ghana Atomic Energy Commission; Graduate School of Nuclear and Allied Sciences, University of Ghana, Legon, Accra, Ghana
2 Graduate School of Nuclear and Allied Sciences, University of Ghana, Legon, Accra, Ghana
|Date of Web Publication||12-Jul-2012|
Radiation Protection Institute, Ghana Atomic Energy Commission; Graduate School of Nuclear and Allied Sciences, University of Ghana, Legon, Accra
Source of Support: None, Conflict of Interest: None
The naturally occurring radioactive materials associated with quartzite rock samples used in the raw form or as aggregates in building materials from different geological locations have been studied using gamma spectrometry. The activity concentration of 226 Ra, 232 Th, and 40 K ranged from 27.64 to 225.78 Bq/kg for 226 Ra, from 20.08 to 72.07 Bq/kg for 232 Th, and from 118.09 to 1443.76 Bq/kg for 40 K. The highest values of 226 Ra and 232 Th occurred in gneiss quartzite from Twin Quarry (TQ), Shai Hills, while the lowest values of 226 Ra and 232 Th were recorded in gneiss quartzite from Rockshell International Quarry (RIQ), Shai Hills. The activity concentration of 40 K varied from 118.09 to 1443.76 Bq/kg, with the highest value in gneiss quartzite from Twin Quarry, Shai Hills, while the lowest activity concentration of 40 K resulting in the micaceous quartzite was recorded from Atomic Hills. The radium equivalent activity (Ra eq ; 98.82-414.35 Bq/kg), the external hazard index (H ex ; (0.27-1.12), gamma activity concentration index (I g ; 0.28-1.48), the absorbed dose rate D in air (11.35-47.72 nGy/h), and the annual effective dose (E T ) (0.08-0.23 mSv/y) were evaluated to assess the radiation hazard to people living in dwellings made of these building materials. The results obtained were found to be within the acceptable limits for public exposure control recommended by the European Commission, International Commission on Radiological Protection (ICRP), and Organization for Economic Cooperation and Development-Nuclear Energy Agency (NEA-OECD).
Keywords: Activity concentration, Gamma spectrometry, NORMs, Quartzite rocks
|How to cite this article:|
Otoo F, Darko EO, Emi-Reynolds G, Adukpo OK, Andam AB. Preliminary studies on 226 Ra and 232 Th, and 40 K concentrations from quartzite rocks used as building materials. Radiat Prot Environ 2011;34:119-28
|How to cite this URL:|
Otoo F, Darko EO, Emi-Reynolds G, Adukpo OK, Andam AB. Preliminary studies on 226 Ra and 232 Th, and 40 K concentrations from quartzite rocks used as building materials. Radiat Prot Environ [serial online] 2011 [cited 2020 Aug 6];34:119-28. Available from: http://www.rpe.org.in/text.asp?2011/34/2/119/98400
| 1. Introduction|| |
There are different types of rocks used for building and construction in the country. Quartzites are the most common metamorphic rocks known to the general public as construction materials for houses, bridges, roads, etc. because of their properties such as fascinating colors, resistance to weathering, textural patterns, crushing strength, abrasive strength, amenability to cutting and shaping without secondary flaws, ability to yield thin and large slabs, and its durability nature. It has been used for centuries for many different purposes in building industries, such as wall cladding, roofing, flooring, and a variety of other interior and exterior applications [1-3] However, studies conducted on rocks in terms of natural radioactivity indicate that radiation exposure is linked to the activity concentrations of the uranium and thorium series and potassium-40, ,,,[,8] and this shows higher activity concentration of the uranium (U), thorium (Th), and potassium (K) compared to other building or geological materials such as soil, sand, clay, ,,,,,,, etc.
Studies on naturally occurring radioactive materials (NORMs) in building and their geological materials are of particular interest because possible human exposure to natural background radiation constitutes the largest source of radiation exposure to the public. , Knowledge of background radiation plays an important role for future radiation impact assessment of human activities associated with NORMs. The radiation exposure of humans may increase for those living in houses or buildings constructed from building materials with radiation dose rate values above normal background radiation levels, which in some cases may be comparative to or even greater than the exposures from the medical use of ionizing radiations. ,,, The radiological implication of living or working in buildings made from such building materials is the increase in external exposure of the body due to gamma-emitting radionuclides. ,,
Radiation exposure due to building materials may be classified into external and internal exposures. The external exposure is caused by direct gamma radiation, whereas the internal exposure is caused mainly by the inhalation and injection of radioactive noble gas radon ( 222 Rn, a daughter product of 238 U) and its short-lived secondary decay products. To assess the radiological hazards to human health, it is important to study the radioactivity levels emitted by the building materials. ,
Therefore, the primary objective of this work was to determine the activity concentrations of the naturally occurring radionuclides of the uranium and thorium series and potassium-40 and their contribution to the annual effective dose equivalent to the public in order to assess the risk from radiation exposure associated with the use of these quartzite rocks as construction or building materials.
