STUDY OF RADON LEVELS AND NATURAL RADIOACTIVITY IN ENVIRONMENT
s\^ <#• ABSTRACT OF THE >^ THESIS SUBMITTED FOR THE AWARD OF THE DEGREE OF ©octor of pjilos;opI)P
(( IN APPLIED PHYSICS w \
BY AJAY KUMAR MAHUR
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DEPARTMEIMT OF APPLIED PHYSICS Z. H. COLLEGE OF EIMGINEERING & TECHNOLOGY ALIGARH MUSLIM UNIVERSITY ALIGARH (INDIA) 2008 »•• t:i<-: Abstract 1
The exposure of human beings to ionizing radiation from natural sources is a continuing and inescapable feature of life on earth. For most individuals, this exposure exceeds that from all man-made sources combined. There are two main contributors to natural radiation exposures: high-energy cosmic ray particles incident on the earth's atmosphere and radioactive nuclides that originated in the earth's crust and are present everywhere in the environment, including the human body itself. Radon is a noble gas in the uranium decay series with a fairly long half life of 3.8 days. Being an inert gas it can easily disperse into the atmosphere as soon as it is released. The solid alpha active decay products of radon (^'^Po, ^'"Po) become airborne and attach themselves to the dust particles, aerosols and water droplets in the atmosphere. When inhaled, these solid decay products along with air may get deposited in the tracheo bronchial (T-B) and pulmonary (P) region of lungs resulting in the continuous irradiation by a-particles of the cells which may cause lung cancer. Radon is the problem in all types of homes, including old homes, new homes, drafty homes, insulated homes, homes with basements and homes without basements. Measurements of indoor radon are of importance because the radiation dose to human population due to inhalation of radon and its daughters contributes more than 50% of the total dose from natural sources and large scale studies have been carried out world wide. On the other hand there exists only a few studies relating to passive measurements of thoron. It is assumed that the inhalation dose to the human beings from thoron and its progeny is negligible although recent studies in many countries have revealed that this may not be entirely correct. It is well known that exposure of population to high concentrations of radon and its daughters for a long period leads to pathological effects like the respiratory functional changes and the occurrence of lung cancer. In homes the predominant source of radon in indoor air is the soil beneath structures, but building materials and water used in the homes and in a few cases natural gas may also contribute. The concentrations of radium in soil and in rocks vary several orders of magnitude. This variation in source strength results in the variation of radon V concentrations among dwellings. Keeping the radiation hazards of radon for general population in mind, it is quite important to make a systematic study of the indoor radon concentration in Indian dwellings. For this purpose, radon measurements have been carried out in a number of dwellings in the cities of different states of India. Natural radioactivity is wide spread in the earth's environment coming from Uranium (^^^U) and Thorium p^Th) series and Potassium ('*°K), existing in various geological formations like soils, rocks, plants, water and air. Radiological implication of these radionuclides is due to the gamma ray exposure of the body and a- irradiation of lung tissues from inhalation of radon and its daughters. The assessment of gamma radiation dose and radon exhalation rate from natural sources is of particular interest as natural radiation is the largest contributor to external dose of the world population. In the present study, a low level gamma ray spectrometric set up at the National Geophysical Research Institute, Hyderabad (India) and a coaxial n-type HPGe detector (EG&G, ORTEC, Oak Ridge, USA) at Inter-University Accelerator Centre, New Delhi (India) were used for the estimation of activity concentrations of U, Th and K concentration (Cu, Cxh and CK) in the coal, fly ash, rock, soil and sand samples. In few coal, fly ash and soil samples fission track registration technique using thermal neutrons in "APSRA" reactor at Bhabha Atomic Research Centre Mumbai India, was used for the estimation of U concentration. Also Radium concentration was measured using SSNTD's. Radiation dose and health risk have been estimated from the activity concentration of natural radionuclides. This thesis is divided into five chapters. Chapter-I This chapter describes a brief review of literature and gives an account of the history of radon and thoron and its health hazard effects, the indoor radon sources, factors affecting indoor radon concentration levels and the applications of radon measurements. A brief description of meteorological parameters, radon induced health effects, risk of radon exposure at work places. Introduction of natural radioactivity and health effects due to radioactivity is given. This chapter also contains definitions and discussion of radiation levels and their effects and definitions action level, dose limit, effective dose. Equilibrium Equivalent Concentration of radon (EEC radon). Equilibrium Equivalent Concentration of thoron (EEC thoron). Potential Alpha Energy Concentration (PAEC), Working Level (WL), Woricing Level Month (WLM), Indoor internal exposure due to radon inhalation, Radium equivalent activity ( Raeq), Absorbed gamma dose rate (D) and External (Hex) and Internal (H,n) hazard index . Chapter-II
A brief description of the historical development of Solid State Nuclear Track Detectors (SSNTDs), criteria for track formation in polymeric film (LR-115 type II Solid state nuclear track detector) and revelation of tracks is given in this chapter. This chapter gives an account of various instantaneous and time integrated radon measurement techniques. Tracks etch technique using Solid State Nuclear Track Detectors is one of the most widely used technique for radon measurement. The principle of detection consists of the damage imparted in the detector material by alpha particles from radon and its decay products which can be observed under optical microscope. Twin cup radon dosimeter was used in present study for the measurement of indoor and outdoor radon concentrations. Alpha sensitive plastic track detector (pelliculable LR-115 Type II Manufactured by Kodak Pathe, France) is used. It is a 12 ^m thick film red dyed cellulose nitrate emulsion coated on inert polyester base of 100 fim thickness and has maximum sensitivity for alpha particles, fission fragments and ionizing particles with high enough LET. Radon exhalation rale is of prime importance for the estimation of radiation risk from various materials. "Sealed Can Technique" was used for radon exhalation measurements in solid samples. A low level gamma ray spectrometric set up at National Geophysical Research Institute, Hyderabad was used for estimation of the natural radionuclides, uranium thorium (^^^Th) and potassium ("^K) in coal and fly ash samples. Gamma ray spectrometric measurements were Carried out at Inter-University Accelerator Centre, New Delhi using a coaxial n-type HPGe detector (EG&G, ORTEC, Oak Ridge, USA) for estimation of the natural radionuclides, uranium (^^*U), thorium (^^^Th) and potassium ( ^) in rock and soil samples. Fission track registration technique was used for the estimation of U-concentration. Chapter-m In this chapter the results of measurements of radon and its concentration in a large number of dwellings carried out in following: (i) In about 45 dwellings of the cities of Baijnath and Palampur (Himachal Pradesh) to assess the variability of expected exposure of the population to radon and its progeny, (ii) In three towns: Eravipuram, Panmana and Thankassery in Kollam district in the south west of Kerala. Thankassery and Panmana are in the vicinity of the High Back Ground Area (HBRA) and in Eravipuram about five to six Km away from the High Back Ground Area, (iii) In some villages around the Nuclear Atomic Power Plant (NAPP) at Narora, is located in seismic zone and is about 150 km away from New Delhi, capital of India, (iv) In Bhatinda (Punjab) near a thermal power plant were selected for measurements of indoor radon levels. (v) Surrounding the National Hydroelectric Power Corporation (NHPC) project at upper Siang in Arunachal Pradesh, India.This project is situated at Upper Siang, the hilly region of Arunachal Pradesh and is country's largest power project and the world's third largest. (vi) In Kutch district of Gujrat state, severely jolted by a powerfijl earthquake on the morning 26 January 2001. The earthquake took a tool of 20,072 human lives, killed 21551 cattle and inflicted various grades of damage to about 10.8 lakh houses in 7904 villages. (vii) In Jaduguda mining area of Jharkhand. Jharkhand state of India is rich in minerals and is called the store house of minerals. In addition to uranium deposits at Jaduguda, there are huge deposits of bauxite, mica and coal along with iron, copper, chromites, tungsten, lime stone, feldspar and quartz etc. Solid State Nuclear Track Detectors (SSNTD's) based twin chamber dosimeters were also used for estimating radon (^^^Rn) and Thoron (^^°Rn) gases and their progeny concentration in the dwellings of five cities and some dwellings surrounding the Narora Atomic Power Station (NAPS). The dosimeters employ two LR-115 type II peliculable. cellulose nitrate detector films inside each of the two chambers fitted with filter and polymeric membrane for the discrimination of radon and thoron gas and a third detector is placed externally for progeny measurements. Chapter-IV Measurements of natural radioactivity and radiation doses were carried out on the following material samples having wide applications, collected from different places and parts of the country: (i) Coal and fly ash samples, collected from different thermal power stations at Kolaghat, Durgapur, Bandel and Kasimpur situated in West Bengal and Uttar Pradesh states of India. Measurements have been made to estimate the enhancement of naturairadioactivity in fly ash due to coal combustion. The thermal power plants all over the country produce a large quantity of fly ash which if not utilized or properly disposed off, may become one of the greatest radiation menace to the nation and its inhabitants. (ii) Rock and soil samples, collected from different places of Jaduguda uranium mines in Singhbhum shear zone in the state of Jharkhand, India. (iii). Sand samples containing heavy minerals, collected from Chhatrapur and Erasama beach placer deposit, situated in a part of the eastern coast of Orissa, a newly discovered High Natural Background Radiation Area (HBRA) in India. An attempt has been also made to determine the effective radium content using LR-115 plastic track detectors in the sand samples collected from Chhatrapur beach of Orissa State (India) and also of some samples collected from rivers. Chapter-V "Sealed can technique" was used for the measurement of radon exhalation from: Coal, fly ash, soil, rocks and sand samples collected from different parts of India. Radon exhalation rates were also measured in soil and phospho-gypsum samples, colleted from a large industrial complex which is located in the proximities of Huelva town, south west of Spain. A large industrial wastes disposal site where two phosphate rock processing plants release their wastes is located close to Huelva town, SW of Spain. It has been partially submitted to restoration works as a preliminary step in a possible decommissioning process.
5tfS.bV In the present study we have also made measurements for radon exhalation rate in different building materials like ceramic tiles, granite, bricks and marble etc., commonly used for building construction in this region of the state of Uttar Pradesh of India. Some measurements were made for the samples from the Southwest coast of Kerala. Kerala State in India is known to have very high levels of natural background radiation owing to the rare earths rich monazite sand available in large amount. Sand present in the region is an orthophosphate of thorium and rare earths and typically contains about 9% thorium oxide and 0.35% uranium oxide. Here exists a unique situation where a large population is being exposed to a high level radiation all through their life-span. STUDY OF RADON LEVELS AND NATURAL RADIOACTIVITY IN ENVIRONMENT
THESIS SUBMITTED FOR THE AWARD OF THE DEGREE OF ©octor of ^Ijila^opljp IN APPLIED PHYSICS
BY AJAY KUMAR MAHUR
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DEPARTMENT OF APPLIED PHYSICS Z. H. COLLEGE OF ENGINEERING & TECHNOLOGY ALIGARH MUSLIM UNIVERSITY ALIGARH (INDIA) 2008 Mia T7061 iniiwiiiii(iinimiiiiiiiiiininiiniMiiiiiiii HK laimi^ Miiitwfflfwttmit^^ Department of Applied Physics, Z. H. College of Engineering & Technology Aligarh Muslim University Aligarh-202002, INDIA CERTinCATE Tim is to certify tkat rcaorch wark preinted • the IVD. thesis CBlil^ "Study of Radon Levels and Natural Radioactivity in Environment* submitted b^ Mr. Ajaj Knaar MaJkw fcr the mmmrd af the decree af i Philosophjr •• Appicd Fhpicsy Fanritjr vf Emf^eamf, A \SmmctwHtfy. ASg^M^ is the wr^^al WMrfc carried avt hf the siqierTNM aad guidance. This wMrh h» Bat beea sdbautted ia part ar lid dearer «n PraL RajcMlni Prasad (Sapervisar) ,\^ CCa^npcrviMr) Department of Applied Pl^sks X^ Department eXAp^laied Physics Aligarh Muslim University', Aiigarii Madim lliiiv€isi1Qr, Aligs«ii-2([m»i2, INDIA Aligarii-202002. INDIA Acknowledgements I would like to express my deep sense of gratitude to my Ph.D supervisors, Dr. Ameer Azam (Reader) and Prof. Rajendra Prasad, former Chairman, Department of Applied Physics, Z. H. College of Engineering and Technology, Aligarh Muslim University, Aligarh. They have shown me the path and lightened it for me through their useful suggestions, thorough discussion and interpretation of results. I would like to convey my sincere gratitude to Prof Rajendra Prasad who introduced me to the subject and whose learned guidance and support at every step has helped me in the completion of this study. His indepth knowledge, meticulous attention to details, constant encouragement and lively criticism of this work done proved invaluable. I sincerely acknowledge that I have learnt the importance of keeping one self constantly updated and abreast of in the field. I express my deepest gratitude to Prof, Alimuddin, Chairman, Department of Applied Physics, Z. H. College of Engineering and Technology, Aligarh Muslim University for providing me the experimental facilities for this work and to Prof Javed Husain, Prof K. M. Lai, Prof AJim Hussain Naqvi, Dr. Shakeel Khan and Dr. M. K. Bhardwaj and all academic and non-academic staff of the Department of Applied Physics, Aligarh Muslim University for their constant support and help. I am thankfiil to Dr. Amit Roy, Director, Inter University Accelerator Centre (lUAC) New Delhi, for providing experimental facilities at lUAC, for natural radioactivity measurements. I express my deepest gratitude to Dr. R. G. Sonkawade, Senior Scientist, lUAC, New Delhi for helping me in natural radioactivity measurements. I take this opportunity to express my deepest gratitude to Prof D. Sengupta, Department of Geology and Geophysics, I.I.T. Kharagpur for his constant encouragement, moral support and many fruitful suggestions during the course of this thesis work. I am also thankful to him for providing me some samples of fly ash, rocks, soil and building construction materials. I also wish to express my sincere thanks to Dr. R. Swamp, former Head Physics Department, D. S. College, Aligarh. I wish to express my sincere thanks to all editors, publishers and their honorable referees who have published our research papers. My sincere thanks are my seniors Dr. Rajesh Kumar, Dr. P. J. Jojo, Dr. A. K. Singh and Dr. Ashawani Kumar for their enlightening comments and suggestions during this work. Special thanks to my lab mates Mr. S. Asad Ali and Km. Merma Mishra for their support and help. I remember with great pleasure to my friends Mukesh Babu, Dr. Shalendra Kumar, Dr. Dinesh Singh, Arun Pawar, Dr. Naseem A. Khan, Devendra Kumar, Rupesh Kimiar, Hargyan Singh and Bindesh Kumar Dixit for making my days cheerful and enjoyable and also for encouragement from time to time. I am grateful to University Grant Commission (UGC), Department of Science and Technology (DST), New Delhi. Council of Scientific Industrial Research (C.S.I.R.), New Delhi and Indian National Science academy, (INSA), Chennai for providing financial assistance. None of this would have been possible without the constant support and encouragement of sister, brother and relatives and well-wishers throughout. I am really at the loss of words to express my obligation to my parents who have supported me all through and allowed me to work smoothly. This thesis owes most to them. Lastly, I am in dearth of proper words to express my abounding feelings for my wife, Mrs. Shashi who has been a source of inspiration to me and my sons, Ayush Kumar Singh and Nikhil Kumar Singh for their understanding and cooperation shown. I miss very much my grand father who is no more by my side to share my moment of joy. 1 dedicate this thesis to my beloved family and to the sacred memory of my grand father. (Ajay Kumar Mahur) Contents Chapter I Introduction Page no. 1. General 1 1.1 Radon 3 1.2 Thoron and its progeny 10 1.3 Sources of indoor radon 11 1.3.1 Soil 11 1.3.2 Building materials 11 1.3.3 Water 12 1.3.4 Meteorological Parameters 12 1.4 Radon induced health effects 13 1.4.1 Lung cancer 13 1.5 How Does Radon Get Into Homes? 1.6. Risks of radon exposure at workplaces 19 1.7 Natural Radioactivity 20 1.7.1 Radiation Dose 21 1.7.2 Radiation Protection 22 1.7.3 Health effects due to radioactivity 1.8 Radiation levels and their effects 24 ABBREVIATIONS 28 DEFINITIONS 28 Action level 28 Dose limit 28 Effective dose 28 Equilibrium Equivalent Concentration of radon (EEC radon) 29 Equilibrium Equivalent Concentration of thoron (EEC thoron) 29 Potential Alpha Energy Concentrations (PAEC) 29 Working Level (WL) 30 Working Level Month (WLM) 30 Indoor internal exposure due to radon inhalation 30 Radium equivalent activity (Raeq) 31 Absorbed gamma dose rate (D) 31 External (Hex) and Internal (Hin) Hazard Index 31 References 31 Chapter II Techniques, Materials and Methods 2.1 Radiation Detection 39 2.2. Solid State Nuclear track detectors (SSNTDs) 39 2.3 Track Fonnation Criteria 40 2.4 Radon Measurement Techniques 47 2.5 Instantaneous radon measurement techniques 47 2.5.1 Grab Sampling Technique 47 2.5.2 Ionization Chamber Technique 47 2.5.3 Radon Emanometry 48 2.6 Time integrated long term radon measurement techniques 48 2.6.1 Charcoal Technique 48 2.6.2 Plastic Bag Technique 49 2.6.3 Thermo luminescence Detector Technique 49 2.6.4 Alpha Meter Technique 49 2.6.5 Track Etch Technique 49 2.7 Radon and Thoron measurements using twin chamber dosimeters 54 2.8 Measurement of radon exhalation rate 58 2.9 Natural radioactivity measurements 2.9.1 Gamma-ray spectroscopy technique using Nal (Tl) detector 61 2.9.2 Ganuna-ray spectroscopy technique using HPGe detector 61 2.10 Fission track registration technique 62 References 65 Chapter III Measurement of Indoor Radon, Thoron and Their Progenies in Indian Dwellings and Environment 3.1 Introduction 68 3.2 Radon in workplaces 70 3.3 Action levels limits 70 3.4 Measurement of radon and its progeny Indian dwellings 71 3.5 Materials and methods 71 3.6. Results and discussion 72 3.6.1 Radon levels in dwellings of Palampur and Baijnath (Himachal Pradesh) 72 3.6.2 Radon levels in the dwellings along the South West coast of Kerala High Background Radiation areas (HBRA) 77 3.6.3 Radon levels in some dwellings aroimd Nuclear Atomic Power Plant, Narora, Bulandshahr (Uttar Pradesh) 81 3.6.4 Study of radon and its daughters in dwellings of Bhatinda near a thermal power plant (Punjab), India 87 3.6.5 Indoor radonmonitorin g in some buildings surrounding the National Hydroelectric Power Corporation (NHPC) Project at Upper Siang in Arunachal Pradesh, India 89 3.5.6 Indoor radon monitoring and effective dose measurement in some dwellings of Gujarat 92 3.6.7 Radon monitoring in the dwellings of Jharkhand State India. 95 3.7.1 Indoor radon, thoron and their progeny in some Indian dwellings of U. P., India using twin chamber dosimeter cups with SSNTDs 98 3.7.1 Study of Indoor Radon/Thoron in Some Dwellings Surrounding Narora Atomic Power Station (NAPS) Using Twin Chamber Dosimeter Cups. 104 References 107 Chapter IV Measurement of Natural Radioactivity and Radiation Doses in Solids and Building Construction Materials 4.1 Introduction 110 4.2 Energy savings and environmental benefits 112 4.3 Natural radioactivity and radiation risk measurement in coal and fly ash samples 113 4.3.1 Geology of study areas 114 4.3.2 Experimental 116 4.3.3 Calculation of radiological effects 116 Radium equivalent activity (Raeq) 111 Absorbed gamma dose rate measurement (D) 117 External (Hex) and internal (Hin) hazard index 117 4.3.4 Results and discussion 118 4.3.4.1 Kolaghat thermal power plant 118 4.3.4.2 Durgapur thermal power plant 123 4.3.4.3 Bandel thermal power plant 130 4.4 Natural radioactivity in rock samples 134 4.4.1 Geology ofthe study area 134 4.4.2 Experimental 137 4.4.3 Results and discussion 138 4.5 Natural radioactivity in ^oil samples 143 4.5.1 Experimental 143 4.5.2 Results and discussion 143 4.6 Natural radioactivity in sand samples 4.6.1 Result and discussion 146 4.7 Uranium concentration in building Construction materials using Fission Track Registration technique 153 4.7.1 Experimental 153 4.7.2 Results and discussion 154 4.8 Measurement of effective radium content in sand samples 158 4.8.1 Experimental 158 4.8.2 Theoretical details 160 4.8.3 Results and discussion 162 References 164 CHAPTER -1 i^AT\TTrtr 11 tt^,>v a Chapter-I 1. General Radiation is the signature of nucleus. Radiation is energy traveling through space. Sunshine is one of the most familiar forms of radiation. It delivers light, heat and suntans. We control our exposure to it with sunglasses, shade, hats, clothes and sunscreen. There would be no life on earth without lot of sunlight but we have increasingly recognized that too much of it on our persons is not a good thing. Sunshine consists of radiation in a range of wavelengths from long-wave infra-red to short-wavelength ultraviolet. Beyond ultraviolet are higher energy radiations which are used in medicine and which we all get in low doses from space, from the air and from the earth. Collectively we can refer to these kinds of radiation as ionizing radiation. It can cause damage to matter, particularly living tissues. At high levels it is, therefore, dangerous so it is necessary to control our exposure to radiation. Radiations are of two types: 1. Natural Radiation 2. Man-made Radiation Natural radiations that are exposing the inhabitants can be further divided in two types: (i) Terrestrial radiation (ii) Extraterrestrial radiation Terrestrial radiation is emitted by natural radioactive materials present in earth's crust. These include uranium, thorium and their daughter products radon and thoron. Radiations coming from outer space in the form of cosmic rays are called extraterrestrial radiations. These radiations irradiate human beings internally as well as externally. Exposures from sources outside the body constitute the external exposure and from radionuclides taken inside the body through inhalation or ingestion constitute the internal exposure. Table-1 presents the armual effective doses to adults from natural sources (UNSCEAR, 1993). Table-1 Source • Annual effective dose( mSv) Extraterrestrial radiation Cosmic rays 0.38(16.1%) Cosmogenic radio nuclide 0.01 (0.42%) Terrestrial radiation External exposure 0.46(19.5%) Internal exposure 0.23 ((9.77%) Radon and its progeny Inhalation 1.2(51.0%) Ingestion 0.005 (0.21%) Thoron anc its progeny Inhalation 0.07 (3.0%) It can be observed that radioactive elements form a major source of natural radiation and the natural radioactivity has become a major concern for mankind. Natural radioactivity is wide spread in the earth's environment and it exists in various geological formations in solids, plants, water and air. Uranium is a naturally occurring radioactive element present in trace amounts throughout the earth's crust. Radon is a progeny of uranium decay series formed from radioactive decay of radium in the environment, soil, groundwater, oil and gas deposits and is the primary source of naturally occurring a-radiation present everywhere in the environment in varying concentration. Radon is the heaviest known gas, nine times heavier than air and is the only gas in the long deca> chain of heavy metal elements (Ibrahiem et al.. 1993; Malance et al., 1996; Aly Abdo et al., 1999). Public interest and concern with the radioactivity in the environment is increasing in recent times although the phenomenon of radioactivity was discovered in the starting th of 20 century by Henry Becquerel when he was carrying out experiments connected with X-rays, using uranium salts. Later, investigation on radioactivity was carried out by the Curies using minerals, particularly pitchblende which was many times more radioactive than pure uranium salts. Following this, radioactivity was discovered in several materials, including Potassium, Samarium etc. The fundamental laws concerning radioactivity were also formulated in due course. 1.1 Radon Radon is a gaseous radioactive element having the symbol Rn, the atomic number 86, an atomic weight of 222, a melting point of -71°C. a boiling point of -62°C and depending on the source, there are between 20 and 25 isotopes of radon (20 cited in the chemical summary, 25 listed in the table of isotopes). It is an extremely toxic, colorless and odorless gas. It can be condensed to a transparent liquid and to an opaque, glowing solid. It is derived from the radioactive decay of radium, used in cancer treatment, as a tracer in leak detection and in radiography. It has been identified as a leading cause of lung cancer. Natural Radon, however, consists of three isotopes, one from each of the three natural radioactive disintegration series of uranium, thorium, and actinium (Figures 1-3). The longest lived isotope, '^Rn (alpha emitter of 3.82 da\s half-life), discovered in 1900 by the German chemist Friedrich E. Dom, arises in the uranium series. The name radon is sometimes reserved for this isotope in order to distinguish it from the other two natural isotopes, called 'thoron' and 'actinon' because they originate from the thorium and actinium decay series, respectively. The gas thoron, "'"Rn (alpha emitter of 55.6 second half-life), was first observed in 1899 by the English scientists R B Owens & Ernest Rutherford who noticed that some of the radioactivity of thorium compounds could be blown away. The gas actinon, '''Rn (alpha and gamma emitter of 3.92 second half-life), was found in 1904 independently by Friedrich O. Giesel & Andre-Louis Debierne. to be associated with actinium. Tables -2 and 3 show the decay chain of' "Rn and ^20^" 00 a n > V3 PI m a + •• TKi / " 3 a 2 ~ 00 ^ Figure-1 •IT O U decay series (Adopted from Radiation Safety division Bhabha Atomic Research Centre, Mumbai India) R ^-•^*o ^- ._, id- 1^ 'O ;^ fP •o t-- W fc S^ n o, --^t ^ "3* .