| 2. Materials and Methods|| |
2.1. Background of the Study Area
The geology of the study area as shown in [Figure 1] consists; Precambrian Dahomeyan schists, granodiorites, granitic gneiss, and amphibolites to late Precambrian Togo series comprising mainly quartzite, phillites, phylitones, and quartz breccias, and with the residual clays and gravels derived from weathered quartzites, gneiss, and schist rocks, and lateritic sandy clay soils derived from weathered Accraian sandstone bedrock formations.  There are two rainfall patterns within the region for all the climatic zones, but their intensity differ for the climatic zones. The major rainy season occurs between May and July with the peak occurring in June, while the minor rainy season occurs between the months of September to October with the maximum recorded in October.  The mean annual rainfall generally varies between 740 and 890 mm. The mean monthly temperature ranges from 26 o C to 30 o C.  Generally, the study area is characterized by a rugged topography due to the presence of several mountains of different elevations above the sea level. Climatically, some of the areas are arid and the vegetation is scarce, except some grasses and trees, which grow after rainy seasons.
2.2. Sample Collection and Preparation
A total of 144 quartzite rock samples were collected from different geological locations. Samples code and their description are shown in [Table 1] below. The samples were collected from construction industries and open pits where these rocks are mined before sending to the commercial market. Collection was done from the rock open pits, namely Pokuase pit, Weija pit, Ofankor pit, Oyibi pit, Otinibi pit, Dodowa, Atomic Hills pit, and Amasaman, and the quarry industries such as Rockshell International Quarry (RIQ), PW quarry, and Twin Quarry (TQ). The studied rocks were within the ages of 600 million years. The investigated quartzites are mostly used in construction of houses, bridges, and roads in the country. Naming and identification of the quartzite rocks were done at the Department of Geology. The samples were then sent to the Environmental Laboratory of Radiation Waste and Safety Department, Radiation Protection Institute, for analysis. The samples were chiseled out, pulverized, ground, homogenized, air-dried and sieved to a uniform mixture with a particle size of about 5 μm, sealed in 1.0 L Marinelli beaker, and stored at room temperature for a period of 3-4 weeks to allow 238 U and 232 Th decay series to reach radioactive equilibrium with the short-lived progenies. ,,
2.3. Gamma Spectrometry System and Activity Concentration Measurements
The gamma spectrometer system consisting of a high-purity germanium (HPGe) detector coupled to a multichannel analyzer (MCA) with software for data acquisition was used for this work. The detector crystal has a diameter of about 36 mm and thickness of about 10 mm. The crystal is housed in an aluminum canister with a 0.5-mm-thick beryllium entrance window. A lead shield, built with 5-cm-thick lead bricks, surrounds the detector to reduce background from building materials and cosmic rays. The detector is coupled to a Canberra 1510 signal processing unit which contains the power supply, amplifier, and analog-to-digital converter. Digitized counts are collected in a Canberra S100 multichannel analyzer. Spectrum acquisition and analysis are performed with APTEC software. The detector was cooled by down to about 77 K by liquid N 2.
The energy and efficiency calibration of the system were carried out using solid water in 1.0 L Marinelli geometry from Deutscher Kalibrierdienst (DKD) of Germany. The standard solution contains the following radionuclides with the corresponding energies: 241 Am (60 keV), 109 Cd (88 keV), 57 Co (122 keV), 139 Ce (1656 keV), 203 Hg (279 keV), 113 Sn (391.69 keV), 85 Sr (514 keV), 137 Cs (662 keV), 88 Yt (898 keV and 1836 keV), and 60 Co (1173 keV and 1333 keV). The samples were counted for 36,000 s. Background measurements were also made for the same period and subtracted from the samples ,, with the high-resolution gamma ray spectrometer made up of HPGe detector and counting assembly. The Canberra S100 MCA and APTEC software program were used for spectrum acquisition and analysis. The weight of each sample, sampling date and time, and counting date and time were recorded. Corrections for density and inhomogeneity were also made. ,,
The activity concentration Ac (Bq/kg) of each radionuclide in any given sample was calculated from the spectrum using the following analytical expression: 
where, N sam (kg) is the mass of sample, N sam (cps) is the net peak area for the sample in peak range, P(E) is the gamma emission probability, η(E) is the counting time in seconds, and η(E) is the photopeak efficiency which had been obtained from the standard solution.