-c ^* s? 1^ M ?! a o n--< . ^^ •^a C-. r^ c^ C^ 3 fl •8^ 8 (-CO- W-1 f-- 00 c^ ^ ^^ •O C-- •o — o M & s S':^' - ^ SS 8 fc s? — f^^ '< ^ » -^ ?r a. 2 s- 3u o o S3 ?r J^ 5 <^ s ft s « 3 "v :tx? o o ^ 1 .^1 ^ Cn" S^ cn ^ Q \ « 1 —^ •"• ^^ o o r^ (Ji ^ "^ — 00 Q P- (-- a: ^ CO O -c OJ '' 1 CO O -C m (N -cj- r- —< -^ o "• CQ s gj ,-<. n P. i:*- •« « f- R CO O ^*<^^ ss. • - r ^ ?= s m oq o ^ -^ ^j sS i I tfS r^ .-t ,_(, !S t-4 « 5" _, Sz- '*" ™ c*^ 2- fl- —'t«s^ F. XJ?* tx^ ;^ ^ S * a 2 ez;«|^i o -o a » a 3,15 - ^r Figure-2 232T h decay series (Adopted from Radiation Safety division Bhabha Atomic Research Centre, Mumbai India) ,, ^ a i E 2. ii J S •i ^ ^a. -&r . s © •_ O O 'tn o Ci o •J •^ -^ S '_ -^ « * i- O so i- = -r O K f^f T^* n> -"= C J — >*; 3 V ^> . < «' JmO V5 sr r, 2 I Figure-3 235U decay series (Adopted from Radiation Safety division Bhabha Atomic Research Centre, Mumbai India) Table-2 The decay products of • 22"Rn2 , a gaseous member of the naturalJy occurring 210 206 radioactive series U Pb a-particle Traditional Isotope Half-Life Radiations decay energ>' Name (MeV) Radon ^^^Rn 3.82 davs a 5.45 Radium A ^'«Po 3.05 minutes a 6.00 Radium B ^'H 26.8 min P.Y - Radium C ^'^Bi 19.8 min (3.Y - Radium C '"Po 1 164 ^is a 7.69 ilOpj, Radium D . 22.3 years (3.Y - Radium E ..Ugj 5.01 days P - Radium F ^'Vo 138.4 days a 5.30 Radium G i06pj^ stable 1 Table-3 The decay products of •22"0 Rn, a gaseous member of the naturally occurring 232n radioactive series" "Th 208 Pb a-particle Traditional Isotope Half^Life Radiations decay energy Name (MeV) Thoron ^^^Rn 55.6 s a 6.29 Thorium A ^"'Po 0.15 s a 6.78 Thorium B •^'^Pb 10.64 h P - Thorium C ^'^Bi 60.55 min {p (66.3%) (to 6.1 ^'^Po a (33.7%) to (^"^Tl)] Thorium C ^'^Po 0.3^5 a (to '"'Pb) 8.78 Thorium C 208 J] 3.05 min P (to '"'Pb) - Thorium D ^"«Pb Stable - a = alpha emission, P = beta emission, y = gamma emission In each decay chain the radon isotope resuhs from an alpha emission by radium. Hence one may rigorously infer that radon production is in proportion to the radium present in the earth. Usually. '^^^Rn and ^'^Rn are produced in uranium rich areas whereas ^''^Rn in thorium rich areas. The relative importance of the three radon isotopes increases with their mean lives and relative abundance. ' Rn is the shortest lived and is virtually always produced in much smaller amounts than Rn, since the natural 235y/238y ratio of these ultimate progenitors is 0.00719. Hence ^'^Rn is largely ignored. ^•^°Rn too is short lived relative to "'^Rn and consequently moves a much smaller distance from its source than Rn. In air, for diffusion constant of 0.1 cm's' , the mean distances of diffusive motion are 2.2 m for ''^Rn and 0.029 m for '^°Rn. Hence in circumstances where signals from relatively distant resources or processes in the earth are sought. "^^Rn is by far the dominant nuclide and '^^^Rn provides only uninteresting local background that one wants to exclude during detection. Health hazards of radon and thoron are not primarily due to these isotopes directly but due to their short lived daughters that can be inhaled. Because radon is a noble gas with a life time that is long relative to breathing times, most of it that is inhaled is exhaled again rather than decaying or becoming lodged in the lungs and later decaying. In contrast, the immediate, promptly decaying daughters of ""Rn (^'*Po, "'"Pb, ^'""Bi and ^'•"Po), which are the part of a condensed phase, attach themselves to aerosols and can be inhaled. These daughter products then get deposited on epithelial surfaces within the lung and decay out shortl). When radon decays to form its progeny ("'^Po and "' Po), they are electrically charged and can attach themselves to tiny dust particles, water vapours, oxygen, trace gases in indoor air and other solid surfaces. These daughter products remain air borne for a long time. The dust particles (aerosols) present in the atmosphere can easily be inhaled into the lung and can adhere to the epithelial lining of the lung, thereby irradiating the tissue by a-particles. Bronchial stem cells and secretion cells in airways are considered to be the main target cells for the induction of lung cancer resulting from radon exposure. The radon contributors to the human exposure are shown in Figure - 4. Since the longest lived of the four daughter products, ^'""Pb has a half life of less than 27 minutes, the whole sequence of decay can be completed before the normal clearance processes of the lung. As a resuh the sensitive surfaces of the bronchi are irradiated by the decay products. The most energetic and destructive of these are the heavily ionizing short range alpha particles from the polonium isotopes ^'^Poand^'^o. iEil!!G^^ ^WMIIIIII11 1111 H«Wt\ Z3flu 232TH I I J 4«» Sources |t41|t j^ (building mateiiab, J_ soil, etc.) --'"Ry J Inhalation •deposition in the tract IK".:* \ (large contributioion X tod ose)' Gas (emanation) Particles Particles *, (short-lived (long-lived jBB decay products) decay products 1 \ 1>M f Thoron* P decay products; /' *220Rn Is usually caned thoron -1 ^^ Stable isotope Figure - 4 Radon contributors to human exposure 1.2 Thoron and its progeny Because of its short half life (55 sec) thoron concentrations in a room generally fall off exponentially with distance from its source which is usually internal room surfaces. Due to this, for comparability of thoron measurements it may be necessary for the measurement protocol to include a precise statement on measuring the thoron concentration at some specific distance (x-cm) from the source or as close as practicable to walls and other room surfaces. This latter recommendation has particular relevance to human exposure assessment as during sleep people generally breathe air close to walls. In this situation the lung dose due to the thoron gas itself may even be greater than that from the inhalation of thoron progeny. These may typically be present in the room air at much lower concentrations and will be much more uniformly distributed in the air than the thoron gas itself Since the correlation between thoron gas and its progeny ^'^Pb cannot always be ensured, a correct estimate of the dose may even require measurement of both the gas itself and its progeny. In many investigations, however, the particular scope in mind may only require one type of measurement to be made. Nevertheless, further studies on the spatial and temporal distributions of thoron and its progeny are needed in order to establish reliable protocols for measurements in the interests of comparability of measurement data. For thoron measurements in water, as in the case of radon in water measurements, it is recommended that procedures should be adapted to reduce thoron losses during sampling. 1.3 Sources of indoor radon Main sources of radon in the environment are due to the ambient levels produced by the widespread distribution of uranium and its decay products in the soil. E\ery square mile of source soil, to the depth of six inches, contains approximately one gram radium which releases radon in small amounts to atmosphere (Weast, 1980). The main contributors to the indoor radon levels are as follows: 1.3.1 Soil Soil is the primary source of radon in indoor atmosphere where it is produced by the radioactive decay of radium, found in trace quantities. Soil and rock have concentrations of elements in the uranium and thorium series which vary widely. Estimated average concentrations of uranium and thorium are 25 Bq kg'' each in soil (UNSCEAR, 1986). Radon gas which is chemically inert, then transport through soil and into dwellings through cracks and other openings in the building materials directly. This may be the possible mechanism for the radon transport into the buildings. There are two mechanisms by which radon enters from soil: the first is the movement of radon by molecular difftision through the air pore system in soil, where the soil is assumed to be relatively stationary and the second significant mechanism of entry is the pressure driven flow which is created by forces that drive air infiltration into buildings viz. the thermal stack effect and wind loading on the building shell. Fractures and holes in building foundations as small as 0.5 mm are enough to allow convective migration and gas transport. 1.3.2 Building materials Building materials may be an important source of indoor radon when the radium content of materials is elevated above normal values and emanation rates are very high. Building materials are more easily characterized as indoor radon source than the soil or rocks which constitute building materials. Measurement of emanation rates or ratios for soil and rock performed both in connection with interests in uranium exploration and for the use of radon as an atmospheric tracer, have been reviewed in detail by Tarmer (1987). Ingersoll (1983) has measured the radon emanation rates in a number of building materials. The results of that study indicate that strongest radon emanator is concrete and weakest, the wood. Measurements of the emanation in concrete components revealed that sand is the strongest emanator and cement, the weakest. Within a given type of building material the radon emanation rate varied substantially from one sample to another sample. Even though uranium content of materials might be approximately the same, the radon emanation rates might differ widely, for example granite and rocks used for heat storage have a higher uranium concentration than concrete and yet they exhale radon at lower rates. It was concluded that the physical properties of the various classes of materials account for the wide dispersion of escape to production ratios and thus radon exhalation rate measurements for various materials are very important. 1.3.3 Water Radon can be transferred to the indoor air through the use of water during typical house holds activities like showering, laundering, dishwashing etc. The amount of radon in water at the point of use depends primarily on two factors, i.e., the local geologic character; and type of water supply. The occurrence of radon in water is controlled by the chemical concentration of radium in the host soil or rock and by emissivity of radon into the water. The physical condition of the rock matrix appears to play an important role in radon release into water. Experimental and theoretical considerations indicate that diffusion along micro crystalline imperfections dominates the release of radon into the surrounding water (Hess et al., 1985). Highest levels were observed in drilled wells; especially in granite area and lower concentrations were found in water from dug wells and surface water sources. It is likely that, in normal circumstances, radon escaping from groundwater in the soil does not give rise to higher concentration in buildings. The reason is partly that concentrations in the soil air are normally as high as in groundwater, partly that the water content in the soil horizon immediately above the water table is so great that diffusion through the soil is prevented. Only if the radon concentration in the groundwater is much higher than that in the soil gas, and if the groundwater is in motion or flows out at the surfaces, it is likely that sufficient radon will be released to affect its concentration in the building. 1.3.4 Meterological Parameters Varying environmental conditions have been found to affect the rate of radon emanation. Jonassen and Mclaughlin (1977) found pressure dependence for long term emanation rates from concrete walls. However, IngersoU (1981) did not observe any detectable increase in emanation rate with a pressure drop down to 20 inches of mercury 12 for 2 to 3 days. Similarly the effect of temperature is uncertain. Stranden et al., (1984) measured increased radon exhalation from concrete samples with increase in temperature. However, Auxier et al., (1973) found that within the normal range of home temperature, the temperature of the concrete is not a sensitive parameter and has negligible effects on the emanation rate. Moisture has been found to have significant effect on the radon emanation rate. Auxier et al, (1973) reported that if moisture increases from the normal 2-4% by weight to 6-8 % by weight, the emanation rate may increase by 10-20%. Ingersoll (1981) found an even greater effect. By increasing the moisture of the concrete sample by 4% (weight) there was an increase in radon emanation of about 100%. 1.4 Radon induced health effects The exposure to radon and its progeny can give rise to many health related malignancies. While the association of radon to lung cancer is well known, several studies have related radon to risk of leukemia, melanoma, cancer of kidney and prostate. A brief introduction of various health effects of radon is being given here. 1.4.1 Lung cancer Radon is the second leading cause of lung cancer (Sevc et al., 1976). The main epidemiological evidence for role of radon in causing lung cancer comes from the various studies on miners in different countries. Some of the results of these studies are summarized in Table 4&5. Most of these studies consistently show an increased risk of lung cancer of miners. Though it is believed that in some of these studies, elements other than radon and thoron, such as arsenic and silica dust present in mine atmosphere might have influenced the results. But in other cases where radon and progeny exposure has been low, little or no excess of lung cancer has been observed. Therefore, taking these studies together, the role of radon as a cause of lung cancer in miners is well supported by epidemiological observations. As regards the indoor radon exposure and lung cancer risk for general population, several studies have been carried out since 1979. Most of these studies have been of case-control type. Results of these studies are given in Table-6 and 13 most of these suggest the effect of radon regarding the lung cancer. Svensson et ai., (1987) clearly established the association of oat-cell cancers in women with indoor radon. Another study (Damber and Larsson 1987) also established predominance of squamous and small cell carcinomas in people living in non- wooden houses than those living in wooden houses. A recent nation wide- control study has been reported from Sweden (Pershagen et al., 1984). Radon and its progeny were regarded as radiation health hazards encountered only in the mining and processing of uranium ores. This notion has changed markedly as a resuh of increasing efforts made in many States to measure radon in dwellings, mines other than uranium mines and workplaces suspected of having high atmospheric radon levels. In temperate and cold regions, energy conservation measures have been taken in buildings that have resulted in reduced ventilation rates and increased radon concentrations, particularly in winter months. This rise in the indoor air concentration of radon was recognized as a radiation health hazard, potentially causing an increase in the incidence of lung cancer. Radon thus became a concern not only in underground mines but also in buildings in areas with elevated levels of radon in soil gas or in buildings constructed with materials containing significant levels of radium. According to an assessment by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR. 2000) environmental radon accounts for half the human exposure to radiation from natural sources. 14 Table-4 Main results of some cohort studies of lung cancer in miners exposed to radon and progeny (adopted from Axelson, 1995) Type of Exposure or Person- Lung Cancer deaths Observed Mining, concentration Reference years Expected SMR Country mean values Metal, 0.05-0.40 WL 23862 47 16.1 2.92 Wagoner et al., U.S.A. 1963 Waxweiler et al., 1981 Uranium, 821 WLM 62556 185 38.4 4.82 Lundin et al., U.S.A 1971 Placekei al., 1983 Uranium 289 WLM 56955 211 42.7 4.96 Kunz et al., Czecho 1978 slovakia Tin, U.K. Tin. U.K. 1.2-3.4 WL 27631 28 13.27 2.11 Foxetal.. 1981 Iron 0.5 WL 10230 28 6.79 4.12 Jorgesen, 1984 Sweden Iron 81.4 WL 24083 50 12.8 3.90 Radford & Renard, 1984 Sweden Fluorspar, Up to 2040 37730 104 24.38 4.27 Morrision et Canada WLM al., 1988 Uranium 40-90 WLM 202795 82 56.9 1.44 MuUeretal.. Canada 1985 Uranium 17 WLM 118341 65 34.24 1.90 Howe et al., Canada 1986 Iron, U.K. 0.02-3.2 WL 17156 39 25.50 1.53 Kinlen & Willows, 1988 Pyrite 0.12-0.36 WL 29577 47 1.1 12.70 Battista et al., Italy 1988. Uranium- 720 WLM 7861 14 1.1 12.70 Roscoe et al., Non 1989 smokerss U.S.A. Tin, U.K. lOWLM/year - 15 3.4 447 Hodgson & for 30 years Jones, 1990 Tin, 2.3-0.9 WL by 175143 981 - Up to 1.8 Xiang-Zhen et China time al., 1993 15 Table-5 Main results of some case -control studies of lung cancer in miners exposed to radon and progeny (adopted from Axelson, 1995) Type of Exposure or Number of Number of Rate ratio, Reference mining concentratio cases to exposed max n mean control cases Ratio values Zinac- Lead, 1 WL 29/174 21 16.4 Axelson & Sweden Sundell, 1978 Iron, Sweden 0.1-0.2 WL 604/(467 X 20 7.3 Damber & 2+137) Larsson, 1982 Iron, Sweden 0.3-1.0 WL 38/403 33 11.5 Edling & Axelson, 1983 Uranium 30-2, 698 32/64 23 Infinite Samet et al.. U.S.A. WLM 1984 l^ranium 472 WLM in 65/230 All 1.5% WLM Samet et al.. U.S.A. cases (Nested) 1989 Tin, China 515 WLM in 107/101 7 20.0 Qiaetal.. cases 1989 Tin, China 373 WLM 74/74 5 (13.2)1.7% Lubin et al., per WLM 1990 Table-6 Main results of some case -control studies of lung cancer in miners exposed to radon and progeny (adopted from Axelson, 1995) References Number of cases to Rate ratio Remarks control Axelson, et al., 1979 37/178 1.8 Significant trend ; crude exposure assessment Lanes et al., 1982 50/50 2.1 Published abstract only Edlingetal., 1984 23/303 Up to 4.3 Special account for geology and radon emanation Pershagen et al., Two sets of 30/30 Significantly high 1984 exposure for smoking cases Damber & Larsson, 604/(467x2 + 137) Up to 2.0 For more than 20 1987 years non-wooden houses Svensson et al., 292/584 2.2 Women with Oat 1987 cell cancer Leesetal., 1987 27/49 . Up to 11.9 Risk of 11.9 for 10 WLM Axelson, et al., 1988 177/673 Upto 2.0 Clear effect for rural residents only Svensson et al., 210/209 Up to 1.8 (in middle Females; rare ratio 1989 +191 (Hospital) exp. Category) 3.1 for small cell cancers Schoenberg et al., 433/402 Up to 1.7 Females in high risk 1989 (small cell) area (China), slight effect for small- cell cancers only Blotetal., 1990 308/356 Up to 7.2 Females; little effect but in higher exposure category Ruosteenoja, 1991 238/434 Up 0 1.9 Lower effect at the highesty exposure Pershagen et al., 210/209+191 1.7 as average Rate ratio upto 21.7 1992 (Hospetal) for smokers and high exposure 17 1.5 How Does Radon Get Into Homes? Radon is a radioactive gas. It comes from the natural decay of uranium that is found in nearly all soils. It typically moves up through the ground to the air above and into the home through cracks and other holes in the foundation. Home traps radon inside where it can build up. Any home may have a radon problem. This means new and old homes, well-sealed and drafty homes and homes with or without basements. Radon from soil gas is the main cause of radon problems. Sometimes radon enters the home through well water. In a small number of homes, the building materials can give off radon too. However, building materials rarely cause radon problems by themselves. Radon gets in through; 1. Cracks in solid floors 2. Construction j oints 3. Cracks in walls 4. Gaps in suspended floors 5. Gaps aroimd service pipes 6. Cavities inside walls 7. The water supply 18 1.6. Risks of radon exposure at workplaces Since radon is a gas, it may escape into the air from the material in which it is formed and since uranium and radium occur widely in soil, rocks and water, radon gas is ubiquitous outdoors as well as indoors, the air that we inhale contains radon. Radon decays to a number of short lived decay products ('progeny') that are themselves radioactive. These may attach to available aerosol particles in the atmosphere, thereby forming what are termed 'attached' radon progeny whose size will reflect the size distribution of the ambient aerosol. Those radon progeny that do not attach to aerosols remain in what is termed the 'unattached' state, and these unattached particles are usually found to be in the approximate size range of 0.5-5 rmi. If inhaled, both unattached and attached radon progeny may deposit in the lungs and irradiate lung tissue as they decay. In lung dosimetry models in which deposition sites of radioactive material and locations of target cells are taken into account, the risk per unit of inhaled radioactive material is considered to be much greater for radioactive material in the unattached state than for radioactive material in the.attached state (NRC, 1988). While it is the radon progeny rather than radon gas itself that presents the greater risk, the word 'radon' is also used generally as a convenient shorthand for both the gas and its progeny. Radon has been recognized as a radiation hazard causing excess lung cancer among underground miners (ICRP, 1981). Consequently radon has been classified as a human carcinogen. Since the 1970s evidence has been increasing that radon can also represent a health hazard in non-mining environments (ICRP, 1993). Since environmental radon on average accounts for about half of all human exposure to radiation from natural sources (UNSCEAR, 2000), increasing attention has been paid to exposure to radon and its associated health risks in both industrialized and developing countries. One particularly important factor is the radioactive equilibrium between radon and its progeny. This is expressed as the ratio of the total alpha particle energy that the particular mixture of radon and its progeny will emit to the total energy emitted by the same concentration of radon gas in perfect equilibrium with its progeny. For most indoor envirormients of interest, the state of equilibrium between radon and its progeny is fairly constant, and this ratio is usually taken to be 40-50%. Howexer, depending on conditions (especially 19 ventilation conditions), some workplaces may exhibit values of this ratio down to 20% or up to 80%. For these more extreme cases it may be desirable to modify some of the information in this report relating to radon concentrations. Much of the discussion in the scientific literature on indoor radon is expressed in terms of radon concentrations rather than concentrations of radon decay products, for two principal reasons. Firstly it is much easier to measure concentrations of radon gas than concentrations of its progeny, especially for long term measurements. The second reason is that, owing to the higher dose conversion factor of the unattached fraction of radon progeny in lung dosimetry models and the inverse relationship between the unattached fraction and the equilibrium factor in indoor air, the effective dose relates. 1.7 Natural Radioactivity Radioactive decay is spontaneous phenomenon of emission of particles or electromagnetic radiation from an atomic nucleus. Thermodynamic instability of a nucleus is responsible for the spontaneous decay so as to obtain more stable nucleus. Nuclear decay is accompanied by emission of alpha, beta, gamma, neutron, proton and even heavier elements (isotopes). Radioactivity is a part of our earth and it has existed all along. Naturally Occurring Radioactive Materials (NORM) are present in its crust, the floors and walls of our homes, schools or offices and in the food .There are radioactive gases in the air we breathe. Our own body muscles, bones, and tissues contain naturally occurring radioactive elements. Radioactivity is the term used to describe disintegration of atoms. The atom can be characterized by the number of protons in the nucleus. Some natural elements are unstable. Therefore, their nuclei disintegrate or decay, thus releasing energy in the form of radiation. This physical phenomenon is called radioactivity and the radioactive atoms are called nuclei. The radioactive decay is expressed in units called Becquerel. One Becquerel equals one disintegration per second. The radionuclides decay at a characteristic rate that remains constant regardless of external influence, such as temperature or pressure. Half life differs for each radionuclide, ranging from fractions of a second to billions of years. For example, the half life of Iodine- 131 is eight days, but for Uranium 238, which is present in 20 varying amounts all over the world, it is 4.5 billion years. Potassium 40, the main source of radioactivity in our bodies has a half life of 1.42 billion years. Natural radioactivity is wide spread in the earth's environment coming from Uranium ("*U) and Thorium (^^^Th) series and Potassium ("""K), existing in various geological formations like soils, rocks, plants, water and air (Beretka and Mathew, 1985; EC, 1999; Singh et al., 1999; Kumar et al., 2003; Anjos et al., 2005; Ahmed et al., 2006). Radiological implication of these radionuclides is due to the gamma ray exposure of the body and a- irradiation of lung tissues from inhalation of radon and its daughters. The assessment of gamma radiation dose and radon exhalation rate from natural sources is of particular interest as natural radiation is the largest contributor to external dose of the world population (UNSCEAR, 1993; El-Arabi, 2007). As uranium can get dissolved in aqueous solutions in hexavalent (U^"^) form and can be precipitated as a discrete mineral in tetravalent (U'*") form. Uranium may form deposits in the earth's crust where the geological conditions become favorable. Under specific conditions such as those prevailing in the uranium mining environment lung dose due to radon progenies may be sufficiently high. Growing world wide interest in natural radiation has lead to extensive suH'eys in man}' countries. External gamma dose estimation due to terrestrial sources is essential not only due to its considerable contribution (0.46 mSv y"') to collective dose but also because of the variations of individual doses related to its path ways. These doses vary depending upon the concentrations of the natural radionuclides ^^^U and ^^^Th and their daughter products and ''°K, present in the soils and rocks which in turn depend upon the local geology and region in the world (Radhakrishna et al., 1993; Rudnic Gao, 2003). 