Where the parent nuclides were in secular equilibrium with their daughter nuclides, the activity concentrations of the parent nuclides were estimated from their respective daughter concentrations. For instance, the transition lines (609.31, 1764.61 keV) of 214 Bi and (583.32, 2614.57 keV) of 208 Ti were used to determine the activity concentrations of 226 Ra and 232 Th, respectively. 40 K was determined directly with its only 1460.75 keV peak transition line.
| 3. Results and Discussion|| |
The quartzite samples were studied for the natural radionuclides of 226 Ra, 232 Th, and 40 K. The activity concentrations of each of the samples together with their corresponding total uncertainty were calculated are summarized in [Table 2].
|Table 2: Activity concentrations (Bq/kg) of 226Ra, 232Th, and 40K in the investigated samples|
Click here to view
The activity concentration of the studied quartzites ranged from the 27.64 to 225.78 Bq/kg for 226 Ra and from 20.08 to 72.07 Bq/kg for 232 Th, respectively. The highest activity concentration levels of the 226 Ra and 232 Th were 225.78 and 72.07 Bq/kg, respectively, which occurred in gneiss quartzite from TQ, Shai Hills, while the lowest values (27.64 and 20.08 Bq/kg) of 226 Ra and 232 Th, respectively, were recorded in the gneiss quartzites from RIQ, Shai Hills. The activity concentration of the 40 K varied from 118.09 to 1443.76 Bq/kg, with the highest value occurring in gneiss quartzites from TQ, Shai Hills, while the least activity concentration of 40 K resulted in micaceous quartzites from Atomic Hills. 40 K is the more significant compared to 226 Ra and 232 Th and contributes to higher gamma radiation exposure to the public.  Both average and activity concentration levels of 226 Ra, 232 Th, and 40 K in the studied samples were compared as shown in [Figure 2] with those reported in studies from other countries [Table 3] and the global average for soil of 226 Ra (33 Bq/kg), 232 Th (45 Bq/kg), and 40 K (420 Bq/kg) 16 , and building materials of 226 Ra (50 Bq/kg), 232 Th (50 Bq/kg), and 40 K (500 Bq/kg).  It was found out that radionuclide of 40 K (118.09, 203.31, 324.71, and 371.68 Bq/kg) of the fresh foliated quartzite, micaceous from Atomic Hills, micaceous quartzite from McCarthy Hills, and moderately weathered quartzites from Weija recorded individual values lesser than both the recommended levels for soil and building materials from UNSCEAR, 1993 and 2000, while 226 Ra (31.05 and 27.64 Bq/kg) of the gneiss from the PW and RIQ quarries of Shai Hills also had values lesser than the recommended levels. All the studied samples from the Ofankor Hills and Dodowa also recorded activity concentration of 232 Th lesser than the recommended levels from UNSCEAR for soil and building materials, respectively, while radionuclide 232 Th in the quartz vein, moderately weathered quartzites, highly weathered quartzite, micaceous quartzite from Amansam, Weija, Pokuase, Atomic Hills, McCarthy Hills, Oyibi, Otinibi, and gneiss quartzite from Shai Hills recorded some values lesser than both the recommended levels from UNSCEAR, 1993, 2000, as shown in [Table 2]. The average values of 232 Th calculated were lesser than the UNSCEAR recommended levels of 232 Th, with the exception of the highly weathered and gneiss quartzite of values 46.37 and 123.69 Bq/kg, respectively. The compared data show that radioactivity in rocks varies from one country to another. It is also important to mention that these values were not for the whole country as given in [Table 3], but for the areas from which the samples were collected. The activity concentrations of the radionuclides of the present study were within the range of other published works with the exception of reports from Egypt and Brazil.
|Table 3: Comparison of the activity concentration (Bq/kg) of the rocks studied with other rock samples|
Click here to view
3.1. Radium equivalent activity
The radiological or health hazards associated with natural radioactivity in the quartzite rocks used as building materials were assessed using radium equivalent activity (Ra eq ). It is the most frequently and widely used index to establish the radiation hazards with reference to the external gamma dose and internal dose due to radon, using the estimated activity concentration of the radionuclides of 226 Ra, 232 Th, and 40 K. ,,
where A C (Ra) , A C (Th), and A C (K) are the activity concentration activities in Bq/kg of 226 Ra, 232 Th, and 40 K, respectively.
This hazard index is based on the assumption that 370 Bq/kg of 226 Ra, 259 Bq/kg of 232 Th and 4810 Bq/kg of 40 K produce the same gamma ray dose rate, , which implies that a radium equivalent of 370 Bq/kg in building materials will produce an external exposure of about 1.5 mSv/y to the public. , The Ra eq equivalent values calculated for the same quartzite rocks varied from different geological locations, which indicate that 226 Ra, 232 Th, and 40 K are not uniformly distributed in quartzite rocks in the sampling areas. The calculated average values of the Ra eq for each of the investigated samples ranged from 199.06 to 225.37 Bq/kg, with the highest value occurring in quartzite samples while the lowest Ra eq values were recorded in moderate weathered quartzite. The calculated individual Ra eq of each of the samples also ranged from 98.82 to 414.35 Bq/kg, with the maximum value recorded in the gneiss quartzite (414.35 Bq/kg) from the TQ, Shai Hills, while the minimum value was recorded in the gneiss quartzite (98.53 Bq/kg) from the RIQ, Shai Hills. All the calculated average Ra eq values of the studied samples were lesser than the recommended value of 370 Bq/kg for building materials shown in [Figure 3]. The calculated individual radium activity recorded shows that most of the values were lesser than the recommended level, with the exception of the three gneiss quartzite samples from TQ, Shai Hills (384.32 Bq/kg, 379.75 Bq/kg, and 414.33 Bq/kg), and quartz vein from Ofankor (395.54 Bq/kg).
3.2. External Hazards Index (H ex )
The external hazards index (H ex ) is used to determine the suitability of a material and estimate the external radiation exposure to human health if that material is used to construct houses. The external hazard index was calculated using the following equation: ,
where A C (Ra), A C (Th), and A C (K) are the activity concentrations of 238 U, 232 Th, and 40 K, respectively, expressed in Bq/kg.
The external hazards index value must be less than unity in order to keep the external gamma dose of building materials to a radiation exposure limit of 1.5 mSv. ,, The external hazards index ranged from 0.27 to 1.12 and its average value also ranged from 0.54 to 0.68) as shown in [Table 4], with the gneiss quartzite from RIQ, Shai Hills, recording the lowest value while the highest external index occurred in gneiss from TQ, Shai Hills. Both the calculated average and individual values obtained for external hazard index of the quartzite rock were lesser than the recommended limit with the exception of gneiss quartzite samples from TQ with values (1.04, 1.03, and 1.12) more than unity.
|Table 4: Gamma index proposed by the European Commission (1999) taking into account typical ways and quantities in which the materials are used in building materials|
Click here to view
3.3. Gamma Activity Concentration Activity Index (I g )
There is also the radiation hazard threat to respiratory organs due to 222 Rn, decay product of 226 Ra, and its short-lived decay product. According to most recent regulations and especially recommendation No. 112 issued by the European Union (EU) in 1999, 18 building materials should be exempted from all restrictions concerning their radioactivity, if the excessive gamma radiation due to those materials causes an increase in the annual effective dose received by an individual by a maximum value of 0.3 mSv. Effective doses exceeding the dose criterion of 1 mSv/y should be taken into account in terms of radiation protection. It is therefore recommended that controls should be based on a dose range of 0.3-1.0 mSv/y, which is the building material gamma dose contribution to the dose received outdoors. 3 The gamma activity concentration index (I g ) is derived to determine whether the dose criterion recommended by EU (1999) associated with these radionuclides in building materials is met. In order to examine that building materials meet these two dose criteria, the following gamma activity concentration index (I g ) proposed by EU (1999) was used:
where A C (Ra), A C (Th), and A C (K) are the activity concentrations of 238 U, 232 Th, and 40 K, respectively, expressed in Bq/kg, in the building materials. 