1.7.1 Radiation Dose Ionizing radiation can impair the normal functioning of the cells or even kill them. The amount of energy necessary to cause significant biological effects through ionization is so small that our bodies can not feel this energy as in the case of infra-red rays which produce heat. The biological effects of ionizing radiation vary with the type and energy. A measure of the risk of biological harm is the dose of radiation that the tissues receive. The unit of absorbed radiation dose is Sievert (Sv). Since one sievert is a large quantity, radiation doses normally encountered are expressed in milli Sievert (rhSv) or micro Sievert 21 (jiSv) which is one-thousand or one milHonth of a Sievert. For example, one chest X-ray will give about 0.2 mSv of radiation dose. On the average, our radiation exposure due to all natural sources amounts to about 2.4 |aSv a year, though this figure can vary, depending on the geographical location by several hundred percent. In homes and buildings there are radioactive elements in the air. These radioactive elements are ^^^Rn (radon) and ^^°Rn (thoron) and by products formed by the decay of radium and thorium present in many sorts of rocks, other building construction materials and in soil. By far the largest source of natural radiation exposure comes from varying amounts of uranium and thorium in the soil around the world. The radiation exposure due to cosmic rays is very dependent on altitude and slightly on latitude: people, who travel by air thereby, increase their exposure to radiation. Additionally, we are exposed to varying amounts of radiation from sources such as dental and other medical X- rays, industrial uses of nuclear techniques and other consumer products such as luminized wrist watches, ionization smoke detectors etc. We are also exposed to radiation from radioactive elements contained in fallout from nuclear explosives testing and routine normal discharges from nuclear and coal power stations. 1.7.2 Radiation Protection It has long been recognized that large doses of ionizing radiation can damage human tissues. Over the years, as more was learned, scientists became increasingly concerned about the potentially damaging effects of exposure to large doses of radiation. The need to regulate exposure to radiation prompted the formation of number of expert bodies to consider what is needed to be done. In 1928, an independent non-governmental body of experts in the field, the International X-ray and Radium Protection Committee was established. It later was renamed as the International Commission on Radiological Protection (ICRP). Its purpose is to establish basic principles and issue recommendations on radiation protection. These principles and recommendations form the basis for national regulations governing the exposure of radiation workers and members of the public. They also have been incorporated by the International Atomic Energy Agency (IAEA) into its Basic Safety Standards for Radiation Protection published jointly with the World Health Organization 22 (WHO), International Labour Organization (ILO), OECD and Nuclear Energy Agency (NEA). These standards are used world wide to ensure safety and radiation protection of radiation workers and the general public. An intergovernmental body was formed in 1955 by the General Assembly of the United Nations as the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). UNSCEAR is directed to assemble study and disseminate information on observed levels of ionizing radiations and radioactivity (natural and man-made) in the environment and on the effects of such radiation on man and environment. Basic approaches to radiation protection are consistent all over the world. ICRP recommends that any exposure above the natural background radiation should be kept as low as reasonably achievable, but below the individual dose limits. The individual dose limit for radiation workers averaged over 5 years is 100 mSv and for the members of the general public is ImSv per year. These dose limits have been established based on a prudent approach by assuming that there is no threshold dose below which there would be no effect. It means that any additional dose will cause a proportional increase in the chance of a health effect. This relationship has yet been established in the few low dose range where the dose limits have been set. There are many high natural background radiation areas around the world where the annual radiation dose received by rriembers of the general public is several times higher . than the ICRP dose limit for radiation workers. The numbers of people exposed are too small to expect to detect any increase in health effects epidemiologically. Still the fact that there is no evidence so far any increase does not mean the risk is being totally disregarded. The ICRP and the IAEA recommend that consideration must be given to the presence of other sources which may cause simultaneous radiation exposure to the same group of the public. Also, allowance for future sources or practices must be kept in mind so that the total dose received by an individual member of the public does not exceed the dose limit. In general, the average annual dose received by radiation workers is found to be considerably lower than the individual dose limits. Good radiation protection practice can thus result in low radiation exposure to workers. 23 1.7.3 Health effects due to radioactivity Generally assumed that any resulting health detriment (e.g. cancer, cellular damage etc.) is brought about by exposure to a radioactive substance and is primarily a function of the amount of energy (as ionizing radiation) absorbed per unit mass of tissue through which it passes. Ionizing radiation emitted by different radionuclides differ in their ability to penetrate matter depending both on the type of radiation emitted and its energy. Alpha particles are hardly able to penetrate the outer layer of skin and do not constitute a hazard when emitted outside the body. Beta particles are able to penetrate the outer layers of skin and can give rise to localized dose to the skin when in contact. Gamma radiations is potentially more penetrating and can deposit energy to internal organs when outside the body , the magnitude of which depends on the energy of gamma radiation emitted. Thus exposures from radionuclides may be both extemal and internal to the body and the relative importance of these exposures pathways depends upon the type of radiation and the radionuclides involved. Two types of health effect have been shown to result from exposure to ionizing radiation, deterministic and stochastic effects. Deterministic effects are those that occur at high doses and dose rates. These effects occur at dose levels far higher than those encountered from the use of exposure to radioactive materials under normal envirormiental conditions and exposures to general public. Erythema or reddening of the skin is a form of deterministic effect that may result from skin exposure (at instantaneous absorbed dose of 5Gy or more). Above the dose threshold the likely severity of such effects is affected by the dose received. The primary stochastic effect associated with radiation exposure is cancer induction. Most of the information relating radiation doses to an increased risk of cancer is derived from situation in which people have been exposed at higher doses and dose rates than normally encountered ( e.g. Nagasaki and Hiroshima bomb survivors). At lower levels of dose and dose rate, it is difficult to demonstrate an increased cancer incidence from radiation exposure because of the high natural incidence of cancer, which is a major confounding factor in the epidemiological studies, particularly at low doses and dose rates. Information about the way in which radiation-interacts with cells, however, supports what has become known as the linear no- threshold hypothesis. Uranium nuclides emit alpha rays of high ionization power and therefore, it may be hazardous if inhaled or ingested in higher quantity or dose. Uranium a 24 primordial radionuclide occurs in dispersed state in the earth,s crust. Uranium prospection through the analysis of soil, rocks, plants and water has been reported by many workers (Dyck, 1979; Dunn, 1981). Uranium present in the earth is transferred to water, plants, food supplements and then to human beings. Uranium accumulated in humans may have dual effect due to its chemical and radioactive properties. High intake of uranium ad its decay products may lead to harmftil effects in human beings. According to an estimate (Cothem and Lappenbush, 1983) food contributes about 15% of ingested uranium while drinking water contributes about 85%. An exposure of about 0.1 mg/kg of body weight of soluble natural uranium results in transient chemical damage to the kidneys (Lussenhop et al., 1958). 1.8 Radiation levels and their effects The following points give an indication of the likely effects of a range of whole body radiation doses and dose rates to individuals: • 10,000 mSv (10 sieverts) as a short-term and whole-body dose would cause immediate illness, such as nausea and decreased white blood cell count, and subsequent death within a few weeks. Between 2 and 10 sieverts in a short-term dose would cause severe radiation sickness with increasing likelihood that this would be fatal. • 1000 mSv (Isievert) in a short term dose is about the threshold for causing immediate radiation sickness in a person of average physical attributes, but would be unlikely to cause death. Above 1000 mSv, severity of illness increases with dose. If doses greater than 1000 mSv occur over a long period they are less likely to have early health effects but they create a definite risk that cancer will develop many years later. • Above about 100 mSv, the probability of cancer (rather than the severity of illness) increases with dose. The estimated risk of fatal cancer is 5 of every 100 persons exposed to a dose of 1000 mSv (ie. if the normal incidence of fatal cancer were 25%, this dose would increase it to 30%). 25 • 50 mSv is, conservatively, the lowest dose at which there is any evidence of cancer being caused in adults. It is also the highest dose which is allowed by regulation in any one year of occupational exposure. Dose rates greater than 50 mSv yr'' arise from natural background levels in several parts of the world but do not cause any discernible harm to local populations. • 20 mSv y"' averaged over 5 years is the limit for radiological personnel such as employees in the nuclear industry, uranium or mineral sands miners and hospital workers (who are all closely monitored). • 10 mSv y'* is the maximum actual dose rate received by any Australian uranium miner. • 3-5 mSv y"' is the typical dose rate (above background) received by uranium miners in Australia and Canada. • 3 mSv y"' (approx) is the typical background radiation from natural sources in North America, including an average of almost 2 mSv y"' from radon in air. • 2 mSv y"' (approx) is the typical background radiation from natural sources, including an average of 0.7 mSv/yr from radon in air. This is close to the minimum dose received by all humans anywhere on Earth. • 0.3-0.6 mSv y'' is a typical range of dose rates from artificial sources of radiation, mostly medical. • 0.05 mSv y"', a very small fraction of natural background radiation, is the design target for maximum radiation at the perimeter fence of a nuclear electricity generating station. In practice the actual dose is less. 26 TABLE -7 Conversion Factors SI Unit Traditional Unit Conversion Activity (Bq) 1 Ci = 3.7xI0'° Bq (1 pCi = 0.037 Bq) Concentration (Bq/m^) 1 pCi/liter = 37Bq/m^ Potential alpha energy 1 WL* = 1.3x 10^ MeV/liter = 2.08x10'^ J/m^ conc.(PAEC)) •1 Exposure (J/m s) 1 WLM-12.97 JWS Exposure (Bq/m^ y) 1 WLM = 74.0 Bq/m^ year (for ^^Rn series) Exposure rate 1 WLM/year-4.11 x 10'^ JW Exposure rate 1 WLM/year= 74.0 Bq/m^ (for "^^Rn series) 1 WL = 200 pCi/ liter ( 50% Equil.) 27 ABBREVIATIONS ICRP (International Commission on Radiological Protection) IAEA (International Atomic Energy Agency) lARP (Indian Association for Radiation Protection) BEIR (Biological effects of Ionizing Radiation) UNSCAER (United Nations Scientific Committee on the Effects of Atomic Radiation) DEFINITIONS Action level The level of dose rate or activity concentration above which remedial actions or protective actions should be carried out in chronic exposure or emergency exposure sittiations (for example, chronic exposure to radon in the workplace). Dose limit The value of the effective dose or the equivalent dose to individuals from controlled practices that shall not be exceeded. Effective dose To estimate armual effective doses, account must be taken of (a) the conversion coefficient from absorbed dose in air to effective dose and (b) the indoor occupancy factor. The average numerical values of those parameters vary with the age of the population and the climate at the location considered. In the UNSCEAR 1993 Report, the Committee used 0.7 Sv Gy'' for the conversion coefficient from absorbed dose in air to effective dose received by adults and 0.8 for the indoor occupancy factor, i.e. the fraction of time spent indoors and outdoors is 0.8 and 0.2, respectively. These values are retained in the present analysis. The components of the annual effective dose are determined as follows: Indoors: 84 nGy h"' x 8,760 h x 0.8 x 0.7 Sv Gy'' = 0.41 mSv Outdoors: 59 nGy h"' x 8,760 h x 0.2 x 0.7 Sv Gy'' = 0.07 mSv 28 The unit of effective dose is J-kg~', termed the sievert (Sv). Effective dose is a measure of dose designed to reflect the amoimt of radiation detriment likely to result from the dose. Equilibrium Equivalent Concentration of radon (EEC radon): The potential alpha energy concentration (PAEC) of any mixture of radon progeny in air can be expressed in terms of the so-called equilibrium equivalent concentration of their parent nuclide, ^^Rn (radon). The equilibrium equivalent concentration, corresponding to a non-equilibrium mixture of radon progeny in air, is the activity concentration of radon in radioactive equilibrium with its short lived progeny that has the same potential alpha energy concentration as the actual non-equilibrium mixture. The SI unit of the equilibrium equivalent concentration is Bq m'^: EEC radon = 0.104 C (^'^Po) + 0.514 C (^'^Pb) + 0.382 C (^"'Bi) with C ( ) the concentration of the nuclide in air. 1 Bq m"'' EEC radon corresponds to 5.56x10"^ mJ m'\ Also 1 Bqm'^ EEC radon is equivalent to 2.5 Bq m'^ radon gas, assuming an equilibrium factor of 0.4. Equilibrium Equivalent Concentration of thoron (EEC thoron) The equilibrium equivalent concentration, corresponding to a non-equilibrium mixture of thoron progen> in air, is the activity concentration of thoron in radioactive equilibrium with its short lived progeny that has the same potential alpha energy concentration as the actual non-equilibrium mixture. The SI unit of the equilibrium equivalent concentration is Bq m"^: EEC thoron = 0.913 C (^'^Pb) + 0.087 C(^'^Bi) where C() is the concentration of the nuclide in air. 1 Bq m'^ EEC thoron corresponds to 7.5 X 10-5 mJm"l Potential Alpha Energy Concentrations (PAEC) PAEC is the total a- energy emitted by an atom as it decays through its entire radioactive series. The Potential alpha concentration is the sum of all PAE in a given volume of air divided by the volume of air. Conventional unit used is MeVL''.The other unit is J m"". Widely used unit for describing PAEC is Working Level (WL). 29 Working Level (WL) The WL unit was developed for use in radon occupational exposure assessment since often there was incomplete information on the degree of equilibrium with daughter products. WL is the combination of radon progeny such that total potential alpha energy released on ultimate decay to ^'°Pb is 1.28 xio^ MeVL'' (rounded to 1.3 x 10^). For conversion purposes, 1 WL = 1.3x10^ MeV L'' = 2 .08 x 10^ J m'-*. 1 WL corresponds to an activity concentration of 3700 Bq m'^ of ^^^Rn. It is the dose delivered in one liter of air that results in the emission of 1.3 x 10^ MeV of potential alpha energy. Working Level Month (WLM): Although WL was originally defined only for progeny of radon, it can also be calculated for ^^°Rn and ^"Rn by letting IWL equal to L3xl0^ MeVL'' for air regardless of source. IWL corresponds to 275 Bq m'' for ^^°Rn and 5960 Bq m'^ for "''^Rn. The working level is the measure of exposure rate. The exposure of an individual to radon progeny is time integral of PAEC and expressed as Working Level Month (WLM). 1 WLM corresponds to exposure at 1 WL concentration for a period of one month (170 hrs). It is a measure of exposure rather than dose. Since the equilibrium between the parent radon isotope and progeny is rarely achieved due to plate out and ventilation. Indoor internal exposure due to radon inhalation The risk of lung cancer from domestic exposure of ^^^Rn and its daughters can be estimated directly from the indoor inhalation exposure (radon)-effective dose. The contribution of indoor radon concentration from the samples can be calculated from the expression (Nazaroff and Nero. 1988): '" ~ VxX Where Can, Ex, S, V and Xy are radon concentration (Bq m'^), radon exhalation rate (Bq m'" h"')h-'). radon exhalation area ( m^), room volume (m'') and air exchange rate (h'' respectively. 30 Radium equivalent activity (Raeq) Exposure to radiation is defined in terms of radium equivalent activity ( Raeq) in Bq kg" to compare the specific activity of materials containing different amounts of U ( Ra). ^^^Th and '^^K. It is calculated through the following expression: Ra eq= Cu + 1.43 Cih + 0.07CK Where Cu, Cih and CKare the activity concentrations of "^U, ^^Th and '^"K in Bq kg"' respectively. Absorbed gamma dose rate (D) The absorbed gamma dose rates (D) in air at Im above the ground surface for the uniform distribution of radio nuclides ('"'"Th. ^''^U & '^^K) are calculated on the basis of guidelines given by UNSCEAR, (2000). The dose conversion factors for converting the activity concentrations of U, Th and K into doses (nGy h per Bq kg') are 0.462, 0.604 and 0.0417 respectively. Thus D = (0.462 Cu + 0.604 di, +0.0417 CK) nGy h'' External (Hex) and Internal ( Hjn) Hazard Index The external hazard index is obtained from Raeq expression through the supposition that its allowed maximum value (equal to unity) corresponds to the upper limit of Raeq (370 Bq kg''). For limiting the radiation dose from building materials in Germany to 1.5 mGy y'' Krieger (1981) proposed the following relation for Hex: c c c 370 259 4810 This criterion considers only the external exposure risk due to y-rays and corresponds to maximum Raeq of 370 Bq kg"' for the material. These very conservative assumptions were later corrected and the maximum permission concentrations were increased by a factor of 2 (Keller and Muth, 1990) which gives C C C " 740Bqkg'' SlOBqkg-' 9620Bqkg'' ~ Internal exposure to ^^^Rn and its radioactive progeny is controlled by the internal hazard index (H,n) as given below (Gotten, 1990): '" 185 259 4810 31 References Ahmed, N.K., Abbady, A., El Arabi, A.M. Michel, R., El- Kamel, A. H., Abbady, A.G., 2006.Comparative study on the natural radioactivity of some selected rocks from Egypt and Germany. Indian J. Pure Appl. Phys. 44, 209-215. Aly Abdo, A. A., Hassan, M.H., Kuwait, M. R. A., 1999. Radioactivity assessment of fabricated phosphogypsum mixtures. Fourth Radiation Physics Conference, Alexandria, Egypt. Anjos, R., Veiga, R., Soares, T., Santos, A., Aguiar, J., Frascac, M.. Brage, J., Uzeda, D., Mangia, L., Facure, A., Mosquera, B., Carvalho, C Gomes. P.. 2005. Natural radionuclide distribution in Brazilian commercial granites. 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A cohort study in southern China of tin miners exposed to radon and radon decay products. Health Phys. 64, 120-131. UNSCEAR, 1986. Sources and effects of ionizing radiation. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, NewYork. UNSCEAR, 1993. United Nations Scientific Committee on the Effects of Atomic Radiation. Source and Effects of Ionizing Radiation. United Nations, New York. UNSCEAR, 2000. Sources and effects of ionizing radiation. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, New York. 38 CHAPTER -2 liOIIlL Chapter-II 2.1 Radiation Detection Detector is the device which senses the interactions of radiations and converts the interaction to measurable signal. Radiation detection techniques are based on measurement of the charge produced due to interaction of radiation as it passes through detector volume. The net result of the radiation interaction is the appearance of an electric charge within the active volume of the detector (Evans, 1978). The interaction times are so short (Friedlander et al., 1981) that the deposition of radiation energy can be considered as instantaneous and charge appears in the detector at zero time. This charge which is the basic signal for radiation detection must be collected. Charge is collected by applying an electric field across the detector. Time required for charge collection greatly varies from one detector to another depending on the mobility of charge carriers in the detector and the average distance to be traveled. 2.2. SoKd State Nuclear track detectors (SSNTDs) Solid State Nuclear track detectors (SSNTDs) have been employed for recording the charged particle tracks. These detectors have been used for long time for radon, thoron and radon exhalation rate measurements. When energetic charged particles pass through a dielectric medium, they leave a trail of damaged molecules along its track. This is similar to the track recorded by charged particles in nuclear emulsions. Inorganic insulators like quartz, mica, glasses and zircon as well as organic polymers like Lexan, CR-39 and LR-115 type II are widely used as Solid State Nuclear Track Detectors (SSNTDs). Initial track produced by radiation is very small (a few rmi) and can be seen only under an electron microscope. However, etching the detector in alkali or acid tracks can be developed on etching the damaged tracks are preferentially etched out to form small (10-20|im) pits that can be easily seen and counted under a microscope. The sizes of the pits made by alpha particles are substantially small as compared to the pits made by fission fragments. These SSNTDs are insensitive to fast electrons, gamma rays and 39 even protons. Visible tracks in different materials can only be produced if the specific energy loss (-dE/dx) is above the minimum threshold value for that material. 2.3 Track Formation Criteria When a heavily ionizing nuclear charged particle passes through an insulating solid, the physical, chemical and other properties of the solid along and around the path of the particle change and a narrow path of intense damage is created. This narrow path is called latent track and the track recording materials are known as solid state nuclear track detectors. Various authors have suggested to relate the track formation with different parameters, such as total rate of energy loss, primary ionization, restricted energy loss etc. The experimentally set up track formation criterion is that there exists a certain value of energy loss rate known as critical value of energy loss rate below which the tracks are not formed in solids. The critical energy loss is generally denoted by Jc = (dE/dx)c, The values of which is different for different solids but same in a given solid for all the particles as shown in Figure-1. It can be seen from this figure that particle may not be able to produce track if either energy is too low or too high. However if the value of J is less than Jc for a given solid, the tracks will not be formed in the solid at any energy of the traversing particle. The charged particle latent tracks are narrow (< 50A radius) and stable chemically reactive centers of strain, composed mainly of displaced atoms rather than electrons (Maurette, 1970; Fleischer et al., 1975). 40 ENERGY/NUCLEON(MeV) 5 7- 10 0.1 0,5 3 5 7 10 T—r VELOCITY, P=v/c Figure-1: Curves of primary ionization rate as a fiinctiono f relative velocity (P) and energy per nucleon for a number of ions. The experimental points for accelerator ions in lexon polycarbonate are given as open circles for zero registration and as filledcircle s for 100% registration. Thresholds for other detectors are also indicated. 41 On the basis of experimental tests conducted (i) on the measurement of effects of electron irradiation on chemical dissolution rates of solids and (ii) on the measurement of radial distribution of etchable damage in solids, it has been concluded that two separate mechanisms of track formation exist, one for the inorganic solids and glasses and the other for organic solids or polymers. In case of inorganic solids and glasses, the ion explosion spike model proposed by Fleischer et al., (1965) provides a considerably satisfactory explanation of track formation mechanism. According to this model, a positively charged particle knocks out the orbital electrons of the atom lying in and around the vicinity of its path, thus producing the cylindrical region full of positive ions. These positive ions there upon repel one another violently, thus disturbing and distorting the regular lattice in a crystalline solid (Figure-2) and producing a more or less cylindrical region (Bonfiglioli et al., 1961; Lindhard and Thomson, 1962; Chadderton and Montagu Pollock, 1963; Benton, 1967; Fleischer et al., 1967). On the other hand, in case of organic polymers and plastics it is believed that both the primary and secondary ionization and excitation play an important role in the production of etchable tracks in the organic polymers. These broken molecular chains rarely unite at the same place, instead they produce broken bonds and free radicals etc. which are chemically more reactive as shown in Figure-3. These latent damage track trails can be developed by using the appropriate etchant and can be visualized then under the optical microscope. It is explained as follows: as the damage trails are chemically more reactive regions (compared to the undamaged area), on increasing the sample in appropriate etchant, all those trails which intersect the surface are rapidly dissolved and hollow cylindrical tubes about 50 A diameter are left behind. The undamaged well of hollow tube is attacked and its diameter increases into micron range, thus ultimately, a modified, enlarged version of the original damage trail is produced which can be seen easily under an optical microscope. 42 / / 0 I •//•/• • @ • • 0 •••/•• Figure-2, The ion explosion spike mechanism for track formation in inorganic solids 43 Figure- 3. Chain cleavage and track formation in organic polymers. 44 The radiation damage trails are more susceptible to chemical reaction as compared to other bulk materials because of the large free energy associated with the disordered structure. The technique of enlarging the latent trails of radiation damage with suitable chemical agent is called chemical etching. The shape of the etched track in certain materials depend not only on the charge, mass and velocity of the incoming particle and on the nature, concentration and temperature of the etchant but also on the environmental conditions at the time of irradiations and pre-etching treatments. The shape of the track also depends on the ratio of chemical attack along the track VT, to the rate of chemical attack for the bulk material VB. This process of track revelation involves the concept of critical angle given as ec = Sm'(VBA^T) If the angle of incidence of the charged particles with respect to the surface of the detector is less than the critical angle, the tracks of the incident particles can not be revealed (Fleischer et al., 1975). As the etchant moves in the material along the damage trails at a faster rate, i.e. VT>VB , it produces a conical etch pit as shown in Figure- 4. The etching efficiency of the detection depends upon the critical angle and is given by ^ = l- Sin Oc The etch rate depends up on the composition of the material, the nature of the the damage produced by the charged particle, etchant parameters and etching time. 45 0RI6NAL SURFACE (A) 777777777777r///////7///////////////7777777777/7777P777777777 UNETCHEO TRACK H 'UNETCHED TRACK 0RI6NAL SURFACE (B) V/////r////K \ P777777777777777777777777777K117/777777 ETCHED ^ ETCHED TRACK ETCHED SURFACE TRACK UNETCHED TRACK Vat ORIGNAL SURFACE T^ (0 y/////k///////. V77777m7777777777777777K \ ?>/////> ETCHED V, SURFACE ^ T 1^ 9 = Siir^O'B VT) Figure- 4. Track-etching geometry. Preferential etching along tracks at a rate VT plus general etching at a bulk rate VB produce conical holes with a cone angle that can be shown to be Sin"'( VBA^T). The angle is larger and the pit is shallower for the less intense track on the right. (A) -shows the unetched sample (B) and (C) - shows the progressive effects of etching 46 2.4 Radon Measurement Techniques There are many techniques for measuring the concentration of radon in soil, air, groundwater and dwellings. The techniques are based on the detection of emissions from radioactive decay of radon and its daughter products. Most of the methods are based on the detection of alpha particles, some on detection of beta emission while a few utilize gamma decays. The techniques of radon measurement may be divided in two categories. (i) Instantaneous radon measurement techniques (ii) Time integrated long term radon measurement techniques 2.5 Instantaneous radon measurement techniques 2.5.1 Grab Sampling Technique This technique gives an instantaneous value of the radon concentration in air sample taken in a container for the analysis (Lucas, 1957; George, 1976). Inside the dwelling, the radon daughter products are measured by collecting airborne particulate on the filter paper for a period of 2 to 10 minutes (Raabe and Wrenn, 1969; Rolle, 1972). The filter paper sample is obtained by sucking air through a 2.5 cm diameter millipore filter type of 0.8 |im pore size at the suction rate of 20 1pm for a time period ranging from half an hour to one hour. Due to short half-lives of the radon decay products, the analyses are performed strictly within one hour after the sampling. The filter paper sample is counted using a ZnS (Ag) detector system, which is coupled to a nuclear counting system to record the counts due to disintegration of radon daughter collected on the filter paper. Grab sampling technique is suitable for large-scale surveys, because of its simplicity, minimal labor requirement and low cost. The disadvantage of this technique is that it does not give accurate information on time-averaged air concentration in dwellings. 2.5.2 Ionization Chamber Technique This is a gas filled electrode system, which is designed to detect the presence of an ionizing particle (Wrenn et al., 1975). The ionizing particle creates a pair of positive and negative ions when the gas passes through the chamber. These ions are attracted in 47 the opposite direction under the influence of electric field. The ionization chamber is operated in the range of potential varying from 100 to 300 volts so that the multiplication and recombination of the opposite pair is negligible. Ionization chamber technique can be used for measuring radon concentration down tolO Bq m''' (Pacer and Czamecki, 1980). 2.5.3 Radon Emanometry This technique is used to measure the alpha emanation rate from radon in the gas fraction of a soil or water sample by pumping the gas into a scintillation chamber using a closed circuit technique. Emanometer was the earliest device to measure radon and is still widely used for quick radon survey (Cheng and Poritt, 1981; Ramola et al., 1989; Virk, 1990). 2.6 Time integrated long term radon measurement techniques Time-integrated schemes involve the accumulation of radon over longer time periods from a few days to a week or more. In these techniques, the radon is measured either directly by detecting the alpha emission or indirectly by detecting the radioactive decay products of radon. Brief description of these techniques is given below: 2.6.1 Charcoal Technique In this technique radon can be indirectly measured by the determination of radon decay products present in the sample (Cohen and Cohen, 1983). A charcoal sampler with dimensions of the order of 10 cm can be used to collect 222Rn over a period of a day to a week. The instrument consists of a small container filled with activated charcoal. Gamma rays emitted from ^'"^Pb and ^'''Bi which are daughter products of radium, are measured. With a lower detection limit of 0.2 pCi/L for sixty hours of exposure, this instrument is suitable for measuring indoor radon levels. This technique is helpful for a period of more than a week, because after this time period most of the ^^^Rn collected at the beginning will decay out due to its 3.82 days half life period. 48 2.6.2 Plastic Bag Technique Plastic bag technique is also the time-integrated technique for radon (Sill, 1969) measurement. The sampled air collected for a period of two to three days is pumped into a bag which is impermeable to radon gas. For alpha counting, the integrated sample during analysis is transferred to the Scintillation flask. Concentration as low as 0.01 pCi/L can be measured using this technique. 2.6.3 Thermo luminescence Detector Technique This is a process in which light is emitted by a substance when it is heated and which can be attributed to the previous exposure to ionizing radiation. When a crystal is exposed to ionizing radiation, electron hole ionization pairs are created and some of them combine with the trapped charges. Thermoluminescence detectors, used for radon measurement are very thin wafers (760 m of calcium sulphate doped with dysprosium in a matrix of Teflon), which are mainly sensitive to alpha radiation (McCurdy et al., 1969; Pacer and Czamecki, 1980). These .detectors are typically exposed for 30 days in the uranium exploration program and then processed for their thermoluminescence peaks. 2.6.4 Alpha Meter Technique This technique employs a solid-state alpha particle detector counter assembly. The alpha particle detector is a silicon-diffused junction with an active area of 400 mm^. When an alpha particle enters the n-p junction, a number of electron hole pairs are generated which are proportional to the energy of alpha particle. The flow of current is sensed and amplified many hundreds of times to produce a pulse that may then be counted. The alpha counts are displayed on the light emitting diode (LED) display (Warren, 1977). The other instrumental method of measuring the radon flux includes the alpha cards with a central collector for recording radon daughters (Dyck et al., 1983). The detector records the alpha particles emanated by radon isotopes and their alpha emitting daughters. This instrument does not register any alpha particle having energy less than 1 MeV. 49 2.6.5 Track Etch Technique Track etch technique is one of the most widely used techniques for radon measurement (Klies et al., 1992; Bhagwat, 1993; Ramchandran, 1998; Kumar et al., 2003; Mahur et al., 2006). In this technique, the monitoring device is a solid state nuclear track detector (SSNTD). The principle of detection consists of the damage imparted in the detector material by alpha particles from radon and its decay products. The damage imparted in the detector is observed under optical microscope. Heavily ionizing particles passing through insulating media leave narrow trails of damage on an atomic scale (-30- 100 A). With each alpha particle producing a distinguishable track, these latent tracks can be enlarged to microscopically visible size by the method of chemical etching in which the damaged region reacts at faster rate with a chemical reagent. Number of tracks per unit area in the detector is proportional to the average exposure rate and exposure time. Exposure time can range up to a year or more, if desired, using improved plastic track detectors which retain alpha tracks without fading for a very long time at ambient temperatures. Though several detector materials have been developed but LR-115 and CR-39 are the two most popular track detectors used for radon dosimetry. The advantage of track etch technique is its simpUcity, no involvement of electronics, low cost and feasibility in extensive radon surveys. A strong drawback in the use of solid-state nuclear track detectors is that they only integrate the received flux of particles and don't provide time dependent response. Other demerit of track etch technique is its poor sensitivity for integrated time periods less than one month, hi studies of indoor radon, monitoring time period of about three months is adequate. Track etch technique was used in the present study. In this technique LR-115 type II track etch detector was employed for measuring the Potential Alpha Energy Concentration (PAEC) of radon progeny in Working Level (WL) units. LR-115 type- II films are sensitive to a particles of energy range 0.1 to 4 MeV and are unaffected by electrons. X-rays and 7-rays (Jonsson, 1981). Due to its being sensitive to only a specific range of energy, it is ideal for the use as radon dosimeter even in bare mode as it is free from plate out effect (Abu-Jarad et al., 1980). The pieces of the detector film of size 2x2 cm, fixed on a thick flat card are exposed in "Bare mode" by hanging the cards on the wall in the room for a period of few months such that the detector views a hemisphere of radius at least 6.9 cm, the range of 50 ^'''Po a-particles in the air. No surface should be closer than this range as the decay products would act as an indeterminate a-particles sources. Detectors are mounted vertical and the locations are so selected that the dust collection on the detectors be minimum. After exposure, the latent tracks due to radiation damage produced by alpha particles from radon and its progeny are revealed by chemical etching in a constant temperature water bath (Figure -4). The counting of alpha tracks are done using a binocular optical research microscope as shown in Figure- 5. 51 Figure-4 Constant temperature water bath 52 Figure-S Optical binocular optical research microscope with a magnification of 400 x 53 2.7 Radon and Thoron measurements using twin chamber dosimeters Twin cup radon dosimeter was used in present study for the measurement of indoor and outdoor radon concentrations. The alpha sensitive plastic track detector, pelliculable LR-115 Type II (Manufactured by Kodak Pathe, France) is used. It is a 12 \xm thick film red dyed cellulose nitrate emulsion coated on inert polyester base of 100 ^m thickness and has maximum sensitivity for alpha particles, fission fiiagmentsan d ionizing particles with high enough LET. It is widely used for particle detection of ionizing particles, high-resolution neutron radiogrq)hic uses, alpha radiography, cosmic ray investigations etc. The film can be used to record the tracks of protons with an energy <100 KeV and alpha particles with energy -0.06 to 6 MeV. It is insensitive to X or y- rays, photons, electrons and high-energy protons. The sensitivity is claimed to be one of the best amongst any other plastic detectors. For fast neutrons, it has low detection efficiency (10"^ track/neutron) (Khan, 1975). Track etching mechanism of pelliculable LR-115 has been studied at different temperatures ranging firam 30 °C to 60 "C for different etching times and the calculated value of activation energy is 0.1845 eV (Paul and Bose, 1980). The recommended etching conditions given by the manufacturer are 2.5N NaOH, 60°C, 65 to 95 minutes without agitation. Another suitable etching condition reported is 2.5N NaOH, 60*'C, 60 to 70 minutes with stirring (Costa-Riberio and Labao, 1975). The dosimeter has been developed at Bhabha Atomic Research Centre (BARC) and is shown in Figure- 6. Each cylindrical chamber has a length of 4.1 cm and a radius of 3.1 cm. One piece of the detector film (SSNTD) placed in compartment M measures radon only which diffuses into it fi-om the ambient air through a semi-permeable membrane. It allows the build up of about 90% of radon gas in the compartment and suppresses thoron gas concentration by more than 99%. The mean time for radon to reach the steady- state concentration inside the cup is about 4.5 hour. Glass fiber filterpape r in the compartment F allows both radon and thoron gases to diffuse in and hence the tracks on second piece of the detector film placed in this chamber are related to the concentrations of both the gases. 54 Third piece of the detector film exposed in bare mode (placed on the outer surface of the dosimeter) registers alpha tracks attributed to both the gases and their alpha- emitting progeny, namely ^' Po ^''^Po, '^'^Po, and ^'^Po. All the detectors are exposed for 90-100 days. After exposure the films are etched. The detectors are pre-sparked using spark counter as shown in Figure-7 (Cross and Tommasino, 1970) to fully develop the partially etched track holes. The tracks are then counted at the voltage corresponding to the plateau region of the counter. The concentrations are derived from the observed track densities using appropriate calibration factors. The calibration factors depend upon various parameters such as membrane and filter characteristics as well as on the energy of the alpha particles for the cup mode exposure, the parameters of the etching process and spark counting characteristics. 55 Bare im (Ouaghter products) Figure -6 Twin cup radon- thoron dosimeter 56 Fig-7 Spark counter set up 57 2.8 Measurement of radon exhalation rate Radon exhalation rate is of prime importance for the estimation of radiation risk from various materials. "Sealed Can Technique" (Fleischer and Morgo- campero., 1978; Mahur et al., 2008) is widely used for radon exhalation measurements in solid samples. SSNTD is fixed on the top inside the cylindrical "Can" as shown in Figure-8. Sample of known amount is placed at the base of the Can. The Cans are sealed for 90-100 days. Thus the lower sensitive part of the detector is exposed freelyt o the emergent radon from the sample in the Can so that it could record the tracks of alpha particles resulting from the decay of radon in the remaining volume of the Can and from ^'^Po deposited on the inner walls of the Can. Radon and its daughters reach equilibrium in about four hours and hence the equilibrium activity of emergent radon can be obtained from the geometry of the Can and the time of exposure. For the study of the radon exhalation rates from building and construction materials like bricks and flooring materials like mosaic, marble, granite, ceramic tile etc., plastic Can of known dimension is sealed by plasticin to the individual building material. In each Can a SSNTD is fixed at the top inside the Can ( Figure-9) After the exposure the detectors are etched in suitable etchants in constant temperature water bath for revelation of tracks. The resulting a- particle tracks are counted using an optical microscope. The activity is obtained from the track density in the etched detectors using the calibration factor obtained from calibration experiment. Following expression gives the exhalation rate (Khan et al., 1992, Fleischer and Morgo- campero, 1978 and Mahur et al., 2008): CVA Ex= T +1 i^--l } (1) where Ex is the Radon exhalation rate (Bq m'^ h''); C, the litegrated radon exposure as measured by LR-115 type II plastic track detector (Bq m'^ h ); V, the effective volume of the Can (m^); X, the decay constant for radon (h''); T, the exposure time (h) and A is the area covered by the Can (m^). 58 LR-I15 IECM-^ JO Figure.8. Experimental set up for the measurement of radon exhalation rate using "Sealed Can Technique" 59 LR-115 Type n Nuclear Track Detector -Plastic Can BuJMiiig Dfoterial Figure 9: Assembly for the measurement of radon exhalation rate using "Can technique" 60 2.9 Natural radioactivity measurements There are many techniques for the measurement of natural radioactivity in the samples. We present three techniques used in the present study for estimation of the natural radionuclides, uranium (^^*U), thorium (^^^Th) and potassium ('^^K) in coal -fly ash, rocks, soil, sand and building construction material samples. 2.9.1 Gamma-ray spectroscopy technique using Nal (Tl) detector A low level gamma ray spectrometric set up at National Geophysical Research Institute, Hyderabad, was used for estimation of the natural radionuclides, uranium (^^*U), thorium (^^^Th) and potassium C*°K) in coal and fly ash samples. About 250 g of each sample was packed in plastic containers and sealed for four weeks (El-Arabi, 2005) for ^*U and ^^Th to attain secular equilibrium with their decay products and to prevent ^^^Rn and ^^°Rn loss. The detector consisted of a 5" x6" Nal (Tl) crystal coupled to a 5" diameter photomultiplier tube. A 256- charmel data set covering 0- 3 MeV is obtained through a Multi Channel Analyzer (MCA) card (on a computer) that provided a gain- Stabilized spectrum. U and Th were assessed from the intensity of the gamma ray peaks of their daughters, whereas '^^K was measured directly from its own gamma ray of 1.46 MeV. 2.9.2 Gamma-ray spectroscopy technique using HPGe detector Gamma ray spectrometric measurements were carried out at Inter-University Accelerator Centre, New Delhi using a coaxial n-type HPGe detector (EG&G, ORTEC, Oak Ridge, USA) for estimation of the natural radionuclides, uranium (^'^^U), thorium (^^^Th) and potassium ("^^K) in rock and soil samples. Photograph of gamma ray spectrometric set is shown m Figure-10. Before measurements, the containers having the samples were kept sealed for about 4 weeks in order to reach equilibrium of the ^^*U and ^^^Th and their respective progenies. The samples were then subjected to high resolution gamma spectroscopic analysis. HPGe detector (EG«feG, ORTEC, Oak Ridge, USA) having a resolution of 2.0 keV at 1332 keV and a relative efficiency of 20% was placed in 4" shield of lead bricks 61 on all sides to reduce the background radiation from building materials and cosmic rays ( Kumar et, al; 2001). The detector was coupled to a PC based 4K multi channel analyzer and an ADC for data acquisition. For activity measurements the samples were counted for a period of 72000 seconds. The activity concentration of "^^K (CK) was measured directly by its own gamma ray of 1461 keV. As ^^*U and ^^^Th are not directly gamma emitters, their activity concentrations (Cu and C-n,) were measured through gamma rays of their decay products. The spectra, were analyzed using the locally developed software "CANDLE (Collection and Analysis of Nuclear Data using Linux Net work)" an example shown in Figure-11. 2.10 Fission track registration technique For the uranium analyses in some soil, fly ash and building material samples fission track registration technique was used. The method is highly reliable, sensitive and simple. At the same time it has the potential capability of micro mapping even for sub ppb levels of fissionable impurity. The fission fragments resulting from (n, f) reaction on ^^U are observed by track etch detectors kept in contact with the sample or standard material . From the number of tracks in the detector, the uranium concentrations in the samples can be determined (Singh et al., 1998). Thermal neutrons for producing fission are obtained fi^om a nuclear reactor. All samples were grinded properly and sieved through 100 mesh. A homogenous mixture of accurately weighed sample powder and methyl cellulose in the ratio 1:2 ratio by weight was made. 200 mg of this mixture a thin pellet of about 1 mm thick and 1.3 cm in diameter was prepared by a hydraulic pellet machine applying a pressure of about 5 t/ cm . Pellets of standard glass of known uranium concentration (Azam and Prasad, 1989) were also prepared in the similar manner. Each of these pellets was sand wiched between a pair of Makrofol -KG plastic track detector pieces of same size. All the pellets of sample and standard glass were enclosed in an aluminum capsule and sealed tightly to make the intimate contact. This assembly was irradiated with a thermal neutron fluence of about lO'^ cm'^ (nvt) at APSARA reactor, Bhabha Atomic Resaerch Centre Mumbai, India. After irradiation the detector pieces were separated fi-om the pellets, and etched in 6.25 N KOH solution at 60" for 20 minutes in a constant temperature water bath to reveal the fission tracks. 62 Fig. 10 Gamma ray spectrometric set at Inter-University Accelerator Centre, New Delhi 63 XwafleJ^xirm * K-te if- I •# s S«i3 7MJ snu HSBT OWl OK? Fig«re-I I An example of gamma ray spectnim 64 References Abu-Jarad, F., Fremlin, J H., Bull, R., 1980. A study of radon emitted from building materials using plastic- track detectors. Phys. Med.Biol.25,4 683-694. Azam, A., Prasad, R., 1989. Trace element analysis of uranium of soil and plant samples using fission track registration technique. J. Radioanal. Nucl. Chem., 1999-202. Bonfiglioli, G., Ferro A., Mojeri A. J., 1961. Electron microscope investigation on the nature of tracks of fission products in mica. Appl. Phys., 32,2499-2503. Benton, E.V. 1967. USNRDL-TR-67-80, U.S. Naval Rad. Def Lab. San Francisco, California, U.S.A. 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Sci., NS-22, 645. Warren, R. K., 1977. Geophysics 42, 982. 67 CHAPTER -3 MEASUREl/INT OF INDOOR wr > * !N INDIAN \jai m ENVlOmiBNT Chapter-Ill 3.1 Introduction The risk of lung cancer for workers in uranium mines is known for a long time and is related to radon exposure (Sevc et, al., 1976). Radon is generated from radium present in soil, building materials and even water. Radon is a noble gas in the uranium decay series with a fairly long half life of 3.82 days. Being an inert gas it can easily disperse into the atmosphere as soon as it is released. The solid alpha active decay products of radon ( ' Po, ^''*Po) become airborne and attach themselves to the dust particles, aerosols and water droplets in the atmosphere. When inhaled, these solid decay products along with air may get deposited in the trachea-bronchial (T-B) and pulmonary (?) region of lungs resulting in the continuous irradiation by a-particles on the cells which may cause lung cancer (Lubin, 1994; Samet et al., 1989). Radon in dwellings is generated from radium present or existing or accumulated in soil, construction materials and water. Radon and its daughter products may pose a significant health hazard, especially when concentrated in some enclosures such as underground mines, caves, cellars or poorly ventilated and badly designed houses. Thus radon concentration in dwellings is important due to the health risk and to determine the design of control strategies. Indoor radon concentration depends in a complex way on the characteristic of the soil, the type of building structure, ventilation condition and occupant's behavior. In homes the predominant source of radon in indoor air is the soil beneath structures, but building materials and water used in the homes and in a few cases natural gas may also contribute (Nero and Nazaroof, 1984). The concentrations of radium in soil and in rocks vary several orders of magnitude. This variation in source strength results in the variation in radon concentrations among dwellings. Keeping the radiation hazards of radon for general population in mind, it is quite important to make a systematic study of the indoor radon concentration in Indian dwellings. For this purpose, radon measurements have been carried out in a number of dwellings in the cities of different states of India Exposure to Radon ( Rn) and its progeny in indoor atmosphere can result in significant inhalation risk to population particularly to those living in homes with much 68 higher levels of radon. All radiations gives a world average value of 2.4 mSv for the annual effective dose equivalent from natural back ground radiation of which 1.4 mSv comes from the radon , thoron and their daughter products (Nambi et al., 1986; UNSCEAR, 1993). ^^Rn is an inert radioactive gas with a half-life of 3.82 days and belongs to the radioactive uranium series. Thoron, ^^°Rn, is a natural decay product of thorium series. It has a half-life of 55.6 seconds and also emits alpha rays. Some of the daughter products from radioactive decay of radon (such as polonium) are toxic. Solid decay products of radon form a very fine dust that is both toxic and radioactive and can potentially stick in the lungs after inhalation and do far more damage than the radon itself (Darby et al., 2001). Although U and Th occur in virtually all types of rocks, sands and soils, their concentrations vary with specific sites and geological materials. As an inert gas, radon can move fi^eelythroug h the soil fi-om its source; the distances are determined by factors such as rate of diffusion, effective permeability of the soil and by its own half- life. Radon progenies might be inhaled and deposited more or less deeply onto the bronchio-pulmonary tree, depending upon the granulometry of the particles on which they become attached. Measurements of indoor radon are of importance because the radiation dose to human population due to inhalation of radon and its daughters contributes more than 50% of the total dose from natural sources (UNSCEAR, 1993) and large scale studies have been carried out world wide. On the other hand there exists only a few studies relating to passive measurements of thoron (Doi and Kobayashi, 1994; Doi et al., 1994). It is assumed that the inhalation dose to the human beings from thoron and its progeny is negligible although recent studies in many countries have revealed that this may not be entirely correct (Steinhauser et al., 1994) It is well known that exposure of population to high concentrations of radon and its daughters for a long period leads to pathological effects like the respiratory functional changes and the occurrence of lung cancer (BEIR VI, 1999). The exposure of human beings to ionizing radiation from natural sources is a continuing and inescapable feature of life on earth. There are two main contributors to natural radiation exposures: high- energy cosmic ray particles incident on the earth's atmosphere and radioactive nuclides that originated in the earth's crust and are present everywhere in the environment, including the human body itself 69 3.2 Radon in workplaces Radon can present a hazard in a wide range of workplaces other than mines. While this includes below ground workplaces such as subways, tunnels, stores, show caves, closed-out mines open to visitors, and radon spas, the majority of such workplaces will be above groimd. Some proportion of normal above ground workplaces such as factories, shops, schools and offices will be affected. In buildings with high radon levels, the main mechanism for the entry of radon is the pressure driven flow of gas from soil through cracks in the floor. This flow arises because buildings are normally at a slight under pressure with respect to their surroundings. This under pressure is a consequence of the air inside buildings being warmer than that outside, especially in temperate and cold regions, and also of the drawing effect of the wind blowing over chimneys and other openings. However, various other mechanisms can affect the concentrations of radon in dwellings. Most building materials produce some radon but building materials of certain types can act as significant sources of indoor radon. Such building materials have a combination of elevated levels of Ra and a high porosity that allows the radon gas to escape. 