The index should not exceed the values given in [Table 4], depending on the dose criterion, and the way in which the material is used and the amount of the material used in building.  For superficial and other building materials with restricted fractional mass usage, such as those studied in this work, the exemption dose criterion (0.3 mSv/y) corresponds to a gamma index, I g ≤ 2, while the dose criterion of 1 mSv/y is met for I g ≤ 6.  The gamma activity concentration index and its average values of the samples are shown in [Table 5]. The gamma activity concentration index of each of the samples ranged from 0.28 to 1.48, with the gneiss quartzite from PW, Shai Hills, recording the lowest value while the highest external index occurred in gneiss from TQ, Shai Hills. For superficial and restricted use of the rock samples in buildings, according to the present study, all the investigated samples do not exceed the recommended upper limit and the recommended exemption level for exposure to external gamma radiation proposed by European Commission.
|Table 5: Radium equivalent activity (Raeq), gamma activity concentration index (Ig), external hazard index (Hex), absorbed dose rate (D), and annual effective dose (ET) for the investigated samples|
Click here to view
3.4. Absorbed Dose Rates and Annual Effective Doses
The absorbed dose rate in air in a room [D(nGy/h)] was calculated using the specific dose rates (EC, 1999) of 226 Ra, 232 Th, and 40 K from their mean activity concentration in the quartzite with the assumption that other radionuclides such as 137 Cs, 90 Sr, and 235 U decay series are negligible since their contribution to the total dose in the environmental radioactivity is very minimal. ,, For superficial materials such as marble, ceramic, granite, and roofing tile, the dose rate is given as: ,
where,0.12, 0.14, and 0.0096 are the dose constants for 226 Ra, 232 Th, and 40 K, respectively, and A C (Ra), A C (Th), and A C (K) are the activity concentrations of 226 Ra, 232 Th, and 40 K, respectively, expressed in Bq/kg, in the building materials.  The absorbed dose rate in air and its average values calculated from the investigated quartzite rocks as a building material ranged from 11.35 to 47.72 nGy/h, with the lowest and highest values occurring in gneiss quartzite from TQ and RIQ from Shai Hills, respectively, while the average values also varied from 22.90 to 29.01 nGy/h with the lowest and highest values occurring in moderately weathered and gneiss quartzite, respectively. The calculated absorbed dose rate and its average values were lesser than the worldwide average value of soil (55 nGy/h)  and lay within UNSCEAR reported average value (18-93 nGy/h). ,
The annual effective dose (ET ) in mSv/y to the public from the measured radioactivity associated with the quartzite rock samples used for building materials was calculated according to the recent regulation and recommendation No. 112.  The effective dose rate in air was calculated from the formula.  The annual effective dose (ET ) in mSv/y is given as:
where D is in nGy/h, 0.7 Sv/Gy is the effective absorbed dose conversion factor, and 7000 h is the annual exposure time. The annual effective dose varied from 0.08 to 0.23 mSv/y, while the average effective dose also ranged from 0.11 to 0.14 mSv/y. Both the annual effective dose and its average values were lesser than the limit defined by the European Commission, 1999. The values were also found to be lesser than the limit for public exposure control set by the International Commission on Radiological Protection (ICRP) 60 and Organization for Economic Cooperation and Development-Nuclear Energy Agency (NEA-OECD). ,
| 4. Conclusion|| |
NORMs and their related radiation hazards in quartzite rocks sample used as a building material within Greater Accra region of Ghana have been studied using gamma spectrometry. The activity concentration levels of various radionuclides of 226 Ra, 232 Th, and 40 K investigated were found to be normal and within the average worldwide ranges. The radium equivalent, external hazards index, gamma activity concentration index, absorbed dose rate in air, and annual effective doses calculated were generally found to be within the values found in other countries, with the exception of three samples which showed greater than the recommended level for radium equivalent activity. The gamma activity concentration index was lesser than the limit recommended for both exemption and protection of building materials. The values were also found to be within the limit for public exposure control set by the EC (1999), ICRP 60, and NEA-OECD. ,, Therefore, the rock samples do not pose any radiation hazard to health when used in building or construction of houses and other facilities.
| 5. Acknowledgments|| |
The authors are grateful to the Radiation Protection Institute of the Ghana Atomic Energy Commission for the use of their facilities for this study, and Mr. Prince Ofori Amponsah of Department of Geology, University of Ghana, Legon, Accra, Ghana, is acknowledged for his assistance in the identification and clarification of the rock samples prior to the analysis.