3.3 Action levels limits The radon concentration at which measures would need to be undertaken to reduce radon exposures is known as the action level. The action level for radon in the workplace is given in IAEA report, 2003 as a yearly average concentration of 1000 Bq m^ which would, for an assumed occupancy of 2000 hours per year, equate to an effective dose of about 6 mSv. This value of 1000 Bq m'^ is at the midpoint of the range 500-1500 Bqm' recommended by the International Commission on Radiological Protection (ICRP), and some regulatory bodies may wish to adopt a lower level than was specified in IAEA report, 2003. It should be noted that the range of values given by the ICRP was based on an assumed equilibrium factor between radon and its progeny of 0.4. There is a practical advantage to adopting a single value for the action level which may be applied in all situations irrespective of the equilibrium factor. Nevertheless, although 70 not explicitly stated in IAEA report, 2003, other action levels may be appropriate if the equilibrium factor is significantly different from 0.4. For example, if the actual equilibrium factor is 0.8, then in theory at least a value for the action level of 500 Bq m'^ might be appropriate. Nevertheless, this action level for radon in workplaces does not mark a boundary between 'safe' and 'unsafe' exposures. Unless the exposure is excluded or the practice or the source is exempted, regulatory bodies are free to establish an occupational action level below 1000 Bq m'^ if national circumstances make this practicable. 3.4 Measurement of radon and its progeny in Indian dwellings Among many surveys carried out for radon studies, the largest and most recent of these was an international study led by the National Cancer Institute (NCI), USA which examined the data on 68,000 underground miners who were exposed to a wide range of radon levels. The study of miners shows the probability of death due to lung cancer five times more than expected for the general population. Several surveys performed in Europe and North America. (Samet et al., 1989; McGregor et al, 1980; Swedjemark et al, 1984; Nero et al., 1986; Cohen et al., 1995) revealed that some countries have high radon concentration in many of their dwellings. 3.5 Materials and methods LR-115 type 11 Solid Sate Nuclear Detectors (SSNTDs) were employed for measuring the Potential Alpha Energy Concentration (PAEC) of radon progeny in Working Level (WL) units. The pieces of the detector film of size (2cm x 2 cm), fixedo n a thick flat card were exposed in "Bare" mode by hanging the cards on the wall in the room for a period of 90-100 days such that the detector viewed a hemisphere of radius at least 6.9 cm, the range of ^''^Po a-particles in the air. No surface was closer than this range as the decay products would act as an indeterminate a-particles sources. Detectors were mounted vertical and the locations were so selected that the dust collection on the detectors be minimum. After exposure, the detectors were collected and brought back to the laboratory for analyses. 71 The films were etched in 2.5 NaOH solution at 60°C for 90 minutes in a constant temperature water bath. The counting of alpha tracks was done using a binocular optical research microscope with a magnification of 400X. At least 300-400 tracks were counted for each detector film to keep the statistical error of counting to a minimum. The track density registered in the bare detector will, therefore, be a function of radon progeny concentration in air. The radon concentration in Bqm''' was estimated fi-om working level by using the following equation (Kumar et al, 2003; Kumar and Prasad, 2005; Mahur, et al, 2006): RnC(Bqin-^) = 3700 x WL Rn Where F is known as the equilibrium factor and varies fi"om 0.38 to 0.7 with the average value of 0.45 as found in Indian dwellings. Thus we have taken 0.45 as the value of F for finding the radon concentration (RnC). Value of 0.4 is suggested by UNSEAR, 2000. To obtain the Potential Alpha Energy Concentration (PAEC) of radon progeny in mWL it is essential that LR-115 type II detector films should be calibrated with a known radon concentration under the conditions almost similar to those which prevail in Indian dwellings. For this purpose, the detectors were calibrated in a radon exposure chamber at the facility available in Environmental Assessment Division of Bhabha Atomic Research Centre, Mumbai. The mean calibration factor for LR-115 type II detector was found to be 442 tracks cm'^d''per WL (Jojo etal., 1994; Singh etal., 1997). 3.6. Results and discussion 3.6.1 Radon levels in dwellings of Palampur and Baijnath (Himachal Pradesh) The measurements of indoor radon (^^^Rn) concentration in about 45 dwellings of the cities of Baijnath and Palampur (Himachal Pradesh) were carried out to assess the variability of expected exposure of the population to radon and its progeny. Indoor Rn exposure depends in a complex way on the characteristics of the soil, the type and details of the building structure, meteorology, ventilation conditions and occupant's behaviour. 72 State of Himachal Pradesh of India is well loiown for uranium mineralization (Narayanan et al., 1979) and was selected as a study site since it has been reported that the region has natural uranium and thorium concentration higher than the world average value of 30 Bq kg'' (UNSCEAR, 1993). Some earlier studies have reported very high values of soil-gas radon in Himachal Pradesh (Ramola, et al., 1987; Virk and Sharma, 1998). Thus the programme was undertaken to carry out radon measurements in some dwellings in the cities of Palampur and Baijnath in Himachal Pradesh. Radon dosimeters containing LR-115 films were placed in 30 rooms in different dwellings of the Palampur and 15 dwellings in Baijnath city, The detector films (LR-115 type II) were exposed in the living rooms, bed rooms, office rooms, kitchen etc, for 90 days. Tables 1 & 2 present the measured PAEC values of radon daughters in mWL units, radon concentration in Bqm'^ and annual effective dose equivalents in mSv. 73 Table-1 Indoor radon levels in dwellings of Palampur city, Himachal Pradesh, India Annual Potential alpha Radon activity S.No. Type of room effective dose activity (mWL) (Bqm"^) (mSv) 1. Bed room 11.0 91.1 3.4 2. Bed room 13.1 107.8 4.1 3. Living room • 8.8 72.5 2.7 4. Living room 7.9 65.0 2.4 5. Open Space 5.2 42.5 1.6 6. Bed room 7.2 59.5 2.2 7. Bed room 7.4 61.3 2.3 8. Kitciien 7.6 63.2 2.4 9. Living room 7.4 61.3 2.3 10. Living room 10.4 85.5 3.2 11. Bed room 14.4 118.5 4.5 12. Bed room 13.4 110.3 4.2 13. Living room 12.2 100.5 3.8 14. Kitchen 20.4 168.4 6.4 15. Kitchen 17.7 145.5 5.5 16. Living room 12.2 100.5 3.8 17. Living room 8.1 66.9 2.5 18. Bed room • 14.4 118.5 4.5 19. Kitchen 9.6 79.3 3.0 20. Kitchen 9.3 76.8 2.9 21. Living room 11.6 93.0 3.5 22. Bed room 13.8 113.4 4.3 23. Bed room 12.8 106.0 4.0 24. Bed room 11.5 94.8 3.6 25. Kitchen 15.1 124.6 4.7 26. Kitchen 16.4 134.9 5.1 27. Bed room 10.0 82.5 3.1 28. Living room 10.2 84.2 3.2 29. Living room 13.4 110.3 4.2 30. Bed room 16.2 133.2 5.0 • Average value 11.6 95.7 3.6 S.D. 3.4 28.6 1.0 RelStd. % . 29.3 29.8 27.7 74 Table-2. Indoor radon levels in dwellings of Baijnath (H.P.) Potential alpha Annual Radon activity S.No. Type of room activity effective dose (Bqm'^) (mWL) (mSv) 1. Kitchen 30.0 247.0 9.4 2. Kitchen 32.3 265.5 10.0 3. Kitchen 26.5 218.0 8.3 4. Kitchen 30.3 249.3 9.5 5. Bed room 11.4 93.7 3.6 6. Bed room 21.6 177.8 6.8 7. Bed room 22.6 186.0 7.0 8. Bed room 22.0 180.0 6.9 9. Bed room 13.4 110.1 4.1 10. Bed room 16.0 131.7 5.0 11. Living room 7.5 61.7 2.3 12. Living room 8.1 66.6 2.5 13. Living room 5.1 41.9 1.6 14. Living room 10.2 84.2 3.2 15. Living room 10.6 87.8 3.3 Average value 17.8 146.8 5.6 S.D. 8.9 72.9 2.8 Rel.Std.% 49.7 49.7 49.8 75 The radiation doses to the basal layer of epithelium are estimated in terms of the effective dose equivalents using the conversion factor of 9 mSv/WLM suggested by ICRP-65 (1993). The measured potential alpha activity in different rooms in Palampur city varies from 5.2 to 20.4 mWL with an average of 11,6 mWL. Annual effective dose received by the inhalation of radon progeny are found to vary from 1.6 to 6.4 mSv and radon concentration varies from 42.5 to 168.4 Bqm with an average value of 95.7 Bqm . In dwellings of Baijnath city potential alpha activity in different rooms varies from 5.1 to 32.3 mWL with an average of 17.8 mWL. Radon concentration varies from 41.9 to 265.5 Bqm"^ with an average value 146.8 Bqm'^ and annual effective dose from 1.6 to 10.0 mSv with an average value 5.6 mSv. From the results it can be observed that radon concentration is higher in the dwellings of two cities of Himachal Pradesh as compared to our measurements in other neighboring states (Khan et al., 1995; Singh et al., 1999). Jatinder Kimiar et al., (1994) have made measurements for radon concentration in dwellings of some villages of Himachal Pradesh and found the average values between 660 and 1060 Bqm'^. Thus the present values are lower. This may be due to the lower uranium concentration in the soil of the region and the ventilation in the dwellings etc. The system of dose limitation recommended by the International Commission on Radiological Protection (ICRP) applies for protection against radon and progenies also. ICRP-65 (1993) .summarizes the health effects of inhaled radon and its progenies and give recommendations/guidelines for the control of exposure to high levels of radon encountered in dwellings and in work places. The commission in its report has recommended that some remedial measures against radon in dwellings are always justified above a continued effective annual dose of 10 mSv. Further, it also recommends that the action levels should be set within a range of 3-10 mSv by appropriate regulatory authorities. On the basis of these recommendations, it is observed that the radon levels in dwellings surveyed in Palampur and Baijnath are in the action level limit. 76 3.6.2 Radon levels in the dwellings along the south west coast of Kerala High Background Radiation Areas (HBRA) Large scale residential radon surveys have been carried out in several countries including some survey in elevated natural background radiations present in some parts of the world, called as High Background Radiation Areas (HBRA).The object of this study is to estimate the radiation risk due to low dose. Among many surveys carried out for radon studies, the largest and most recent of these was an international study led by the National Cancer Institute (NCI), USA which examined the data on 68,000 underground miners who were exposed to a wide range of radon levels (BEIR VI Report, 1999). The dwellings selected for the present radon study are situated along the south west coast of Kerala in three towns: Eravipuram, Panmana and Thankassery in KoUam district. Thankassery and Panmana is in the vicinity of the High Back Ground Area (HBRA), whereas Eravipuram is about five to six Km away from HBRA. Radon and its progeny were measured using Solid State Nuclear Track Detectors.Tables 3-5 presents the measured PAEC values of radon daughters in mWL units, radon concentration in Bqm' and annual effective dose equivalents in mSv in Eravipuram. Panmana and Thankassery respectively. »a Atad /• * 77 Table-3 Indoor radon levels in dwellings of Eravipuram (Kerala ) Track Potential Radon Annual density alpha Code No. Location activitv effective dose (Tr/sq activity (Bqm-^) (mSv) cm/day) (raWL) Jll Living room 9.6 21.7 200.7 6.8 J21 Living room 10.9 24.6 227.5 7.7 J31 Living room 8.5 19.2 177.6 6.0 J41 Living room 5.6 12.6 116.5 3.9 J61 Living room L3 2.9 26.8 0.9 J71 Living room 4.1 9.2 85.1 2.9 J81 Living room 9.6 21.7 200.7 6.8 J12 Bed room 4.1 9.2 85.1 2.9 J22 Bed room 10.9 24.6 227.5 7.7 J32 Bed room 9.2 20.8 192.4 6.5 J42 Bed room 6.0 13.6 125.8 4.3 J62 Bed room 6.5 14.7 135.9 4.6 J72 Bed room 5.3 11.9 110.1 3.8 J82 Bed room 3.0 6.7 61.9 2.1 J13 Kitclien 5.9 13.3 123.0 4.2 J23 Kitchen 7.0 15.7 145.2 4.9 J33 Kitchen 5.3 11.9 110.1 3.7 J43 Kitchen 6.7 15.0 138.7 4.7 J63 Kitchen 3.1 6.9 63.8 2.2 J73 Kitchen 2.5 5.6 51.8 1.8 J83 Kitchen 7.7 17.3 160.0 5.4 Average 6.3 14.2 131.7 4.5 S.D. 2.7 6.1 56.6 1.9 Rel.Std.% 42.8 42.9 42.9 42.2 78 Table-4 Indoor radon levels in dwellings of Panmana (Kerala) Track Potential Radon Annual density alpha Code No. Location activity effective dose ( Tr/sq activity (Bqm-^) (mSv) cm/day) (mWL) Rll Living room 2.1 4.6 42.5 1.5 R21 Living room 18.4 41.5 383.8 13.0 R31 Living room 16.6 37.5 346.8 11.8 R41 Living room 9.5 21.4 198.1 6.7 R61 Living room 6.9 15.6 144.3 4.9 R81 Living room 7.9 17.7 163.7 5.6 R12 Bed room 5.1 11.4 105.5 3.6 R22 Bed room 16.7 37.6 347.8 11.8 R32 Bed room 14.5 32.6 301.5 10.2 R42 Bed room 11.7 26.3 243.3 8.3 R52 Bed room 14.6 33.0 305.3 10.3 R62 Bed room 6.9 15.4 142.5 4.9 R82 Bed room 8.5 19.1 176.7 6.0 R13 Kitchen 2.4 5.4 49.9 1.7 R23 Kitchen 18.8 42.5 393.1 13.3 R33 Kitchen 9.1 20.4 188.7 6.4 R43 Kitchen 11.6 26.1 241.4 8.2 R63 Kitchen 8.1 18.3 169.2 5.7 R83 Kitchen 13.2 29.8 275.6 9.4 Average 10.7 24.0 222.1 7.5 S.D. 4.9 11.1 103.0 3.5 Rel. Std.% 45.8 46.2 46.4 46.7 79 Table-5 Indoor radon levels in dwellings of Thankassery town (Kerala) Track Potential Radon Annual Code No. Location density alpha activitv effective dose (Tr/Sq activity (Bqm^) (mSv) Cm/Day) (mWL) Sll Living room 12.8 28.9 237.7 9.1 S21 Living room 8.1 18.2 150.1 5.7 S31 Living room 6.9 15.5 128.0 4.9 S41 Living room 7.1 16.0 131.7 5.1 S51 Living room 7.8 17.6 145.1 5.5 S61 Living room 5.5. 12.4 102.1 3.9 S71 Living room 6.9 15.5 127.6 4.9 S81 Living room 7.2 16.3 134.7 5.1 S12 Bed room 12.7 28.7 236.1 9.0 S22 Bed room 4.9 11.0 91.2 3.5 S32 Bed room 6.9 15.6 128.9 4.9 S42 Bed room 5.7 12.8 105.8 4.0 S52 Bed room 6.6 14.8 121.8 4.6 S62 Bed room 6.0 13.5 111.8 4.3 S72 Bed room 8.1 18.3 150.5 5.7 S82 Bed room 7.9 17.8 147.0 5.6 S13 Kitchen 20.1 45.4 373.3 14.2 S23 Kitchen 2.4 5.3 44.3 1.7 S33 Kitchen 8.7 19.6 161.3 6.1 S43 Kitchen 5.4 12.3 101.2 3.9 S53 Kitchen 7.2 16.3 134.7 5.1 S63 Kitchen 7.0 15.8 130.4 5.0 S73 Kitchen 7.1 16.1 132.8 5.1 S83 Kitchen 7.7 17.4 143.6 5.5 Average Viilu e 7.8 17.5 144.7 5.5 S.D. 3.3 7.5 61.5 2.3 Rel. Std.% 42.3 42.8 42.5 41.8 80 The measured radon concentration in the dwellings of Eravipuram varies from 26.8 Bqm'^ to 227.5 Bqm'^ with an average value of 131.7 Bqm'^ and in dwellings of Panmana it varies from 42.5 Bqm to 393.1 Bqm with an average value of 222.1 Bqm . The radon activity may vary with the ventilation conditions, type of construction and other factors. Majority of the houses built in the region are constructed with brick walls and the remaining houses have either wooden or thatched walls. 34% of the houses are made up of concrete roofs, about 38% are tiled, 12% are thatched and remaining houses have either asbestos or galvanized iron sheets roofs. About 84% of the houses have cement flooring, 8% have tiled flooring and remaining have bare soil flooring. The dwellings in Panmana town situated in the vicinity of HBRA show more radon activity than the dwellings of Eravipuram, the town far from HBRA. Living rooms show more activities than from the bed rooms and kitchens. The variation may be due to ventilation conditions. Amiual effective dose equivalent in Eravipuram varies from 0.9 mSv to 7.7 mSv with an average value of 4.5 mSv whereas in Panmana it varies from 1.5 mSv to 13.3 mSv with an average value 7.5 mSv. The measured radon concentration in the dwellings of Thankassery town varies from 44.3 Bqm"^ to 373.3 Bqm"^ with an average value of 144.7 Bqm' . In the dwellings of Panmana town situated in the vicinity of High Background Radiation Area HBRA shows more radon activity than the dwellings of Thankassery. Living rooms show more activities than from the bed rooms and kitchens. The variation may be due to ventilation conditions. Annual effective dose equivalent in Thankassery town varies from 1.7 mSv to 14.2 mSv with an average value of 5.5 mSv . 3.6.3 Radon levels in some dwellings around Nuclear Atomic Power Plant, Narora, Bulandshahr (Uttar Pradesh) Narora is located on the banks of Ganges river in the district Bulandshahar of U.P. (India). Nuclear Atomic Power Plant (NAPP) has two reactors rated at 220 MWe. The plant is located in seismic zone and is about 150 km away from New Delhi, capital of India. The measurements of radon and its daughters concentration has been carried out in dwellings of some villages around the Nuclear Atomic Power Plant (NAPP) at Narora to study the effect of its operation. The results of the present measurements of ^^^Rn concentration in WL units and radon activity in Bqm"^ inside the dwellings of four 81 villages around the atomic power plant are presented in Tables 6 to 9. Significant variations of radon concentration were found in different type of rooms. Radon concentration in dwellings of different villages varies from 93.7 to 195.7 Bqm"^ in bed rooms; from 65.0 to 199.8 Bqm"^ in living rooms from 111.8 to 220.4 Bqm'^ in kitchens from 61.3 to 97.8 Bqm"^ in varandas and 42.8 to 71.5 Bqm'^ in court yards (open space). The radon levels in the indoor atmosphere (bed rooms, living rooms & kitchens) are much higher than in varandas or court yards (open space) of the dwellings. This may be due to better ventilation. Present values lie within the range of our earlier large scale radon measurements in Indian dwellings: from 67 to 118 Bqm'^ (Khan et al., 1989); from 65 to 156 Bqm"^ (Singh et al, 1997) from 15 to 183 Bqm"^ (Singh et al, 1999). Values of radon activity in Nandpur village varies from 51.8 to 198.2 Bqm'^ with an average value of 125.2 Bqm"^. Annual effective dose varies from 2.0 to 7.5 mSv with an average value of 4.8 mSv. Radon activity in Silhari village varies from 42.8 to 175.9 Bqm' with an average value 165.3 Bqm and annual effective dose varies from 1.6 to 8.2 mSv with an average of 6.3 mSv. Radon activity in Niwari village varies from 71.5 to 183.4 Bqm"^ with an average value of 130.3 Bqm and annual effective dose varies from 0.8 to 7.0 mSv with an average value of 4.8 mSv. Radon activity in Ramghat village varies from 59.5 to 206.4 Bqm'^ with an average value 150.3 Bqm'^ and annual effective dose varies from 2.2 to 7.9 mSv with an average of 4.8 mSv 82 Table-6 Indoor radon levels in dwellings of Nandpur village (Uttar Pradesh) Radon Potential alpha Annual effective S.No. Type of room activity Activity (mWL) dose (mSv) (Bqm-^) 1. Bed room 11.4 93.7 3.8 2. Bed room 13.1 107.7 4.1 3. Living room 7.9 65.0 2.4 4. Kitchen 17.7 145.5 5.5 5. Living room 11.6 93.0 3.5 6. Kitchen 15.1 124.6 4.7 7. Bed room 13.5 110.3 4.2 8. Verandah 7.4 61.3 2.3 9. Bed room 16.2 133.3 5.1 10. Open space 8.5 69.9 2.7 11. Kitchen 19.6 161.2 6.1 12. Bed room 18.2 149.6 5.7 13. Living room 20.7 170.2 6.5 14. Living room 21.7 178.4 6.8 15. Verandah 11.5 94.6 3.6 16. Kitchen 24.1 198.2 7.5 17. Bed room 18.8 154.6 5.9 18. Kitchen 13.6 11.8 4.3 19. Bed room 18.5 135.7 5.2 20. Verandah 11.9 197.8 3.7 21. Living room 13.9 114.3 4.4 22. Bed room 22.1 181.7 6.9 23. Bed room 23.4 192.4 7.3 24. Living room 16.2 133.2 5.0 25. Pooja room 13.7 112.6 4.3 26. Kitchen 16.7 137.3 5.2 27. Open space 6.3 51.8 2.0 Average Value 15.2 125.2 4.8 S. D. 4.8 39.6 1.5 Rel. Std.% 31.6 31.6 31.3 83 TabIe-7 Indoor radon levels in dwellings of Silhari village (Uttar Pradesh) Potential alpha Annual Radon activity S.No. Type of room Activity effective dose (Bqm-') (mWL) (mSv) 1. Bed room 21.3 175.1 6.7 2. Living room 17.6 144.7 5.5 3. Verandah 11.2 96.2 3.7 4. Kitchen 24.3 224.5 7.6 5. Bed room 21.8 179.2 6.8 6. Living room 26.1 162.0 8.2 7. Bed room 26.3 175.9 8.2 8. Pooja room 16.1 132.4 5.0 9. Bed room 19.9 163.6 6.2 10. Kitchen 21.4 216.2 6.7 11. Bed room 15.7 129.1 4.9 12. Living room 15.0 123.2 4.7 13. Bed room 23.8 195.7 7.5 14. Kitchen 23:1 203.0 7.2 15. Living room 22.9 199.8 7.1 16. Pooja room 24.7 189.7 7.7 17. Bed room 18.3 150.5 5.7 18. Living room 27.3 188.3 8.6 19. Kitchen 19.7 214.6 6.2 20. Open space 5.2 42.8 1.6 Average Value 20.1 165.3 6.3 S.D. 5.3 43.7 1.7 Rel. Std. % 26.4 26.4 26.9 84 Table-8 Indoor radon levels in dwellings of Niwari village (Utter Pradesh) Annual Potential alpha Radon activity S.No. Type of room effective dose Activity (mWL) (Bqm^) (mSv) 1. Bed room 15.3 125.9 4.8 2. Kitchen 19.2 157.9 6.0 3. Living room 22.3 183.4 7.0 4. Bed room 20.1 165.3 6.3 5. Verandah 11.6 95.4 3.6 6. Kitchen 26.8 220.4 8.4 7. Pooja room 12.8 105.2 4.0 8. Open space 7.9 65.0 2.5 9. Living room 18.3 150.5 5.7 10. Kitchen 19.7 162.0 6.2 11. Open space 5.7 47.3 1.8 12. Bed room 15.8 129.9 4.9 13. Open space 2.7 71.5 0.8 14. Kitchen 17.4 143.1 5.4 15. Living room 21.1 173.5 6.6 16. Verandah 10.8 88.8 3.4 Average value 15.8 130.3 4.8 S.D. 5.7 46.5 1.8 Rel. Std.% 36.0 35.7 36.0 85 Table-9 Indoor radon levels in dwellings of Ramghat village (Utter Pradesh) Potential alpha Annual Radon activity S.No. Type of room Activity effective dose (Bqm-^) (mWL) (mSv) 1. Living room 13.6 111.8 4.2 2. Bed room 21.7 178.4 6.8 3. Kitchen 25.1 206.4 7.9 4. Bed room 18.3 150.5 5.7 5. Pooja room 17.5 143.9 5.5 6. Kitchen 20.1 165.3 6.3 7. Bed room 22.3 183.4 7.0 8. Bed room 16.9 139.0 5.3 9. Living room 12-.4 101.9 3.9 10. Kitchen 19.2 157.9 6.0 11. Bed room 17.0 139.7 5.3 12. Bed room 14.8 121.7 4.6 13. Living room 22.3 183.4 7.0 14. Bed room 15.8 129.9 4.9 15. Kitchen 24.9 204.7 7.8 16. Living room 21.7 178.4 6.8 17. Open space 7.2 59.5 2.2 Average Value 18.3 150.3 5.7 S. D. 4.5 37.4 1.4 Rel. Std. % 24.6 24.9 24.7 86 3.6.4 Study of radon and its daughters in dwellings of Bhatinda near a thermal power plant (Punjab), India Burning of coal is one of the sources for technologically enhanced exposure of human beings from natural radio-nuclides. The population is exposed to radiation which is discharged to the environment by the emissions from thermal power stations in gaseous and particulate forms containing radioisotopes. Measurements of indoor radon oncentration in about 33 rooms of different dwellings in Bhatinda (Punjab) near a thermal power plant were carried out to assess the variability of expected exposure of the population to radon and its progeny. Table-10 presents the measurements made for radon concentrations in terms of working Level and activity in Bqm"^ in the dwellings of Bhatinda near a thermal power plant. The inhalation dose to the lung tissues in terms of effective dose equivalents. The measured radon concentration varies from 69.9 Bqm''^ to 135.7 Bqm"' in bed rooms; from 76.8 to 144.7 Bqm'^ in living rooms; from 51.8 to 65.0 Bqm'^ in varandas; from 87.5 to 147.6 Bqm'^ in bathrooms and from 139.7 to 224.5 in kitchens. Kitchens show the maximum radon concentration. This may be due to the contribution of radon from fuels (gas. kerosene etc.) and water. Varanda is fairly ventilated and thus gives minimum value of radon. Axmual effective dose equivalents received by the inhalation of radon progeny are found to vary from 2.0 to 8.6 mSv. According to the recommendation of ICRP, it is observed that the radon levels in the dwellings of Bhatinda near thermal power plant are in the action level limit. 87 Table-10 Indoor radon levels in dwellings of Bhatinda (Pb.) near a thermal power plant Potential of S. No. of the Radon Activity Annual Types of room Alpha Activity dwelling ( Bqm ^) effective (mSv) (mWL) l.(a) Living room 13.4 110.3 4.2 (b) Bed room 15.1 124.6 4.7 (c) Kitchen 24.1 198.2 7.5 (d) Varanda 7.9 65.0 2.4 2. (a) Bed room 12.4 101.9 3.9 (b) Kitchen 17.0 139.7 5.3 (c) Living room 15.8 129.9 4.9 (d) Bed room 11.6 95.4 3.6 (e) Living room 10.8 88.8 3.4 3. (a) Bed room 10.4 85.0 3.2 (b) Living room 14.5 119.0 4.5 (c) Kitchen 27.3 224.5 8.6 (d) Bed room 11.0 90.8 3.5 4. (a) Bath room 11.6 93.0 3.5 (b) Living room 16.2 133.3 5.1 (c) Kitchen 26.3 216.2 8.2 (d) Bed room 8.5 69.9 2.7 5. (a) Bed room 16.5 135.7 5.2 (b) Living room 17.6 144.7 5.5 (c) Kitchen 24.1 198.2 7.5 (d) Bath room 13.9 114.3 4.4 (e) Bed room 16.2 133.2 5.0 6. (a) Living room 10.4 85.8 3.2 (b) Bath room 10.6 87.5 3.3 (c) Bed room 12.2 100.6 3.8 (d) Varanda 6.3 51.8 2.0 (e) Kitchen 25.3 208.3 7.9 7. (a) Bed room 13.7 112.6 4.3 (b) Kitchen 20.8 171.1 6.5 (c) Living room 9.3 76.8 2.9 8. (a) Bath room 17.9 147.6 5.6 (b) Kitchen 22.2 182.3 6.9 (0 Living room 13.1 107.7 4.1 Average Value 15.3 120.9 4.8 S.D. 5.5 48.2 1.7 Rel.Std.% 36.0 39.7 36.1 • 88 3.6.5 Indoor radon monitoring in some buildings surrounding the National Hydroelectric Power Corporation (NHPC) Project at Upper Siang in Arunachal Pradesh, India In the present study measurements of radon concentration in the rooms of some buildings surrounding the National Hydroelectric Power Corporation (NHPC) project at upper Siang in Arunachal Pradesh, India shown in Figure 1, are carried out before its operation and to compare the results with those to be obtained after its operation This 11,000 MW Project is situated at Upper Siang, the hilly region of Arunachal Pradesh and is country's largest power project and the world's third largest Stui^' Area District map of Arunachai Pradesh Figure-l. Map showing the location of National Hydroelectric Power Corporation (NHPC) Project at Upper Siang in Arunachal Pradesh, India 89 Table 11 presents the radon levels in the rooms of buildings situated in the surroundings of NHPC project at Upper Siang in Arunachal Pradesh, India. The radon levels in these rooms are found to vary from 9 to 472 Bq m'^ with an average value of 158 Bq m"''. Annual effective dose varies from 0.1 to 7.0 mSv y'' with an average value of 2.3 mSv y'V There is large variation in the values obtained, depending on the location and ventilation conditions. Radon concentration is minimum in hostels and office rooms. As being the hilly area the variation may be due to the location and also due to ventilation conditions. The values are well within the action levels proposed by ICRP. Pre-Operation data will be interesting and important for comparison with the post operation data to investigate the effect of water accumulation on the radon levels in the dwellings. 90 Table-11 Indoor radon levels in the rooms of some buildings surrounding the National Hydroelectric Power Corporation (NHPC) project at upper Siang in Arunachai Pradesh, India Potential Alpha Radon Energy Annual effective dose S.No. Location activity Concentration (mSv) (Bqm-^) (mWL) 1. Office of P/A wing-1 . 40±3 370 ± 26 5.7 ±0.4 2. Office of P/A wing-2 18±2 167 ±17 2.6 ±0.3 3. Office Geology 19±2 176±18 2.6 ±0.3 Department. 4. Storeroom 28 ±2 259 ±21 4.0 ±0.3 5. Office of the store 17±2 157±16 2.6 ±0.3 wing 6. Office of P/A Dept. 21±2 194 ±17 3.1 ±0.3 room-1 7. Office of P/A Dept. 51±3 472 ± 28 7.0 ±0.4 room-2 8. Hostel room -1 30 ±2 278 ± 19 4.0 ± 0.3 9. Hostel room -2 5±1 46 ±9 0.9 ±0.2 10. Hostel room -3 6±1 56 ±10 0.9 ±0.2 11. Hostel room -4 5±1 46 ±9 0.9 ±0.2 12. Wireless room • 11±1 102 ± 13 1.8 ±0.2 13. Kitchen 13 ±1 120 ±12 1.8 ±0.2 14. Office complex-1 4 ±0.3 37 ±3 0.4 ± .04 15. Office complex -2 7±1 65 ±9 0.9 ±0.1 16. Survey Dept 7±1 65 ±9 0.9 ±0.1 17. Takkan Texan House 10±1 93 ±12 1.3 ±0.2 18. Field Hostel Room 15±2 139±15 2.2 ±0.3 19. Erring Area 18±2 167±17 2.6 ±0.3 20. DFO Office 31±3 287 ±23 4.4 ±0.3 21. V.I.T Coloney 6±1 56 ±10 0.9 ±0.1 22. Seminar hall 38 ±3 352 ±25 5.3 ±0.3 23. Seminar Hall office 1±0.5 9±4 0.1 ±.04 24. Hostel room -5 19±2 176±18 0.3 ±0.04 25. Hostel room -6 11±1 102 ± 13 1.8 ±0.2 26. Non Exchange • 13±2 120 ±14 1.8 ±0.2 Average Value 16.6 ±1.6 158 ± 14.9 2.3 ± 0.2 S.D. 12.6 ±0.8 114 ±6.2 1.8 ±0.1 Rel. Std% 75.9 ±49.4 72.2 ±41.6 78.3 ± 50 91 3.6.6 Indoor radon monitoring and effective dose measurement in some dwellings of Gujarat Kutch district of Gujrat state was severely jolted by a powerful earthquake on the morning of January 26, 2001. The earthquake took a tool of 20,072 human lives, killed 21551 cattle and inflicted various grades of damage to about 10.8 lakh houses in 7904 villages. LR-115 Type II Solid State Nuclear Track Detectors (SSNTD's) in bare mode have been used to measure the radon concentration in dwellings of Kutch (Bhuj) region of Gujarat state India. Annual effective dose has been calculated from the radon concentration to carry out the assessment of the variability of expected radon exposure of the population due to radon and its progeny. Table 12 presents the measured vlaues of radon levels in dwellings of Kutch (Gujarat). The measured radon concentration varies from 137.3 Bqm'^ to 328.8 Bqm'^ in bed rooms; from 141.6 to 338.2 Bqm''' in drawing rooms; from 174.1 to 241.1 Bqm"^ in office; from 144.3 to 274.5 Bqm'^ in bathrooms and from 210.9 to 455.4 in kitchens. Annual effective dose equivalents received by the inhalation of radon progeny varies from 4.6 to 15.4 mSv with an average of 7.7 mSv. The radon levels in the indoor atmosphere (bed rooms, drawing rooms, Kitchen, office and bath rooms) are much higher than in (open space) of the dwellings. Kitchens show the maximum radon concentration this may be due to the contribution of radon from fuels (gas, kerosene etc.) and water. The measured values are below the recommended action levels. 92 Table-12 Indoor radon levels in dwellings of Kutch (Gujarat) Potential alpha Radon Annual energy S.No. Location activity effective dose concentration (Bqm*) (mSv) (mWL) 1. Bed room( Bhuj -Kutch) 16.65 154.0 5.2 2. Bed room( Bhuj -Kutch) 18.85 174.5 5.9 3. Bed room( Bhuj -Kutch) 16.0 148.0 5.0 4. Bed room( Bhuj -Kutch) 14.8 137.3 4.6 5. Bed room( Kodic Bhuj -Kutch) 35.5 328.8 11.1 6. Bed rooni( Mirjapur Bhuj - Kutch) 31.3 289.6 9.8 7. Bed room( Mirjapur Bhuj -Kutch) 23.5 217.6 7.4 8. Bed room( Mirjapur Bhuj -Kutch) 28.2 261.2 8.8 9. Bed room( Bhuj -Kutch) 21.1 194.9 6.6 10 Bed room( Bhuj -Kutch) 31.5 291.3 9.7 11. Bed rooin( Bhuj -Kutch) 17.7 164.1 5.5 12. Bed room( Bhuj -Kutch) 20.3 187.5 6.3 13. Bed room( Bhuj -Kutch) 23.2 214.3 7.3 14. Bed room(Mundra -2 Kutch) 26.4 244.4 8.3 15. Bed room (Mundra -2 Kutch) 27.2 251.5 8.5 16. Bed room (Mundra -2 Kutch) 18.85 174.4 5.9 17. Bed room (Mundra -2 Kutch) 22.2 204.9 6.9 18. Bed room (Addera - Kutch) 26.2 242.7 8.2 19. Bed room (Addera - Kutch) 25.0 231.0 7.8 20. Bed room (Nalia - Kutch) 27.9 257.8 8.7 21. Bed room (Nalia - Kutch) 21.0 194.2 6.6 22. Drawing room (Bhuj -Kutch) 17.2 159.0 5.4 23. Drawing room (Bhuj -Kutch) 15.31 141.6 4.8 24. Drawing room (Bhuj -Kutch) 15.4 142.3 4.8 25. Drawing room (Bhuj -Kutch) 23.6 218.3 7.4 26. Drawing room (Bhuj -Kutch) 36.6 338.2 11.5 27. Drawing room (Bhuj -Kutch) 24.3 224.3 7.6 1 28. Drawing room (Bhuj -Kutch) 19.5 180.8 6.1 29. Drawing room (Bhuj -Kutch) 20.6 190.9 6.4 30. Drawing room (Bhuj -Kutch) 25.8 238.7 8.1 31. Drawing room (Bhuj -Kutch) 23.2 214.3 7.3 32. Drawing room (Bhuj -Kutch) 23.9 220.9 7.5 33. Drawing room (Bhuj -Kutch) 27.9 257.8 8.7 34. Drawing room (Bhuj -Kutch) 20.3 190.8 6.5 j 35. Drawing room (Bhuj -Kutch) 26.8 247.7 8.4 36. Drawing room (Bhuj -Kutch) 21.9 202.6 6.9 93 Continued 37. Drawing room (Bhuj -Kutch) 32.1 296.7 10.0 38. Drawing room (Bhuj -Kutch) 30.0 277.9 9.4 39. Kitchen (Bhuj-Kutch) 38.6 356.6 12.1 40. Kitchen (Bhuj-Kutch) 30.0 277.9 9.4 41. Kitchen (Bhuj-Kutch) 26.1 241.1 8.2 42. Kitchen (Bhuj-Kutch) 37.6 348.2 11.8 43. Kitchen (Bhuj-Kutch) 25.3 234.4 7.9 44. Kitchen (Bhuj-Kutch) 23.7 218.9 7.4 45. Kitchen (Bhuj-Kutch) 22.8 210.9 7.1 46. Kitchen (Bhuj-Kutch) 32.9 304.7 10.3 47. Kitchen (Bhuj-Kutch) 32.3 299.0 10.1 48. Kitchen (Bhuj-Kutch) 49.2 455.4 15.4 49. Office (Bhuj-Kutch) 18.8 174.1 5.9 50.. Office (Bhuj-Kutch) 26.1 241.1 8.2 51. Office (Bhuj-Kutch) 24.6 227.7 7.7 52. Office (Bhuj-Kutch) 22.4 207.6 7.0 53. Office (Bhuj-Kutch) 21.4 197.5 6.7 54. Office (Bhuj-Kutch) 19.2 177.4 6.0 55. Bathroom (Bhuj-Kutch) 15.6 144.3 4.9 56. Bathroom (Bhuj-Kutch) 18.9 174.8 5.9 57. Bathroom (Bhuj-Kutch) 22.4 207.6 7.0 58. Bathroom ( Bhuj-Kutch) 16.4 151.3 5.1 59. Bathroom ( Bhuj-Kutch) 29.7 274.5 9.3 60. Toilet (Bhuj-Kutch) 26.1 241.1 8.2 i 94 3.6.7 Radon monitoring in the dwellings of Jharkhand State India Jharkhand state of India is rich in minerals and is called the store house of minerals. In addition to uranium deposits at Jaduguda, there are huge deposits of bauxite, mica and coal along with iron, copper, chromites, tungsten, lime stone, feldspar and quartz etc.The soil in the Jharkhand state of India contains marginally elevated levels of natural radioactivity due to presence of higher mineralization of uranium. The houses of the local population in this region are built using local soil and building materials. Further more, uranium mining and ore processing are also carried out in this region. Therefore, to assess the contribution of elevated natural milling processes on the local environment, a survey was carried out to evaluate indoor radon and effective doses levels in some of the dwellings in different place. The selections of houses were done on their type of construction and building material used. The results are presented in Table 12. The measured radon concentration varies from 107.1 Bqm'^ to 257.8 Bqm'^ in bed rooms; from 110.5 to 219.3 Bqm'^ in drawing rooms; from 145.6 to 170.7 Bqm"^ in store room and from 169.1 Bqm'^ to 368.9 Bqm'^ in kitchens in these dwellings whereas the annual effective dose varies from 4.6 to 15.4 mSv with an average value of 7.7 mSv. Radon concentrations in these dwellings differ from place to place due to differences in geology and climate and in building construction materials. Although exposure to radon is in tropical climates is unlikely to be of serious concern, keeping in view the radiological significance of radon level in different parts of the country it is helpful in defining the radon prone areas. 95 Table-12 Indoor radon levels in some dwellings of Jharkhand State, India Annual effective Potential alpha Radon activity S.No. Location energy concentration dose (Bqm') (mWL) (mSv) 1. Bed room 14.9 137.9 4.7 2. Bed room 16.7 154.0 5.2 3. Bed room 22.4 207.6 7.0 4. Bed room 14.5 133.9 4.5 5. Bed room 18.8 174.1 5.9 6. Bed room 13.4 123.9 4.2 7. Bed room 16.3 150.7 5.1 8. Bed room 18.8 174.1 5.9 9. Bed room 21.0 194.2 6.6 10 Bed room 13.4 123.9 4.2 11. Bed room 11.6 107.1 3.6 12. Bed room 15.9 147.3 4.9 13. Bed room 17.7 164.1 5.5 14. Bed room 17.0 157.4 5.3 15. Bed room 15.3 141.3 4.8 16. Bed room 21.7 200.9 6.8 17. Bed room 22.1 204.2 6.9 18. Bed room 20.8 192.5 6.5 19. Bed room 15.6 143.9 4.9 20. Bed room 20.3 187.5 6.3 21. Bed room 21.4 197.5 6.7 22. Bed room 17.0 157.4 5.3 23. Bed room 20.1 185.8 6.3 24. Bed room 18.8 174.1 5.9 25. Bed room 20.8 192.5 6.5 26. Bed room 25.3 234.4 7.9 27. Bed room 27.9 257.8 8.7 28. Bed room 23.5 217.6 7.4 29. Bed room 18.3 169.4 5.7 30. Drawing room 16.3 150.7 5.1 31. Drawing room 23.7 219.3 ^•^ 32. Drawing room 15.2 140.6 4.7 33. Drawing room 17.7 164.1 5.5 34. Drawing room 13.8 127.2 4.3 35. Drawing room 14.9 137.9 4.7 36. Drawing room 11.9 110.5 3.7 37. Drawing room 17.8 164.7 5.6 38. 1 Drawing room 16.7 154.0 5.2 39. Kitchen 28.2 261.2 8.8 96 40. Kitchen 39.9 368.9 12.5 41. Kitchen 22.5 207.9 7.0 42. Kitchen 31.6 294.6 9.9 43. Kitchen 25.3 234.4 7.4 44. Kitchen 26.1 241.1 8.1 45. Kitchen 22.7 209.8 7.1 46. Kitchen 22.4 207.6 7.0 47. Kitchen 19.5 180.8 6.1 48. Kitchen 25.0 231.0 7.8 49. Kitchen 20.6 190.8 6.5 50.. Kitchen 27.1 251.1 5.7 51. Kitchen 18.3 169.1 4.9 52. Kitchen 26.1 241.1 8.2 53. Kitchen 26.2 242.8 8.2 54. Kitchen 31.9 294.6 9.9 55. Kitchen 30.0 277.9 9.4 56. Kitchen 29.7 274.5 9.3 57. Kitchen 34.8 322.1 10.9 58. Storeroom 18.5 170.7 5.8 59. Storeroom 15.7 145.6 4.9 60. Office room 11.6 107.1 3.6 97 3.7.1 Indoor radon, thoron and their progeny in some Indian dwellings of U. P., India using twin chamber dosimeter cups with SSNTDs Concentration of radon-thoron and their progeny levels in the dwellings under investigation were measured using the twin chamber Solid State Nuclear Track Detector (SSNTD) based dosimeters using 12|im thick, LR-115 type II pelicuUable. cellulose nitrate based SSNTDs manufactured by Kodak Pathe, France. The dosimeter has been developed at Bhabha Atomic Research Centre (BARC) and is shown in Figure-2. 3 Bare Mode 4^ 1 2 Membrane Filter Glass Fiber Filter M F Radon-Thoron Radon Compartment Compartment II Figure-2. Radon- Thoron twin chamber dosimeter cup system 98 Each cylindrical chamber has a height of 4.1 cm and a radius of 3.1 cm. One piece of the detector film (SSNTD) of size 2cm x 2 cm. placed in compartment M measures radon only which diffuses into it from the ambient air through a semi-permeable Q 7 9 membrane of 25 urn thickness having diffusion coefficient in the range of 10" to 10' cm s"'(Eappen and Mayya, 2004). It allows the build up of about 90% of radon gas in the compartment and suppresses thoron gas concentration by more than 99%. The mean time for radon to reach the steady- state concentration inside the cup is about 4.5 hour. Glass fiber filter paper of thickness of 0.56 mm in the compartment F allows both radon and thoron gases to diffuse in and hence the tracks on second piece of the detector film placed in this chamber are related to the concentrations of both the gases. Third piece of the detector film exposed in bare mode (placed on the outer surface of the dosimeter) registers alpha tracks attributed to both the gases and their alpha-emitting progeny, namely ^^^Po ^''*Po, ^'^Po, and ^'^Po. LR-115 detectors do not develop tracks originating from the progeny alphas, deposited on them (Mayya et al., 1998; Nikolaev and Ilic, 1999; Durrani, 1997) and, therefore, are ideally suited for radioactive gas concentration study. Twin chamber dosimeter cups fitted with LR-115 type 11 films were placed in different dwellings and exposed for 100 days. After exposure the films were etched in 2.5 NaOH solution at 60°C for 90 min in a constant temperature water bath. The etching processes removes a bulk thickness of 4^m leaving a residual detector for thickness of 8)im. The detectors are pre-sparked using spark counter (Cross and Tommasino, 1970) at a voltage of 900 V to fully develop the partially etched track holes. The tracks are then counted at the voltage corresponding to the plateau region of the counter (450 V). The concentrations are derived from the observed track densities using appropriate calibration factors. The calibration factors depend upon various parameters such as membrane and filter characteristics as well as the energy of the alpha particles for the cup mode exposure, the parameters of the etching process and spark counting characteristics. In the present work an effort has been made to make indoor radon/thoron measurements in the dwellings of some cities in our region of India surrounded by a thermal power plant and industrial belt by using SSNTD,s in Plastic Twin Chamber Dosimeter cups. In Kasimpur a big coal fired thermal power plant is operational. After burning of coal which contains higher levels of uranium (Jojo et el, 1993) the subsequent emission 99 to the environment can cause enhancement in the ambient radiation levels. Investigations were carried out in the dwellings around the thermal power plant. For comparison of ambient radon levels a similar study was also carried out at Aligarh which is a city near Kasimpur thermal power Plant. Khurja is a centre of ceramic industry having about 500 potteries in small scale sector. City of Bulandshahr situated only 15 km from Khurja. Ghaziabad is an industrial area and about 50 km away from Khurja and very close to New Delhi, capital of India. From track density concentration of radon (CR) and thoron (Cj) were calculated using the sensitivity factor determined from the controlled experiments (Mayya et al., 1998; Sannapa et al., 2003; Sonkawade et al; 2005): ^'^*^'" > = 1^, (2) Where, CR = Radon concentration CT = Thoron concentration Tm = Track density in membrane compartment Tf = track density in filter compartment d = Exposure time Sensitivity factor for membrane compartment (Sm) = 0.019±0.003 Trc m'^ d''/Bq m'' Sensitivity factor for radon in filter compartments (Srf) = 0.020±0.004 Trc m'^ d''/Bq m'^ Sensitivity factor for thoron in filter compartment (Stf) = 0.016±0.005 Trc m''^ d"'/Bq m"'' The inhalation dose (D) in mSv y'' was estimated using the relation: D= {0.17+9FR)CR+(0.11+32FT)CT ^7000 X 10-^ (3) Where FR and FT are equilibrium factor for radon and thoron respectively. The values are taken as 0.4 and 0.1 for radon and thoron (UNSCEAR, 2000). 100 The radon and thoron daughter concentrations were calculated in terms of Potential Alpha Energy Concentration (PAEC) in mWL. From the bare track density which is related to the concentration of both the gases and their daughters and radon and thoron concentrations. The life time fatality risks were also calculated from the values obtained for radon and thoron and their daughter concentrations in terms of Potential Alpha Energy Concentration (PAEC) in mWL extracted from bare detector exposure. Measured radon/thoron concentrations were converted into equilibrium equivalent concentration (EEC), which was further converted into Potential Alpha Energy Concentration (PAEC) using the relation: CR or CT = PAEC (WL) x 3700/F (4) Here, F is the equilibrium factor. PAEC was converted into annual effective dose by using dose conversion factors. Radon daughter dose conversion factor for the population is given as 3.9 mSv per WLM whereas the effective dose equivalent for thoron is 3.4 mSv per WLM (ICRP, 1993). Using these conversion factors PAEC was converted into annual effective dose. The values of radon, thoron and their daughters concentrations and inhalation dose obtained by using relations 1, 2 ,3 and 4 are presented in Table-13 and 14. Table-13 Radon and Thoron concentration and inhalation dose in dwellings of cities of U.P. state of India Location Tm( Tr cm'^) Tf(Trcm-') CR(Bqm-') CrCBqm-') D (Inhalation dose) (mSv y"') 42.6 49 22.4 ±3.4 2.6 ±0.4 0.651 40 49 31.1±3.3 4.3 ±0.6 0.656 Kasimpur 24 56 12.6 ±2.6 19.3 ±2.6 0.779 13.6 19 7.2 ±1.9 2.9 ±0.7 0.257 13 29.6 6.8 ±1.8 10.0 ±1.8 0.392 29 50 15.3 ±2.8 12.1 ±1.7 0.648 43 74.5 22.6± 3.4 18.3 ±2.1 1.020 Aligarh 20 37.6 10.5 ±2.3 10.4 ±1.7 0.240 33 36.6 17.4 ±3.0 1.1 ±0.2 0.484 5.3 55.6 2.8 ± 1.2 33.3 ±4.5 0.845 46 64.3 24.2 ±3.6 9.9 ±1.2 0.868 6.6 9.6 3.5 ±1.4 1.6±0.5 0.129 8 30 4.2 ±1.5 13.5 ±2.5 0.423 Khurja 39 •54 20.5 ±3.3 8.1 ± 1.1 0.728 33 44 17.4 ±3.0 5.6 ±0.8 0.588 54 78 28.4 ±3.7 13.3 ±1.5 1.050 63 81.5 33.2 ±4.2 9.4 ± 1.0 1.090 27 41.7 14.2 ±2.7 8.3+1.3 0.567 Bulandshahr 37.3 71.3 19.6 ±3.2 20.1±2.4 0.982 42 65 22.1 ±3.4 13.0± 1.6 0.884 56.33 74.3 29.6 ±3.9 9.4±1.1 0.998 11.1 35 5.8 ±1.7 14.6 ±2.5 0.491 14 32 7.3 ±1.9 10.9± 1.9 0.445 22.6 48.7 11.9 ±2.5 15.5 ±2.2 0.673 Ghaziabad 29.66 37 15.6 ±2.9 3.6 ±0.6 0.495 25 64.3 13.5 ±2.7 23.3 ±2.9 0.896 58.66 .120 30.8 ±4.0 36.5 ±3.3 1.650 53.66 67 28.2 ±3.8 6.5 ±0.8 0.894 70 95 36.8 ±4.4 13.4±1.6 1.280 Minimum - 5.3 9.6 2.8±1.2 1.1 ±0.2 0.129 Maximum 70.0 120 36.8 ± 4.4 36.5 ± 3.3 1.650 Average Value 33.1 54.1 17.8±2.9 12.1 ± 1.6 0.730 S.D. % 17.7 23.1 9.6 ±0.9 8.3 ±1.0 0.320 102 Table-14 Radon and thoron daughters, annual exposure (WLM), life time fatality risk factor in dwellings of U.P. Location Radon Thoron Daughters Annual Exposure Lifetime fatality risk Daughters ( (mWL) (Radon + factor X 10"^ mWL) Thoron) WLM 2.42 ± 0.37 0.07 ±0.01 0.090 0.27 2.28 ± 0.36 0.12 ±0.02 0.084 0.25 Kasimpur 1.36 ±0.28 0.52 ±0.07 0.070 0.21 0.78 ±0.21 0.08 ± 0.02 0.032 0.09 0.74 ± 0.20 0.27 ± 0.05 0.028 0.84 1.65 ±0.30 0.32 ± 0.04 0.07 0.21 2.44 ± 0.37 0.49 ± 0.05 0.11 0.33 Aligarh 1.14±0.14 0.28 ± 0.05 0.05 0.15 1.88 ±0.32 0.03 ± 0.01 0.07 0.21 0.30±0.13 0.09 ±0.12 0.04 0.12 2.61 ±0.39 0.12±0.12 0.09 0.27 0.38 ±0.15 0.04 ±0.01 0.01 0.03 0.45 ±0.16 0.36 ± 0.07 0.03 0.09 Khurja 2.21 ±0.36 0.22 ± 0.03 0.09 0.26 1.88 ±0.32 0.15 ±0.02 0.07 0.22 3.07 ±0.40 0.36 ±0.04 0.12 0.37 3.58 ±0.45 0.25 ±0.03 0.05 0.14 , 1.53 ±0.29 0.22 ± 0.03 0.063 0.19 ! Bulandshahr 2.11 ±0.34 0.54 ±0.06 0.095 0.06 2.39 ±0.37 0.35 ± 0.04 0.098 0.29 3.20 ±0.42 0.25 ± 0.03 0.124 0.37 0.63 ±0.18 0.39 ±0.07 0.036 0.108 0.78 ± 0.20 0.29 ±0.25 0.038 0.114 1.3 ±0.27 0.42 ± 0.06 0.183 Ghaziabad 0.061 1.7±0.31 0.10 ±0.02 0.064 0.192 1.5 ±0.30 0.62 ± 0.07 0.076 0.228 3.3 ±0.43 0.98 ± 0.09 0.158 0.474 3.0 ±0.40 0.17 ±0.02 0.115 0.345 3.97 ±0.47 0.09 ±0.01 0.146 0.438 Minimum 0.30±0.13 0.03 ±0.01 0.010 0.03 X 10"' Maximum 3.97 ±0.47 0.98 ± 0.09 0.158 0.474X IQ-' I Average Value 1.88 ±0.31 0.28 ±0.05 0.075 0.243 xlO"' S.D.% 1.00 ±0.09 0.20 ±0.04 0.03 0.156 xlO"* 103 The results of the measured radon/thoron and inhalation dose in the dwellings of the cities of Kasimpur, Aligarh, Khurja, Bulandshahr and Ghaziabad situated in the state of Uttar Pradesh, India is presented in table-13 indicate that radon concentrations vary fi-om 2.8 ± 1.2 Bq m"^ to 36.8 ± 4.4 Bq m'^ with an average value 17.8 ± 2.9 Bq m"\ whereas thoron concentrations vary from 1.1 ±0.2 Bq m'^ to 36.5 ± 3.3 Bq m'^ with an average value of 12.1 ± 1.6 Bq m"^. Inhalation dose is found to vary from 0.129 to 1.65 mSv y'' with an average value of 0.730 mSv y''. From the results of table-14 it can be observed that radon and thoron PAEC values vary from 0.30 ± 0.13 mWL to 3.97 ± 0.47 mWL and 0.03 ± 0.01 mWL to 0.98 ± 0.09 mWL respectively. The life time fatality risk factor varies from 0.03 x lO"^ to 0.47 x 10"^ As expected in the normal background area thoron and its daughters contribute a little towards the radiation dose. House wise analyses of radon and thoron and their daughters concentrations (Bq m") show a wide variation in all the cities. This wide variation in the concentration of both radon and thoron and their daughters may be attributed to the variation in primordial radioactivity in the soil and building materials. There is not much variation in radon/thoron concentrations except in industrial town, Ghaziabad which shows higher values. These may be due to the industrial waste used as building material. The cities in which the measurements have been carried out the dwellings around the thermal power plant, potteries and an industrial area lie in the normal back ground region of India near by the New Delhi capital of India. The inhalation dose, radon and thoron concentrations are within the permissible limits. 3.7.2 Study of indoor radon/thoron in some dwellings surrounding Narora Atomic Power Station (NAPS) using twin ciiamber dosimeter cups Solid State Nuclear Track Detectors (SSNTD's) based twin chamber dosimeters were used for estimating radon ("^^Rn) and thoron (^^°Rn) gases and their progeny concentrations in the dwellings surrounding the Narora Atomic Power Station (NAPS). The values obtained for radon and thoron concentrations and inhalation dose are presented in Tables-15 & 16. 104 Radon concentrations are found to vary from 11.2 ± 2.4 Bqm'^ to 54.5 ± 5.4.Bqm^, whereas thoron concentrations are small as expected in normal background region and vary from 0.13 ± 0.2 Bqm"'' to 70.6 ± 5.3 Bqm'^ respectively. Inhalation dose (D) varies from 0.60 to 2.46 mSv y'. The life time fatality risks were calculated from the values obtained for radon and thoron and their daughters concentrations in terms of Potential Alpha Energy Concentration (PAEC) in mWL extracted from bare detector exposure. Radon and thoron PAEC values are found to vary from 1.21 ± 0.26 mWL to 5.88 ± 0.58 mWL and 0.003 ± 0.0 mWL to 1.90 ± 0.14 mWL respectively. Radon daughter dose conversion factor for the population is given as 3.9 mSv per WLM whereas the effective dose equivalent for thoron is 3.4 mSv per WLM (ICRP, 1981). Using these conversion factors PAEC was converted into annual effective dose. The life time risk associated with the exposure due to indoor radon and its progeny was computed by using IWLM = 10x10"^ case/year. If the risk persists for 30 years, lifetime fatality risk is 3x10"^ case/WLM (ICRP, 1981). The lifetime fatality risk factor was also estimated and varies from 0.15 X 10"^ to 0.69 x lO*^. The inhalation dose, radon and thoron concentrations are also within the permissible limits. 105 Table-15 Radon and Thoron concentration and inhalation dose in dwellings surrounding Narora Atomic Power Station Place Tf CR CT D (Tr.cm-^) (Tr.cm-^) (Bq. m'^) (Bq. m"^) Inhalation dose (mSvy-') House no.-1 51.3 87.0 27.0 ± 3.8 20.6 ±2.2 1.19 Hoxise no.-2 76.6 111.6 40.3 ±4.6 19.4 ±1.8 1.51 House no.-3 103.6 144.6 54.5 ± 5.4 22.3 ±1.9 1.95 House no.-4 44.6 47.0 23.4 ±3.5 0.13 ±0.02 0.62 House no.-5 88.0 149.6 46.3 ± 4.9 35.6 ±2.9 2.05 House no.-6 25.6 70.6 13.5 ±2.6 27.3 ± 3.2 0.98 House no.-7 60.3 176.3 31.7±4.1 70.6 ±5.3 2.46 House no.-8 26.0 80.6 13.7 ±2.6 33.3 ±3.7 1.13 House no.-9 21.3 43.6 11.2 ±2.4 13.3 ±2.0 0.60 House no.-10 36.6 67.3 19.3 ±3.2 18.0 ±2.2 0.93 Table-16 Radon and thoron daughters, annual exposure (WLM), life time fatality risk factor in dwellings surrounding Narora Atomic Power Station Place Radon Thoron Annual Lifetime Effective dose Daughters Daughters Exposure fatality risk (mSvy') (mWL) (mWL) (Radon + factor X 10"^ Thoron) WLM House no.-1 2.92 ±0.41 0.56 ± 0.06 0.13 0.39 0.48 House no.-2 4.36 ±0.50 0.52 ± 0.05 0.18 0.54 0.67 House no.-3 5.88 ±0.58 0.60 ± 0.05 0.23 0.69 0.90 House no.-4 2.53 ± 0.38 0.003 ± 0.0 0.09 0.27 0.35 House no.-5 5.01 ± 0.53 0.96 ± 0.08 0.21 0.63 0.82 House no.-6 1.46 ±0.29 0.73 ± 0.09 0.08 0.24 0.29 House no.-7 3.43 ± 0.44 1.90 ±0.14 0.19 0.57 0.71 House no.-8 1.48 ±0.29 0.90 ±0.10 0.08 0.24 0.32 House no.-9 1.21 ±0.26 0.36 ± 0.50 0.05 0.15 0.21 House no.-10 2.09 ±0.35 0.49 ± 0.6 0.09 0.27 0.35 106 References BEIR VI (Report on the Biological effects of Ionizing Radiation), 1999. 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Nikolaev, V.A., Ilic.R., 1999. Etched track radiometers in radon measurements: a review. Radiat. Meas.30,1-13. 108 Radiation protection against radon in workplaces other than mines. Vienna : International Atomic Energy Agency, 2003. Safety reports series, ISSN 1020-6450 ; no. 33 Ramola, R.C., Singh, M., Virk, H.S. 1987. Measurement of indoor radon concentration using LR-115 plastic track detectors. Ind. J. Pure & AppL.Phys. 25,127-129. Samet. J. M., Pathak, D. R., Morgan", M.V., Marbury, M. C, Key, C. R., Valdivia A.A. 1989. Radon progeny exposure and lung cancer risk in new Mexico uranium mines. Health Physics., 56,415-421. Sannapa, J., Chandrashekara M.S., Sathish, L.A., Paramesh L., Venkataramaih P., 2003. Study of back ground radiation dose in Mysore city, Kamatka State, India: Radiat. Meas. 37, 55-65. Sevc, J., Kunz, E, Placek. V., 1976. Lung cancer in uranium miners and long term exposure to radon daughter products. Health Phys., 30,433-437. Singh, A.K., Khan, A.J., Prasad, R., 1997. Distribution of radon levels in Indian dwellings. Radiat. Prot. Dosim. 74,189-192 Singh, A.K., Khan, A.J., Prasad, R., 1999. Study of radon concentration in some dwellings of Rajasthan. Health Phys. 76,306-310. Sonkawade, R.G., Ramola, R.C. Kant, K., Kanjilal D.K., Dhiaryawan M.P., Gupta, P., 2005. Dosimetry in the environment of 15 UD pelletron accelerator using plastic track detectors. Bulletin of Radiat. Protect. 