| References|| |
|1.||Anjos RM, Veiga R, Soares T, Santos AM, Aguiar JG, Frasca´ MH, et al. Natural radionuclide distribution in Brazilian commercial granites. Radiat Meas 2005;39:245-53. |
|2.||Iqbal M, Tufail M, Mirza SM. Measurement of natural radioactivity in marble found in Pakistan using a NaI(Tl) gamma-ray spectrometer. J Environ Radioact 2000;51:255-65. |
|3.||Tzortzis M, Tsertos H, Christofides S, Christodoulides G. Gamma radiation measurements and dose rates in commercially-used natural tiling rocks (granites). J Environ Radioact 2003;70:223-5. |
|4.||El-Arabi AM. 226 Ra, 232 Th and 40 kconcentrations in igneous rocks from eastern desert, Egypt and its radiological implications. Radiat Meas 2007;42:94-100. |
|5.||Joshua EO, Ademola JA, Akpanowo MA, Oyebanjo OA, Olorode DO. Natural radionuclides and hazards of rock samples collected from Southeastern Nigeria. Radiat Meas 2009;44:401- 4 |
|6.||Tufai MN, Ahmad SM, Mirza NM, Khan HA. Natural radioactivity from the building materials used in Islamabad and Rawalpindi, Pakistan. Sci Total Environ 1992;121:283-91. |
|7.||Walley El-Dine W, El-Shershaby A, Ahmed F, Abdel-Haleem AS. Measurement of radioactivity and radon exhalation rate in different kinds of marbles and granites. Appl Radiat Isot 2001;55:853-60. |
|8.||Abd El-Naby HH, Saleh GM. Radioelement distribution in the Proterozoic granites and associated pegmatites of Gabal El Fereyid area, Southeastern Desert, Egypt. Appl Radiat Isot 2003;59:289-99. |
|9.||Arafa W. Specific activity and hazards of granite samples collected from Eastern Desert of Egypt. J Environ Radioact 2004;75:315-27. |
|10.||Fokianos K, Sarrou I, Pashalidis I. Increased Radiation Exposure by Granite used as Natural Tiling Rock in Cypriot Houses. Radiat Meas 2007;42:446-8. |
|11.||Hussain HH, Hussain RO, Yousef RM, Shamkhi Q. Natural radioactivity of some local building materials in the middle Euphrates of Iraq. J Radioanal Nucl Chem 2010;284:43-7. |
|12.||Ngachin M, Garavaglia M, Giovani C, Kwato Njock MG, Nourreddine A. Assessment of natural radioactivity and associated radiation hazards in some Cameroonian building materials. Radiat Meas 2007;42:61-7. |
|13.||Otoo F, Adukpo OK, Darko EO, Emi-Reynolds G, Awudu AR, Ahiamadjie H, et al. Assessment of Natural Radioactive Materials in Building Materials Used along the Coast of Central Region of Ghana. Res J Environ Earth Sci 2010;3:261-8. |
|14.||Yeboah J, Boadu M, Darko EO. Natural radioactivity in soil and rocks within the Greater Accra Region of Ghana. J Radioanal Nucl Chem 2001;249:629-32. |
|15.||UNSCEAR. United Nations Scientific Committee on the Effects of Atomic Radiation Sources and Effects of Ionizing Radiation. Report to Assembly with Annexes. UNSCEAR, New York, 2000. |
|16.||UNSCEAR. United Nations Scientific Committee on the Effects of Atomic Radiation Sources and Effects of Ionizing Radiation. Report to Assembly with Scientific Annexes. UNSCEAR, New York, 2010. |
|17.||EC. European Commission. Radiation Protection Unit, Radiological protection principles concerning the natural radioactivity of building materials. Radiat Prot 1999;112;1-16 |
|18.||Lee EM, Menezes G, Finch EC. Natural radioactivity in building materials in the Republic of Ireland. Health Phys 2004;84:378-83. |
|19.||O¨rgu¨n Y, Altinsoy N, Gu¨ltekin AH, Karaham G, Celebi N. Natural radioactivity levels in granitic plutons and groundwaters in Southeast part of Eskisehir, Turkey. Appl Radiat Isot 2005;63:267-75. |
|20.||Beretka J, Mathew PJ. Natural radioactivity of Australian building materials, industrial wastes and by-products. Health Phys 1985;48:87-95. |
|21.||Florou H, Kritidis P. Gamma radiation measurements and dose rate in the coastal areas of a Volcanic Island, Aegean Sea, Greece. Radiat Prot Dosim 1992;45:277-9. |