28 (1-4) 156-159. Steinhauser, F., Hofinan, W., and Lettner, H., 1994. Thoron exposure to manz a negligible issue. Radiat. Prot.Dosim.56. 1-44. Swedjemark, G. A. and Mjones, L. Radon and Radon Daughter Concentrations in Swidesh Homes . 1984. Radiat. Prot. Dosim. 7, 341-345 UNSCEAR, 1993.United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and Effects of Ionizing Radiation. United Nations, New York. UNSCEAR, 2000.Umted Nations Scientific Committee on the Effects of Atomic Radiation: Sources and Effects of Ionizing Radiation, Vol.1.United Nations, New York. Virk, H.S., Sharma, N., 1998. Indoor radon levels in the radioactive areas of Himachal Pradesh: an inter-comparison of active and passive techniques. Ind. J. Rad. Prot. Environ. 21(2): 103-106. 109 CHAPTER -4 MEASUREMENT OF NMIAL fflONDOESINSOLffi AND BUDIG Chapter -IV 4.1 Introduction The knowledge of radionuclides distribution and radiation levels in the environment is important for assessing the effects of radiation exposure to human beings due to both terrestrial and extra terrestrial sources. Terrestrial radiation is due to the radionuclides present in different amounts in rocks, soils, building materials, water and atmosphere. Some of the radionuclides from these sources may be transferred to human beings through food chain or inhalation. The exposure of human beings to ionizing radiations takes place due to naturally occurring radioactive elements in the solids and rocks, cosmic rays entering the earth's atmosphere from outer space and also the internal exposure from radioactive elements through food, water and air. Natural radioactivity is wide spread in the earth's environment coming from Uranium (^^^U) and Thorium (^•'^Th) series and Potassiimi (^iQ, existing in various geological formations like soils, rocks, plants, water and air (EC, 1999; Singh et, al. 1999; Kumar et Al., 2003; Ahmed et al. 2006; Anjos et al.2005; Beretka and Mathew, 1985). Radiological implication of these radionuclides is due to the gamma ray exposure of the body and a- irradiation of lung tissues from inhalation of radon and its daughters. The assessment of gamma radiation dose and radon exhalation rate from nattiral sources is of particular interest as natural radiation is the largest contributor to external dose of the world population (UNSCEAR, 1993; El-Arabi, 2007). Radon, an- a radioactive inert gas is associated with the presence of radium and its ultimate precursor uranium. Naturally occurring heaviest radioactive toxic element uranium is found in traces in almost all types of rocks, soils, sands and water. As it can get dissolved in aqueous solutions in hexavalent (U*"^ form and can be precipitated as a discrete mineral in tetravalent (I/**) form. Uranium may form deposits in the earth's crust where the geological conditions become favorable. Although these radioactive elements occur in virtually all type of rocks and soils, their concentrations vary with specific sites and geological compositions. Short lived radon progenies have been established as causative agents of lung cancer (UNSCEAR, 1993; Lubin and Boice., 1997). 110 Under specific conditions such as those prevailing in the uranium mining environment lung dose due to radon progenies may be sufficiently high. Growing world wide interest in natural radiation has lead to extensive surveys in many countries. External gamma dose estimation due to terrestrial sources is essential not only due to its considerable contribution (0.46 mSv y'') to collective dose but also because of the variations of individual doses related to its path ways. These doses vary depending upon the concentrations of the natural radionuclides U and Th and their daughter products and ^°K, present in the soils and rocks which in turn depend upon the local geology and region in the world (Radhakrishna et, al 1993; Rudnic, Gao; 2003).To evaluate the radon risk in a given atmosphere it is necessary to identify and localize its sources. In the present study, a low level gamma ray spectrometric set up at the National Geophysical Research Institute, Hyderabad (India) and a coaxial n-type HPGe detector (EG&G, ORTEC, Oak Ridge, USA) at Inter-University Accelerator Centre, New Delhi (India) were used for the estimation of U, Th and K concentration (Cu, C-m and CK) in the coal, fly ash, rock, soil and sand samples. In few coal, fly ash and soil samples fission track registration technique using thermal neutrons in "APSRA" reactor at Bhabha Atomic Research Centre Mumbai India, was used for the estimation of U concentration. Also Radium concentration was measured using SSNTD's. Radiation doses and health risk have been estimated fi-om the activity concentration of natural radionuclides. Measurements were carried out on the following material samples having wide applications, collected fi-omdifferen t places and parts of the country: 1. Coal and fly ash samples, collected from different thermal power stations at Kolaghat, Durgapur, Bandel and Kasimpur situated in West Bengal and Uttar Pradesh states of India. Measurements have been made to estimate the enhancement of natural radioactivity in fly ash due to coal combustion. The thermal power plants all over the country produce a large quantity of fly ash which if not utilized or properly disposed off, will become one of the greatest menace to the nation and its inhabitants. 2. Rock and soil samples, collected fi"omdifferen t places of Jaduguda uranium mines in Singhbhum shear zone in the state of Jharkhand, India. Ill 3. Sand samples containing heavy minerals, collected from Chhatrapur and Erasama beach placer deposit, situated in a part of the eastern coast of Orissa, a newly discovered High Natural Background Radiation Area (HBRA) in India. 4.2 Energy savings and environmental benefits Coal is a technologically important material used for power generation. Its cinder (fly ash) is used in the manufacturing of bricks, sheets, cement, land filling etc. Coal and its by products often contain significant amounts of radionuclides, including uranium which is the ultimate source of the radioactive gas radon. Burning of coal and the subsequent atmospheric emission cause the redistribution of toxic radioactive trace elements in the environment. Most of the developing countries face energy scarcity and huge housing and other infrastructure shortage. Ideally in these countries materials for habitat and other construction activities should be energy efficient (having low energy demand). The following table shows some examples of energy savings achieved through the use of Fly Ash in the manufacture of conventional building materials. It should be noted that use of fly ash also improves the properties of building material, as shown in Table-1. (Building Materials in India: 50 Years - A Commemorative Volume, Building Materials & Technology Promotion Council, New Delhi, India, 1998) Table-1 Enei^ savings in the manufacture of building materials through the use of fly ash Building Material Composition Material Compared Energy savings (%) Portland pozzolana 75% Ordinary Portland 100% Ordinary 20 cement cement Portland Cement 25% Fly Ash Lime-pozzolana 25% Acetylene gas lime 25% Lime 75 mixture 75% Fly Ash 75% Calcined brick Calcium silicate 90% Fly Ash tailings Burnt Clay brick 40 brick 10% lime (waste source) Burnt brick 75% Clay Burnt Clay brick 15 25% Fly Ash 112 4.3 Natural radioactivity and radiation risk measurement in coal and fly ash samples Coal based thermal power plants contribute about 72% of the power generation in India. Indian coal is of bituminous type, having high ash content with 55-60 % ash and it has been estimated that -100 million tons of fly ash is produced per annum (Prasad et al. 1990; Vijayan and Behra. 1999; Baba, 2002 ). Coal like other materials found in nature, contains radionuclides like uranium, thorium and potassium. Combustion of coal enhances the natural radiation in the vicinity of the thermal power plant through the release of the radionuclides and their daughters in the surrounding ecosystem. Owing to its small size and hence large surface area the ash has a greater tendency to absorb trace elements that are transferred from coal to waste products during combustion (Gulec et al, 2001). In our previous measurements (Jojo et al., 1993a; 1993b) fly ash has been found to contain enhanced levels of uranium as compared to coal. Apart from inhalation, an additional radiation hazard can be the solids fall out, resulting in elevated concentration of natural radionuclides in the surface soils around the power plants (Bern et al., 2002). Due to considerable economic and environmental importance the collected fly ash has become a subject of world wide interest in recent years because of its diverse uses in manufacture of cement, clay ash bricks, ash bricks/blocks, cellular concrete blocks, asbestos products, in replacement of sand and cement in building materials, for filling of underground cavities, in construction of roads/ rail embankments/ reinforced earth walls, mine filling and in agriculture etc. Earlier studies (Mishra and Ramchandran., 1991) on coal and fly ash have shown that Indian coals contained 1.8- 6.0 ppm U and 6.0 -15.0 ppm of ^^^Th. But recent studies have indicated as high as 50 ppm ^^^Th and 10 ppm of U in the pond ash generated from coal combustion (Mandal and Sengupta, 2003). Radioactive properties of fly ash are of importance as some construction materials might raise the concentration of air borne radioactivity in indoor air to unacceptable levels, especially in places having low ventilation rates (Rawat et al., 1991 and Khan et al., 1992). In the present study, the activity concentrations of ^•'^U, •^^^Th, and """K radionuclides in the coal and fly ash samples collected from the different thermal power stations at Kolaghat, Durgapur, Bandel and Kasimpur situated in West Bengal and Uttar 113 Pradesh states of India have been measured to estimate their enhancement in fly ash due to coal combustion, are measured. Radiation doses and health risk have been estimated from the "^U, ^^^Th, and '^''K concentrations. 4.3.1 Geology of study areas The major thermal power plants of eastern India are Kolaghat, Durgapur and Bandel. They generate 1260, 350 and 530 MW of electricity respectively. The Kolaghat thermal powder plant is located in Midnapur district, West Bengal (22°27' to 22°25'N lat. and 87°50' to 87°55'E long.), on the western side of River Rupnarayan shown in figure-1. The thermal power plant consumes bituminous coal grade E and F. It has six units of 210 MW each and generates 1260 MW electricity. The Kolaghat region falls within the Kasai Delta of Contai formation of late Pleistocene age. The dominant lithotypes of the Contai formation are laterite, with mottled red and brown clays at the top. The major surface runoff in the region is the Denan-Dehati canal, which is the major outlet of the Rupnarayan River, and lies to the west of the thermal power plant. The Kasai River is the principal tributary of the Haldi River and enters the study areas from the north-west. The Denan-Dehati canal and a branch of the Kasai river are the major sources of portable water to about 100,000 people in the neighbouring 200 villages of the Kolaghat, Delta and Panskura blocks in West Bengal. The Durgapur thermal power station is situated in Burdwan district (22°56' to 23°53'N lat. and 86°48' to 88°25'E long.). West Bengal on the northern bank of river Damodar within 160 km WNW of Kolkata. At present, the power station has two working units and generates 350 MW of electricity. The Bandel thermal power plant is situated in the Hooghly district (23°39'32"to 23°01'20"N lat. and 87°30'15"to 88°30'20"E long.). West Bengal and is at 50 km from Kolkata. These three power plants use Gondwana coals of low sulphur and high ash content. Hence combustion of coal in these power plants results in generation of huge amounts of ash, which is disposed-off in large ponds located close to the thermal power plants. The ash, after being dumped, is kept exposed to the sun and in the course of time gets dried and becomes hard and compact. Ash ponds are situated close to domestic areas. Hence the radiation emitted 14 from them can affect the surrounding locality, on prolonged exposure. Kasimpur Thermal Power Plant (KTPP) is situated in the plains of the state of Uttar Pradesh and the wastes are discharged into the upper Ganges canal. Kasimpur Thermal Power Plant is one of the oldest thermal power plant in the country generates 533MW of electricity. 25 50 km -I Scale \< ( • # Kasimpm' theiinal power plant (TIP.) India * Kolaj^iat tliennal power plant (\V.B.) India F^ure -1. Location map of Kasimpur Thermal Power Plant (U.P.) and Kolaghat Thermal Power Plant (W.B.) India 115 4.3.2 Experimental A low level gamma ray spectrometric set up at National Geophysical Research Institute, Hyderabad, was used for estimation of the natural radionuclides, uranium (^^*U), thorium (^^^Th) and potassium (""^K) in coal and fly ash samples collected from the different thermal power stations at Kolaghat, Durgapur and Bandel situated in West Bengal of India. All collected samples were stored in polyethylene bags. They were dried for 24 h in an air-circulation oven at 110 °C. About 250 g of each sample was packed in plastic containers and sealed for four weeks (El-Arabi, 2005) for ^^^U and ^^^Th to attain secular 977 770 equilibrium with their decay products and to prevent Rn and Rn loss. The detector consisted of a 5" x6" Nal (Tl) crystal coupled to a 5" diameter photomultiplier tube. A 256- channel data set covering 0- 3 MeV is obtained through a Multi Channel Analyzer Tio 7*^7 (MCA) card (on a computer) that provided a gain-stabilized spectrum. ' U and Th were assessed from the intensity of the gamma ray peaks of their daughters: Bi (1.76 MeV) and Tl (2.62 MeV), assuming all daughter products to be in equilibrium whereas '* K was measured directly from its own gamma ray of 1.46 MeV. The samples were analyzed for a very long counting time (generally 7- 12 Ks). The standard samples with which the set-up needs to be calibrated are (1) containing thorium with a little uranium, (2) containing only uranium and (3) containing only potassium. In the present laboratory set up, the standard samples were prepared using powders obtained from the US Atomic Energy Commission, New Brunswick Laboratory. Assaying was carried out by the method followed at the National Geophysical Research Institute, Hyderabad. The details of the method of assaying are given elsewhere (Rao, 1974; Mandal and Sengupta, 2003; 2005). 4.3.3 Calculation of radiological effects 7^8 The activity concentrations of the natural radionuclides, uranium (""U), thorium ( Th) and potassium ('^^K) were measured in the coal, fly ash rock soil and sand samples and radiological parameters were calculated. The results are of great interest in the 0 t^^ ' 116 environmental radiological protection study, since all samples are widely used as building construction materials Radium equivalent activity (Raeq) Exposure to radiation is defined in terms of radium equivalent activity (Raeq) in Bq kg' to compare the specific activity of materials containing different amounts of U (^^Ra), "^Th and ^. It is calculated through the following expression (Yu et al., 1992; Hayambu et al., 1995): Raeq = Cu+1.43CTh + 0.07CK (1) Where Cu, Cn, and CR are the activity concentrations of ^^*U, ^^^Th and "^^K in Bq kg'* respectively. In the above equation for defining Ra^q activity it has been assumed that the same gamma dose rate is produced by 370 Bq kg"' of ^^*U or 259 Bq kg'' of ^^^Th or 4810 Bq kg'' of'^'K. There are variations in the radium equivalent activities of different materials and also within the same type of materials. The results may be important firom the point of view of selecting suitable materials for use in building construction materials. Absorbed gamma dose rate measurement (D) Outdoor air absorbed dose rate D in nGy h''due to terrestrial gamma rays at Im above the ground can be computed fi-om the specific activities, Cu, Cn, and CK of ^*U/^^^Ra, "^Th and ^'^ in Bq kg''- respectively by Monte Carlo method (UNSCEAR, 2000): D(nGyh'')= 0.462Cu + 0.604CTh+0.0417CK (2) To estimate the annual effective dose rate, E, the conversion coefficient from absorbed dose in air to effective dose (0.7 Sv Gy'') and outdoor occupancy factor (0.2) proposed by UNCSEAR (2000) were used. The effective dose rate in units of mSv y'" was calculated by the following relation: E (mSv y"') = Dose rate (nGy h"') x 8760 h xO.2 xO.7 Sv Gy'' x 10'* (3) External (Hex) and internal (Hin) hazard index The external hazard index is obtained from Raeq expression through the supposition that its allowed maximum value (equal to unity) corresponds to the upper 117 limit of Raeq (370 Bq kg"'). For limiting the radiation dose from building materials in Germany to 1.5 mGy y"' Krieger (1981) proposed the following relation for Hex: C C C ff !^ + ^ll]L + ±^ 118 Table-2. Activity concentration of radionuclides in coal(C-X) and fly ash (FA-X) samples from Kolaghat thermal power plant (West Bengal) Details of '»K(Bqkg-') '^U (Bq kg-') '''Th(Bqkg-') samples C-1 37 48 124 C-2 38 53 155 C-3 36 48 124 C-4 25 39 124 C-5 49 55 124 Average 37 49 130 Standard deviation 8 6 12 Rel. S.D.% 22 12 9 117 146 334 FA-1 FA-2 120 147 231 FA-3 115 144 234 FA-4 117 143 210 FA-5 99 142 308 110 • 147 226 FA-6 FA-7 118 136 308 FA-8 108 136 306 FA-9 114 126 298 FA-10 108 139 319 Average value 113 141 278 S.D. 6 6 44 Rel.Std.% 5 4 16 119 Table-3 Radium equivalent activity, gamma absorbed dose, outdoor external exposure, (external, internal) hazard index, in Coal (C-X) and Fly ash (FA-X) samples from Kolaghat thermal power plant (West Bengal) Gamma Radium Outdoor External Internal absorbed equivalent external hazard hazard Details of dose to air activity exposure index index samples rate (D) (Raeq) (mSv y') (Hi„) (nGyh-') (Hex) C-1 114 51 0.09 0.31 0.41 C-2 125 56 0.10 0.33 0.44 C-3 113 51 0.09 0.31 0.40 C-4 90 40 0.07 0.24 0.31 C-5 136 61 0.10 0.37 0.50 Average Value 116 52" 0.09 0.31 0.41 S.D. 16 7 0.01 0.04 0.06 Rel.S.D.% 13 13 11.8 13.6 14.6 FA-1 349 156 0.19 0.95 1.26 FA-2 346 153 0.19 0.93 1.26 FA-3 337 150 0.18 0.91 1.22 FA-4 336 145 0.18 0.91 1.22 FA-5 323 144 0.17 0.88 1.14 FA-6 336 149 0.18 0.91 1.20 FA-7 334 150 0.18 0.91 1.22 FA-8 324 145 0.17 0.88 1.17 FA-9 315 141 0.17 0.86 1.16 FA-10 329 147 0.18 0.90 1.18 Average Value 333 148 0.18 0.90 1.20 S.D. 10 4 0.01 0.02 0.03 Rel.S.D.% 3 3 5.5 3.20 2.73 120 01 200 I I I I I I •w T L_ Uranium s 110 iThorium •0 [Pottasium J!! 160 •Absorbed Dose Rate ^ 140 S Tl 1^ 1Z0 E 15 100 ^ 10 E 3 "5 GO ^ H £" 40 3 ^ 20 3 2 3 4 Number of Samples Figure-2. Bar diagram showdng activity concentration of ^^*U, ^^h, and '"'K and absorbed gamma dose rate in coal (Kolaghat) samples. 121 ? 2D0 £ s 150 s ^ f 100 3 50 81 d 0 12 3 4 S G 7 8 9 10 11 F^ure-3. Bar diagram showing activity concentration of ^^*U, ^^^h, and ''"K and absorbed gamma dose rate in Fly ash (Kolaghat) samples. 122 Radium equivalent activity in coal samples varies from 90 to 136 Bq kg' with an average value 116 Bq kg'', The absorbed gamma dose rates (D) in air at Im above the ground surface for the uniform distribution of radio nuclides (^^^Th, ^^^U and ''°K) are calculated on the basis of guidelines given by UNSCEAR, (2000).Gamma absorbed dose to air rate varies 40 to 61 nGyh'' with an average value 52 nGyh"' and the corresponding outdoor annual effective dose ranges from 0.07 to 0.10 mSv in coal samples. While in fly ash samples radiimi equivalent activity varies from 315 to 349 Bq kg''with an average value 333 Bq kg'', The absorbed gamma dose rates (D) varies from 141 to 156 nGyh'' with an average value 148 nGyh"' and the corresponding outdoor annual effective dose ranges from 0.17 to 0.19 mSv with an average value 0.18 mSv .The calculated values of Hex and H\„ for the coal and fly ash samples from Kolaghat thermal power plant studied in this work, range from 0.24 to 0.37 and 0.31 to 0. 50 respectively. While in fly ash samples range from 0.88 to 0.95 and 1.16 to 1.26 respectively. Since all these values for Hex are lower than unity, the fly ash is safe and can be used as a building construction material. 4.3.4.2 Durgapur thermal power plant The activity concentrations of ^^^U and ^''^Th and '"'K together with their average values in fly ash samples collected from Durgapur thermal power plant (West Bengal) India are given inTable-4. Activity concenfrations of ^^^U and ^^^Th varies from 84.8 ± 0.9 to 126.4 ± 1.3 Bq kg'' with an average value of 99.3 ± 1.3 Bq kg"' and from 98.1 ± 0.2 to 140.5 ± 0.3 Bq kg"' with a mean value of 112.9 ± 0.3 Bq kg'' respectively. The activity concentrations of ^^^Th are higher than those of ^^*U. 123 Table-4 Activity concentrations of "*U, "^Th and ""K in fly ash samples from Durgapur thermal power plant (West Bengal, India) Details of '^»U(Bqkg-*) *'K (Bq kg-1) Samples "'Th(Bqkg-l) IIT-Dl 95.8 ±1.1 109.1 ±0.2 300.7 ±2.1 IIT-D2 92.4 ±1.1 105.3 ±0.2 280.1 ±2.5 IIT-D3 95.7 ±1.1 109.3 ±0.2 290.4 ± 2.5 IIT-D4 93.4 ±1.8 101.0 ±0.3 267.1 ±2.5 IIT-D5 84.8 ± 0.9 107.6 ±0.2 272.4 ±2.1 IIT-D6 95.7 ±1.3 98.1 ±0.2 354.7 ±2.5 IIT-D7 114.9±1.3 136.9 ±0.3 344.5 ± 2.5 IIT-D8 94.9 ±1.0 103.8 ±0.2 287.8 ±2.1 IIT-D9 126.4 ±1.3 140.5 ± 0.3 364.9 ±2.5 IIT-Dl 0 98.8 ± 2.3 117.6 ±0.5 326.4 ± 2.5 No. of samples 10 10 10 Max. 126.4 ± 1.3 140.5 ± 0.3 364.9 ± 2.5 Min. 84.8 ±1.0 98.1 ±0.2 267.1 ±2.5 Average 99.3 ± 1.3 112.9 ±0.3 308.9 ±2.4 Standard deviation 11.5 ±0.4 13.8 ±0.1 34.0 ±0.2 124 In previous studies (Mandal and Sengupta, 2003) it has been observed that the activity concentrations of ^•'^Th is much higher than those of ^^*U in feed coal samples in Kolaghat thermal power station (W.B.) and combustion of coal enhances the radioactivity in fly ash (Jojo et al, 1993b). '^° K in ashes ranges from 267.1 ± 2.5 to 364.9 ± Bq kg"' with an average value of 308.9 ± 2.4-Bq kg''. Activity concentration of radionuclides are high as compared to those in fly ash fromth e thermal power station situated in other parts of India (Mandal and Sengupta, 2005; Kumar et al, 1999) e.g in Uttar Pradesh (Kumar et al., 1999) where the activity concentration of ^^^Ra (daughter product of ^^*U) is found to be 39.0 Bq kg'' and of "^Th 40.0 Bq kg'' but is comparable with those from Kolaghat thermal power station (Mandal and Sengupta, 2005) situated in the same state of West Bengal of India. It has been reported (Mandal and sengupta, 2005) that the concentration of radionuclide ^"'^U in the ash samples from KTPS are much higher than those in the ash samples of other thermal power stations in operation in different states of India. Ash samples from Durgapur thermal power plant as studied above contain a significant amount of radionuclides and also higher radon exhalation rates. To establish the correlation between ^^^U and ^•'^Th activity concentration and ^•'^Th and ''^K activity concentrations in the fly ash samples from Durgapur thermal power plant, the plots are shown in Figures. 4 and 5. A weak correlation exists between different quantities. Table-5 presents the radiation risk quantities obtained from U, Th and K activity concentrations. Figure- 6 shows a plot of the variation of ^^^U, ^^^Th, '*°K and absorbed dose rate in different samples fly ash samples fromDurgapu r thermal power plant. 125 "^"n-T I I I I I r I I I I I I I I I I I I I I I Linear fit ra 150 f! 8 i«> c o u R IN iiiiiiiit I I I 1 I I j-L 100 110 12D 130 140 150 Hi OonoertFdIon (Bq leg ) Figure-4. Variation of u activity concentration versus Th activity in (Durgapur) fly ash samples 126 600 V \ • K Concentration uine&i III r" 500 - S 4 » 4 D 1 "^ 400 o i 1 ^ " Iu 300 - c o . —T*^^*^^ • u .^ 200 t- 9 * i 4 100 * 90 100 110 120 130 140 150 232t. h Concentration |Bq kg^| Figure-5. Variation of ^^ activity concenti'ation versus "^h activity in (Durgapur) fly ash samples. 127 Table-5 Radium equivalent activity, absorbed gamma dose rate, effective dose rate and (external, internal) hazard index in fly ash samples from Durgapur thermal power plant (West Bengal, India) Radium Absorbed External Internal equivalent Effective dose gamma dose hazard hazard Details of activity rate (E) rate (D) index index samples (Raeq) (mSv y-') (nGy h-') (Hex) (Hi„) (Bq kg') IIT-Dl 272.9 122.7 0.15 0.74 1.00 IIT-D2 262.8 118.0 0.14 0.71 0.90 IIT-D3 272.3 116.3 0.14 0.74 0.99 IIT-D4 256.5 115.3 0.14 0.69 0.95 IIT-D5 257.7 115.5 0.14 0.70 0.93 IIT-D6 260.8 118.3 0.15 0.71 0.97 IIT-D7 334.8 150.1 0.18 0.91 1.22 IIT-D8 263.5 118.5 0.15 0.72 0.97 IIT-D9 352.8 158.5 0.19 0.96 1.30 IIT-DIO 289.8 130.3 0.16 0.79 1.05 Average 282.4 126.4 0.15 0.77 1.03 S.D. 32.3 14.7 0.02 0.09 0.12 Rel.S.D.% 11.4 11.6 13.3 11.6 11.7 128 2 4 6 10 Nunber of Samples F^ure-6 Bar diagram showing activity concentration of ^*U, ^^^h, and '*°K and absoibed gamma dose rate in different fly ash samples collected from Durgapur thermal power plant. 129 Radium equivalent activity in these samples varies from 265.5 to 352.8 Bq kg'' with an average value 282.4 Bq kg"', Absorbed gamma dose rate varies from 115.3 tol58.5 nGy h'' with a mean value of 126.4 nGy h'' which is ~3 times higher than the world average (43 nGy h"') as reported by UNSCEAR (1988). Thus the population within 80 km radius of the ash pond may be exposed to high dose rate. The corresponding outdoor annual effective doses range from 0.14 to0.19 mSv. The calculated values of Hex for the fly ash samples studied in this work, range from 0.69 to 0.96 and are very close to unity. Since all these values are lower than unity, the fly ash is safe and can be used as a construction material without posing significant radiological threat to population. But according to conservative estimate as calculated from eq.-6. Hex is close to unity. Thus according to Radiation Protection 112 (European Conmiissions, 1999) report care must be taken in using the fly ash as building material. Health risks are especially high in the area downward of the power plant. Being very minute, fly ash particles may tend to remain airborne for long periods leading to serious health problems as the airborne ash can enter the lungs through inhalation and may stick to lung tissues. Due to higher radon emanating power the lung tissues may be irradiated with a- particles from radon progeny to a high degree, increasing the possibility of lung cancer. These radionuclides in the fly ash may migrate from the waste disposal site to the underlying ground water body and may also accumulate in the top soil giving sufficient chances for the radionuclides to become enriched in soil. In recent years fly ash has been used as a replacement of sand and cement in pre mixed concrete, manufacture of blended fly ash Portland cement, aerated concrete, fly ash clay bricks and blocks and for filling for underground cavities etc. Thus it is quite important to estimate the radiation risk to the population from the radioactivity of flyash . 