|22.||Leung JK, Tso MY, Ho CV. Behavior of 222 Rn and its progeny in high-rise Building Materials. Healthy Phys 1998;75:303-12. |
|23.||Petropoulos NP, Anagnostakis MJ, Simopoulos SE. Photon attenuation, natural radioactivity content and radon exhalation rate of building materials. J Environ Radioact 2002;61:257-69. |
|24.||Amrani D, Tahtat M. Natural Radioactivity in Algerian building materials. Appl Radiat Isot 2001;54:687-9. |
|25.||Kesse GO . The Mineral and Rock Resources of Ghana. Rotterdam/Boston: A.A/ Balkema; 1985. |
|26.||Dickson KB, Benneh G . A New Geography of Ghana. London: Longmans Group Limited; 2004. |
|27.||Khan K, Aslam M, Orfi SD, Khan HM. Norm and associated radiation hazards in bricks fabricated in various localities of the North-West Frontier Province (Pakistan). J Environ Radioact 2002;58:59-66. |
|28.||Kumar A, Kumar M, Singh B, Singh S. Natural activities of 238 U , 232 Th and 40 K in some Indian building materials. Radiat Meas 2003;36:465-9. |
|29.||Darko EO, Tetteh GK, Akaho EH. Occupational radiation exposure to NORMS in a goldmine. Am J Radiat Prot Dosim 2005;114:2-23. |
|30.||Beck HL, Decompo J, Gologak J. In situ Ge (ii) and NaI(Tl) gamma ray spectrometry. Health and Safety Laboratory AEC, Report HASL 258, New York, 1972. |
|31.||Xinwei L, Lingqing W, Xiaodan J, Leipeng Y, Gelian D. Specific activity and hazards of Archeozoic-Cambrian rock samples collected from the Weibei area of Shaanxi, China. Radiat Prot Dosimetry 2006;118:352-9. |
|32.||UNSCEAR. United Nations Scientific Committee on the Effects of Atomic Radiation. Exposure from Natural Sources of Radiation. United Nations, New York, 1993. |
|33.||Ahmed NK, Abbady A, El Arabi AM, Michel R, El-Kamel AH, Abbady AG. Comparative study on the natural radioactivity of some selected rocks from Egypt and Germany. Indian J Pure Appl. Phys 2006;44:209-15. |
|34.||Kilic AM, Aykamis AS. The natural radioactivity levels and radiation hazard of pumice from the East Mediterranean Region of Turkey. Bull Eng Geol Environ 2009;68:331-8. |
|35.||Wallova G, Kamala KA, Wallner G. Determination of naturally occurring radionuclides in selected rocks from Hetaunda area, central Nepal. J Radioanal Nucl Chem 2010;283:713-8. |
|36.||Hayambu P, Zaman MB, Lubaba NC, Munsanje SS, Muleya D. Natural radioactivity in Zambian building materials collected from Lusaka. J Radioanal Nucl Chem 1995;199:229-38. |
|37.||Krstic´ D, Nikezic´ D, Stevanovic´ N, Vuc¡ic´ D. Radioactivity of some domestic and imported building materials from South Eastern Europe. Radiat Meas 2007;42:1731-6. |
|38.||UNSCEAR. Sources, effects and risks of ionizing radiation. United Nations Scientific Committee on the effects of atomic radiation. Report to the General Assembly on the Effects of Atomic Radiation, United Nations, New York, 1988. |
|39.||NEA-OECD. Organization for Economic Co-operation and Development-Nuclear Energy Agency. Report exposure to radiation from natural radioactivity in building materials. Paris, 1979. |
|40.||Jacob P, Paretzke HG, Rosenbaum H, Zankl M. Effective dose equivalents for photon exposure from plane sources on the ground. Radiat Prot Dosimetry 1986;14:299-310. |
|41.||Kocher DC, Sjoreen AL. Dose-rate conversion factors for external exposure to photon emitters in soil. Health Phys 1985;48:193-205. |
|42.||Yang YX, Wu XM, Jiang ZY, Wang WX, Lu JG, Lin J, et al. Radioactivity concentration in soils of the Xiazhuang granite area. China. Appl Radiat Isot 2005;63:255-9. |
|43.||43 ICRP 60. Recommendation of the International Commission on Radiological Protection. Oxford: Pergamon Press; 1991. |
[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]