4.3.4.3 Bandel thermal power plant Radiometric analysis of fly ash samples from Bandel Thermal Power Plant (BTPP), Tribeni (West Bengal) are shown in Tables 6 & 7. Figure-7 shows a plot of the variation of U, Th, K and absorbed dose rate in different fly ash samples collected from Bandel thermal power plant (BTPP) West Bengal, India. Radium equivalent activity in these samples varies from 199.7 to 392.5 Bq kg"' with an average 130 value 312.8 Bq kg"', absorbed gamma dose rate varies from 92.3 to 173.0 nGy h'' with a mean value of 141.2 nGy h'' which is ~3 times higher than the world average (43 nGy h') as reported by UNSCEAR (1988). Thus the population within 80 km radius of the ash pond may be also exposed to high dose rate. The corresponding outdoor annual effective doses range from 0.11 to 0.21 mSv y'' with an average value of 0.17 mSv y"'. The calculated values of external hazard index Hex or internal hazard index Hm for the fly ash samples, range from 0.54 to 1.10 and from 0.71 to 1.38. Values of Hex are very close to unity. Since all these values are lower than imity, fly ash is safe and can be used as a construction material without posing significant radiological threat to population. 131 Table-6 nfi ^•^^ Aft Activity concentrations of U, Th and K in fly ash samples from Bandel thermal power plant (West Bengal) Details of samples "^U (Bq kg ' ) "'Th(Bqkg') ^"K (Bq kg') BTPP-1 139.0 115.6 396.8 BTPP-2 123.0 127.2 359.6 BTPP-3 110.7 132.0 403.0 BTPP-4 62.7 77.6 372.0 BTPP-5 118.1 181.6 210.8 BTPP-6 94.7 128.8 505.3 BTPP-7 92.1 117.2 480.5 No. of samples 7 7 7 Max. 139.0 181.6 505.3 Min. 62.7 77.6 210.8 Average 105.8 125.7 389.7 Standard deviation 23.1 . 28.4 88.7 Rel. S.D.: 21.8 23.0 22.8 Table-? Radium equivalent activity, absorbed gamma dose rate, effective dose rate, (external, internal) hazard index and effective dose equivalent in fly ash samples from Bandel thermal power plant (West Bengal) Radium Absorbed External Internal equivalent gamma dose Effective dose hazard hazard Details of activity rate (D) rate (mSv y') index index samples ( Raeq) nGy h' (Hex) (Hi„) Bqkg' BTPP-1 332.1 150.5 0.18 0.90 1.28 BTPP-2 330.1 148.6 0.18 0.90 1.23 BTPP-3 327.7 147.7 0.18 0.90 1.19 BTPP-4 199.7 • 92.3 0.11 0.54 0.71 BTPP-5 392.5 173.0 0.21 1.10 1.38 BTPP-6 314.3 142.6 0.17 0.86 1.11 BTPP-7 293.4 133.4 0.16 0.80 1.05 Max. 392.5 173.0 0.21 1.10 1.38 Min. 199.7 92.3 0.11 0.54 0.71 Average 312.8 41.2 0.17 0.86 1.14 Standard deviation 54.0 22.8 0.03 0.16 0.20 Rel. S.D.: 17.3 16.2 16.6 18.0 17.6 132 BOO •^^^^^•^^•g-^r— 'I • •••"• ••! •!•••••• I s lUEsiiim «B> JTioriiiri o 500 jpiot^iliin TS <» B a 400 £3 ice 300 £ 200 1 100 2 0 2 3 4 5 S 3 Nurnb^rdtsainpi&i Figure-7 Bar diagram showing activity concentration of ^*U, ^^h, and '*°K and absorbed gamma dose rate in different fly ash samples collected from Bandel thermal power plant. 133 4.4 Natural radioactivity in rock samples Rock samples were collected from different places far apart in the Jaduguda uranium mines in the shear zone. After collection, rock samples were crushed into fine powder by using Mortar and Pestle. Fine quality of the sample is obtained by using scientific sieve of 150 micron-mesh size. Before measurements samples were oven dried at 110°C for 24h and the samples were then packed and sealed in an impermeable airtight PVC container to prevent the escape of radiogenic gases radon (^^^Rn) and thoron (^^°Rn). About 300g sample of each material was used for measurements. Before measurements, the containers were kept sealed about 4 weeks in order to reach equilibrium of the U and Th and their respective progenies. After attainment of secular equilibrium between U and Th and their decay products, the samples were subjected to high resolution gamma spectroscopic analysis. In the present study Gamma ray spectrometric measurements were carried out at Inter-University Accelerator Centre, New Delhi using a coaxial n-type HPGe detector (EG&G, ORTEC, Oak Ridge, USA) was used for the estimation of U, Th and K concentration (Cu, Cih and CK) in the rock samples collected from different places of Jaduguda uranium mines in Singhbhum shear zone in the state of Jharkhand, India. Gamma dose was estimated fi-om the activity concentration of natural radionuclides U, ^^^Th and ''K. 4.4.1 Geology of the study area The Singhbhum shear zone is 200 Km. long arcuate belt in the state of Jharkhand State of India. Figure- 8 shows a geological map of the Singhbhum shear zone. Wide spread uranium mineralization is found to be associated with copper, nickel, molybdenum and other sulphides. The south-eastern part of the shear zone between Tampahar- Roam- Rakha and Surda- mosabani - Badia is rich in copper mineralization with major deposits, whereas the central part between Jaduguda-Bhatin-Nimidih, Narwapahr- Garadih-Turamidh and Mahuldih are rich in uranium (Sinha et al, 1990, Sengupta et al, 1996). Major uranium occurrences are found between Banguridih and Jaduguda and continue through the uranium and copper deposits of Surda-Roam, Rakha- 134 mosabani and Bagjata-Kanyakula-Dumardiha in the adjoining Mayurbhanj district of the state of Orissa, India. The shear zone was active over a long period of time from 2000 to 700 Ma and has been the loci for volcanism and for the emplacement of basic intrusives and potassium and soda-rich granites (Sengupta et al, 1996). Jaduguda mines located almost in the middle of the Singhbhum shear zone contain the richest U deposit in the entire belt and have been mined for its uranium ore for almost two decades. Two uraniferous ore bodies, 60m apart are delineated at Jaduguda and these are commonly referred to as fort wall lode or the central Jaduguda lode and the Hang-wall lode or the Eastern Jaduguda lode. The host rock for the mineralization is an apatite-magnetite-tourmaline- biotite- chlorite bearing quartz- rich schist. The grade of the ore increases from an average of 0.067% UBO? to about 0.20% UaOg. The mineralization of uranium has been found to exist up to a depth of 800m. It continues even deeper, though at the deeper levels it is affected by a major fault. The Narwapahr uranium deposit has a larger spatial extent with a total strike length being estimated to be more than 3 Km. (Bhola, 1971). 135 F'AKESTAN Si^gUkkuR Slwar Zone %9 N Sj TataNagarR.S, i ^""^ Tiimniclih d^ Jadusuda '^^-^ I •:';•.,- -1 CG(ngIasnBn.ta- "v '' ' ••' •'' Qourtite jDlanjcri F7^ Metabuks i "^J^P t^:> >c^:r;:::'c;^:?^ ^^ agj ata Figure- 8. Geological map of the Singhbhum shear zone, Jharkhand State with copper and uranium mineralization 136 4.4.2 Experimental Gamma ray spectrometric measurements were carried out at Inter-University Accelerator Centre, New Delhi using a coaxial n-type HPGe detector (EG&G, ORTEC, Oak Ridge, USA) for estimation of the natural radionuclides, uranium (^^^U), thorium ( Th) and potassium ( K) in rock and soil samples were collected from different places far apart in the Jaduguda uranium mines in the shear zone and some areas around the East Singhbhum shear zone and U-mining area of Jharkhand state, India. After collection, samples were crushed into fine powder by using Mortar and Pestle. Fine quality of the sample is obtained by using scientific sieve of 150 micron-mesh size. Before measurements samples were oven dried at 110°C for 24h and the samples were then packed and sealed in an impermeable airtight PVC container to prevent the escape of radiogenic gases radon (^^^Rn) and thoron (^°Rn). About 300g sample of each material was used for measurements. Before measurements, the containers were kept sealed about 4 weeks in order to reach equilibrium of the ^^*U and ^^^Th and their respective progenies. After attainment of secular equilibrium between U and Th and their decay products, the samples were subjected to high resolution gamma spectroscopic analysis. HPGe detector (EG&G, ORTEC, Oak Ridge, USA) having a resolution of 2.0 keV at 1332 keV and a relative efficiency of 20% was placed in 4" shield of lead bricks on all sides to reduce the background radiation from building materials and cosmic rays (Kimiar et, al; 2001). The detector was coupled to a PC based 4K multi channel analyzer and an ADC for data acquisition. The calibration of the low background counting system was done with a secondary standard which was calibrated with the primary standard (RGU-1) obtained from the International Atomic Energy Agency (IAEA). The efficiency for the system was determined using secondary standard source of uranium ore in the same geometry as available for the sample counting. For activity measurements the samples were counted for a period of 72000 seconds. The activity concentration of '*°K (CK) was measured directly by its own gamma ray of 1461 keV. As ^•'^U and ^^^Th are not directly gamma emitters, their activity concentrations (Cu and CTH) were measured through gamma rays of their decay products. Decay products taken for '^^^U were '^''^Pb: 295 and 352 keV and ^'^Bi: 609, 1120 and 1764 keV whereas for "^Th were ^^^Ac : 338, 463, 911 and 968 137 keV. 2'^Bi : 727 keV, ^'^Pb : 238 keV and "^Pa : 1001 keV gamma ray by assuming the decay series to be in equilibrium (Firestone and Shirely, 1998) Weighted averages of several decay products were used to estimate the activity concentrations of U and Th. The spectra were analyzed using the locally developed software "CANDLE (Collection and Analysis of Nuclear Data using Linux Net work)". The net count rate under the most prominent photo peaks of radium and thorium daughter peaks are calculated from respective count rate after subtracting the background counts of the spectrum obtained for the same counting time. Then the activity of the radionuclide is calculated from the background subtracted area of prominent gamma ray energies. Gamma ray spectrum of one typical rock sample is shown in Figure-9. The concentration of uranium, thorium and potassiimi is calculated using the following equation: E-xW xA Where S is the net counts/sec (cps) imder the photo peak of interest, a the standard deviation of S, E the counting efficiency (%), A the gamma abundance or branching intensity (%) of the radionuclide and W is the mass of the sample (Kg). 4.4.3 Results and discussion Uranium has a heterogeneous distribution in earth due to geochemical processes which have slowly recycled the crustal material to and fi-omth e earth's mantle. It is found with widely varying concentrations in different types of rocks. The uranium activity is widely distributed/dispersed in a heterogeneous media like the Singhbhum Shear Zone. The radioactivity (primarily uranium) can be observed in the entire zone. However significant mineralization is restricted to a few places and suitable locations in compatible host rocks. Earlier measurements undertaken by us supports this contention (Kumar et al., 2003; Sengupta et al., 1996). TabIe-9 presents the values of specific activities of U, Th and ''^K together with their corresponding total uncertainties. Figure-9, shows a typical gamma spectra of Jaduguda uranium mine samples JAD2, JAD5, JADl and JAD6. It shows a wide variation in the natural radionuclide concentrations as evident by the characteristic peaks. 138 Jadttguda samples JAD2, JAD5, JADl, JAD6 1 I t 1 ij ') I I I I I I j I 1 I I I 1 1 j I < 1 HI 4M3 tUS iMli iMU VMS JM&l mS2 Energj (fcfV) Figure -9. Spectra of the rock samples from Jaduguda uranium miiies: (1) JAD2, (2) JAD5 <3) JADl and (4) JAD6. The legends are: Ra-226 (V), Pb-214 (•), Bi-214<4) 139 Table-9. Average activity concentration of uranium, thorium and potassium of rocii samples from Jaduguda uranium mines in Singhbhum shear zone, Jharkhand, India, as well as the corresponding standard deviation. Sample Activity Concentration (Bq kg') ''\]. ^.^J^ 4Uj^ JADl 5970 ± 65 BDL BDL JAD2 40858 ±174 BDL BDL JAD3 9577 ± 95.06 BDL 9024 ±189 JA D 4 18297 ±136 BDL BDL JAD5 10863 ± 106 BDL BDL JAD6 20386 ±178 BDL BDL JAD7 123 ± 7 BDL 162 ±11 *BDL- Below Detection Limit. Table-10 Absorbed dose rate, annual effective dose, Raeq activity and (external, internal) hazard index in rock samples from Jaduguda uranium mines in Singhbhum shear zone, Jharkhand. 1 Radium External Internal Absorbed Annual No. equivalent hazard hazard dose rate effective dose Sample activity (Raeq) index index (nGyh-*) (mSvy-*) (Bqkg^) (Hex) (Hi„) JADl 2758.1 3.4 5970.0 16.1 32.3 JAD2 18876.4 23.2 40858.0 110.4 220.9 JAD3 4791.6 5.9 10208.7 27.7 53.6 JAD4 8453.2 10.4 18297.0 49.5 98.9 JAD5 5018.7 6.2 10863.0 29.4 58.7 JAD6 9418.3 11.6 20386.0 55.1 110.2 JAD7 63.6 0.7 134.3 0.4 0.70 Average value: - 7054.2 8.8 15245.3 41.2 82.2 S.D.:- 5655.6 6.8 12251.5 33.1 63.3 Rel. 80.2 77.2 80.4 80.3 80.6 Std. %:- 140 The results indicate reasonably high radioactivity from 123 ± 7 to 40858 ± 174 Bq kg'' for uranium with almost no Th which is expected in uraniferous regions. Only two samples showed potassium activity of 162 ± 11 Bq kg"' and 9024 ± 189 Bq kg''. The variation of natural radioactivity levels at different sampling sites are due to the variation of concentrations of these elements in geological formations. From the values of Cu, CTH and CR it is possible to evaluate the annual effective dose due to y-rays at Im above the ground. Annual effective dose rates are estimated using simple calculations consi^iering indoor occupancy factor of 0.8, proposed by UNSCEAR report (1993, 2000) which implies that 20% of the day is spent out doors, on an average around the world. Table-10 summarizes the values of absorbed dose, annual effective dose, radium equivalent activity and external and internal hazard index. Absorbed dose rates vary from 63.6 to 18876.4 nGy h"' with an average value 7054.2 nGy h"'. The annual external effective dose rates vary from 0.7 to 23.2 mSv y'', with an average value of 8.8. mSv y''. Radium equivalent activity (Raeq) ranges from 134.3 to 40858.0 Bq kg"' with an average value of 15245.3 Bq kg'' and the calculated values of external index hazard (Hex) vary from 0.4 to 110.4 with an average value of 41.2. The internal exposure to ^^^Rn and its radioactive progeny is controlled by the internal hazard index H,n. Computed values of H,n vary from 0.70 to 220.9 with an average value of 82.2. In Table-11, a comparison of radiometric and radiological data has been presented with those computed from the radiometric data obtained from our earlier measurements (Singh et al., 1999, Kumar et al., 2003, Sengupta and Prasad, 2001) carried out on the geological samples from different mineralization zones in Singhbhum shear Zone. 141 Table-11 Radium equivalent activity, absorbed dose rate, external hazard index and effective dose rate in rock samples from different mine regions in Singhbhum shear zone Places Radium equivalent Absorbed Internal External EfTective dose Activity dose rate hazard Hazard rate ( Bq kg-*) (nGy h') index index (mSv y-') (Hin) (Hex) Mosbani mines 524.7 233.0 1.7 1.4 0.28 (Cu-U mines) Pathargora 919.7 428.8 4.7 2.4 0.52 mines (Cu mines) Bhatin mines 5313.1 3155.4 29.3 14.9 3.86 (Cu-U mines) Badia 522.9 262.6 2.0 1.5 0.32 (Cu-U mine) Rakha mines 892.8 415.7 4.6 2.4 0.50 (Cu-U mines) Surda mines 1905.2 880.7 10.1 5.2 1.08 ( Cu mines) Jaduguda 15245.3 7054.2 82.9 41.2 8.80 (U-mines Present study) The concentration of uranium in the different rock samples from the copper and uranium mines in the shear zone exhibits uneven distribution of uranium. A significant non uniformity is exhibited by the samples from Jaduguda. The average uranium concentration and radon exhalation rate are highest in Jaduguda U mines. At Rakha and Pathargora both Cu and U mineralization occur while Bhatin is enriched in uranium with the absence of Cu. Jaduguda region has high grade uranium ores. Absorbed dose rate varies from 233.0 to7054.2 nGy h''. Jaduguda U-mine samples having the highest value. Bhatin Cu-mines give also higher values as these are nearer to Jaduguda U-mines. At Surda U and Cu mineralization are closely associated though not always coincident. The calculated values of Hex for the rock samples range from 1.4 to 41.2 and values of Hin in these samples varies from 0.28 to 8.80. As all these values are higher than unity, the region is not safe and may pose significant radiological threat to the population. 142 4.5 Natural radioactivity in soil samples 4.5.1 Experimental The natural radioactivity in soil comes from "*U, ^^^Th and from natural ""K. Some other terrestrial radionuclides, including those of the ^'U series, and "^Lu exist in nature but at such low levels that their contributions to the dose in the humans are small. Artificial radionuclides can also be present such as '^'Cs, resulting from fellout from weapons testing. The radiological implication of these radionuclides is due to the gamma ray exposure of the body and irradiation of lung tissue from inhalation of radon and its daughters. Therefore, the assessment of gamma radiation dose from natural sources is of particular importance as natural radiation is the largest contributor to the extemal dose of the world population (UNSCEAR, 1988). In the present study natural radio nuclides (^*U, ^^h and ''^'K) concentration from the soil samples from Rajmahal region and some areas around of the East Singhbhum shear zone U-mining area of Jharkhand state of India also using high resolution y -ray spectroscopic system are measured for the estimation of effective radiation dose to assess the radiation risk to the inhabitants. Gamma spectrometric measurements were carried out at Inter-University Accelerator Centre, New Delhi using a coaxial n-type HPGe detector (EG&G, ORTEC, Oak Ridge, USA). The detector has a resolution of 2.0 keV at 1332 keV and relative eflficiency of 20% and was placed in 4" shield of lead bricks on all slides to reduce the background radiation from building materials and cosmic rays. As the soil is the basic ingredient used in construction materials in India, estimation of the radiation risk to the population is quite important and can be computed from the activities of the radio-nuclides present in the sample. 4.5.2 Results and discussion A typical gamma ray spectra of soil samples is shown in Figure-10. Natural radionuclides (^*U, ^^Th and '"'K) activity concentration from the soil samples collected from Rajmahal region of the East Singhbhum shear zone of Jharkhand state of India are given in Table 12. Radium equivalent, absorbed gamma dose rate, annual effective dose rate, extemal hazard index and intemal hazard index for the soil samples are given in Table 13. 143 Spectra of soihiimples Markors ID lil.V {i)si3.n (3) 1«2.14 Id i(t ^ Id Id id Id •1.1 328.8 ()58.7 988.6 1318.5 16414 1978.2 2308.1 Energy (keV) Figure-10. Spectra of the soil samples from East Singhbhum shear zone U-mining area of Jharichand state of India. The legends are: Ra-226 (V), Pb-214 (•), Bi-214(4) 144 TabIe-12 Natural radioactivity in soil samples collected from Rajmahal region of Jharkhand, State India Name of Samples U (Bq kg-') Th (Bq kg') K(Bqkg') Deoghar 826.6 ±14.0 DDL 3691.0 ±5 9.1 Crodda 1079.8 ±15.8 118.1 ±5 .2 1804.12 ±18.0 Madhupur 2115.0 ±65.7 4414.0 ±74.7 BDL Shahibganj 1629.6 ±22.8 303.1 ±39.7 4413.0 ±71.8 Jamtara 1156.7 ±16.6 50.1 ±1.5 1626.4 ±36.0 Pakiir 866.08 ±18.99 BDL 3471.0 ±20.0 Barawaha 755.2 ±11.9 BDL 1354.0±31.1 Average value 1204.1 ±23.7 1221.3 ±30.3 2726.6 ± 39.3 S.D. 460.9 ±17.5 1845.6±29.7 1174.3 ± 19.8 Rel. Std. % 38.27 151.12 43.07 *BDL- Below detection limit Table-13 Radium equivalent activity, absorbed gamma dose rate, effective dose rate, and external hazard index in soil samples collected from Rajmahal region of Jharkhand, State India Details of Radium Absorbed Effective External Internal samples equivalent gamma dose dose rate hazard hazard activity rate (D) (mSvy') Index index (Raeq) (Hex) (Hin) Deoghar 1085.0 535.8 0.66 2.99 5.24 Crodda 1375.0 645.4 0.79 3.74 6.67 Madhupur 8427.1 3643.2 4.46 22.75 28.48 Shahibganj 2372,0 1120.0 1.36 6.48 10.90 Jamtara 1342.1 632.4 0.77 3.64 6.78 Pakur 1109.1 544.9 0.66 3.06 5.40 Barawaha 850.0 405.4 0.49 2.32 4.36 Average 2365.7 1075.3 1.31 6.32 9.69 value S.D. 2515.3 1068.9 1.30 8.83 7.91 Rel. Std. % 106.3 99.4 99.23 105.45 81.6 145 Activity concentrations were found to vary from 755.2 ± 11.9 to 2115.0 ± 65.7 Bq kg'' with an average value of 1204.4 ± 23.8 Bq kg"' for ^^^U, from 50.1 ±1.5 to 4414.0 ± 74.7 Bq kg"' with an average value of 1221.3 ± 30.3 Bq kg"' for "^Th and 1354.0 ±31.1 to 4413.0 ± 71.8 Bq kg'' with an average value of 2726.6 ± 39.3 Bq kg"' for ^V in the soil samples collected from Rajmahal region, Jharkhand. The values of absorbed gamma dose rate, annual effective dose rate, radium equivalent activity (Raeq), external hazard index Hex, and internal hazard index Hjn in the soil samples collected from Rajmahal region are presented in Table 13. Absorbed gamma dose rate varies from 405.4 to 3643.2 nGyh'' with a mean value of 1075.3 nGyh''. Effective gamma dose rate varies from 0.49 to 4.46 mSv y"' with an average value of 1.31 mSv y''. Radium equivalent activity varies from 850.0 to 8427.1 with a mean value of 2365.7 Bq kg"'. Values of Hex calculated for the soil samples studied in this work range from 2.32 to 22.8. Since most of these values of Hex are higher than unity, the use of soil from this region as construction material may give significant radiation dose and pose radiological threat to the population. 4.6 Natural radioactivity in sand samples The Chhatrapur beach placer deposit and Erasama beach placer deposit are known as High Back Ground Radiation Area (HBRA) due to the presence of radiogenic heavy minerals. This is characterized by a number of well developed sand dunes, which are parallel to the coast. Heavy mineral concentrations are found as discrete patches within the beach sands, consisting dominantly of quartz sands. Distribution of naturally occurring radionuclides mainly "*U, ^•'^Th and ''^K depends on the distribution of rocks from which they originate and on the processes through which they are concentrated. Higher concentrations of radionuclides such as ^^^U. ^•'^Th and ''"K occur in minerals such as monazites and zircons. Around the world though, there are some areas with sizable populations that have high background radiation levels. The highest are found primarily in Brazil, India and China. The higher radiation levels are due to high concentrations of radioactive minerals in sand and soil.The Chhatrapur beach placer deposit is located in Ganjam District. Orissa on the southeastern coast of India. Erasama beach is also the part 146 of the eastern coast of Orissa state, India. The area extended over a coastal length of 24 km and average width more than 1 km, trending almost NE-SE, bounded by the Bay of Bengal in the south east and coastal alluviums of Pleistocene age in the north west side. This area is almost like a flat terrain with a gentle slope towards the Bay of Bengal and characterized by recent slope alluvium and costal deltaic plain sediments. As sand is frequently used as a building construction material in India, the estimation of radiation risk to the population is quite important and can be computed from the activity concentration of the radio-nuclides present in the sand samples. 4.6.1 Result and discussion To estimate the gamma dose rate activity concentrations of U/ Ra, Th and 40K for these samples were taken from (Mohanty et al. 2004a) and shown in Table-14. Table-15 suirmiarizes the values of absorbed dose, armual effective dose, radium equivalent activity, external and intemal hazard index in sand samples collected from Chhatrapur beach placer deposit. 147 TabIe-14 Activity concentrations of ^"'^U, ^^h and '***K in sand samples collected from Chhatrapur Beach (Orrisa) S.No Sample Name ""UCBqKg-') "^Th (Bq Kg^) ^"K(Bq Kg') 1 CHSl 120 ±30 1100 ±40 75 ±20 2 CHS2 200 ± 30 2300 ± 50 135 ±20 3 CHS3 250 ± 25 2600 ± 50 100 ±25 4 CHS4 250 ± 25 2650 ±50 120 ± 50 5 CHS5 350 ±25 4300 ± 40 120±10 6 CHS6 • 270 ± 25 3200 ± 50 100 ±30 7 CHS7 120 ±30 1100 ±50 225 ±20 8 CHS8 60 ±25 800 ± 50 200 ± 30 9 CHS9 170 ±25 1600 ±50 100 ±30 10 CHS 10 80 ±30 650 ± 60 250 ± 60 11 CHS 11 150 ±25 1600 ±50 60 ±35 12 CHS 12 150 ±30 1600 ±50 100 ±50 13 CHS 13 300 ±30 3400 ± 50 70 ±60 14 CHS 14 60 ±30 550 ±50 250 ± 40 15 CHS 15 150 ±25 1200 ±50 150 ±20 16 CHS 16 120 ±25 700 ± 50 350 ±30 17 CHS 17 200 ± 30 2400 ± 40 50 ±30 18 CHS 18 300 ±30 3600 ± 50 50 ±30 19 CHS 19 600 ± 25 7600 ± 60 50 ±30 20 CHS20 500 ±30 6000 ± 50 50 ±30 Minimum value 60 ±25 550 ±50 50 ±30 Maximum Value 600 ±25 7600 ±60 350 ±30 Average: 220 ±28 2448 ±50 130 ±33 S.D.: 137 ±3 1809 ±5 81 ± 13 Rel. S.D.: 62 ±9 74 ±10 .63 ±40 148 Table 15. Effective dose equivalent, radium equivalent activity, annual effective gamma dose rate and external Hazard index of sand samples Chhatrapur Beach (Orrisa) S.No. Radium Absorbed dose Annual External Internal equivalent rate (nGy h'') effective hazard iazard (Bqkg-') gamma index index dose rate Hex Hin (mSv y-') CHSl 1698.3 723.0 0.89 4.9 4.9 CHS2 3498.5 1487.2 1.82 9.5 10.0 CHS3 3975.0 1690.1 2.07 10.7 11.4 CHS4 4047.9 1721.1 2.11 10.9 11.6 CHS5 6507.4 2763.9 3.39 17.6 18.5 CHS6 4853.0 2061.7 2.53 13.1 13.8 CHS7 1708.8 729.2 0.89 4.6 4.9 CHS8 1218.0 519.3 0.64 3.3 3.5 CHS9 2465.0 1049.1 1.29 6.7 7.1 CHS 10 1027.0 439.9 0.54 2.8 3.0 CHS 11 2442.2 1661.9 2.04 6.6 7.0 CHS 12 2445.0 1039.9 1.28 6.6 7.0 CHS 13 5166.9 2195.1 2.69 14.0 14.8 CHS 14 864.0 370.4 0.45 2.3 2.5 CHS 15 1876.5 800.4 0.98 5.1 5.5 CHS 16 1145.5 492.8 0.60 3.1 3.4 CHS 17 3635.5 1544.1 1.89 9.8 10.4 CHS 18 5451.5 2315.1 2.84 14.7 15.5 CHS 19 11471.5 4869.7 5.97 31.0 32.6 CHS20 9083.5 3857.1 4.73 24.5 25.9 Minimum 864.0 370.4 0.45 2.3 2.5 Maximum 11471.5 4869.7 5.97 31.0 32.6 Average 3729.0 1616.6 1.98 10.1 10.7 S.D 2719.3 1446.5 1.4 0 7.3 7.7 Rel. Std. % 72.9 70.9 70.7 72.3 72.0 149 From the activity concentration of ^''^U, ^^^Th and ''^K in these sand samples the radium equivalent due to the presence of radionuclides is calculated and is found to vary from 864.0 to 11471.5 Bq kg"' with an average value of 3729.0 Bq kg''. Absorbed gamma dose rate in air due to the naturally occurring radionuclides ( U, Th and K) varies from 370.4 to 4869.7 nGy h'' with an average value of 1616.6 nGy h'' which is much higher than the world average value of 55 nGy h"' (UNSCEAR,1988), while effective gamma dose rate varies from 0.45 to 5.97 mSv y"' with an average value of 1.40 mSv y"'.Values of external hazard index, Hex for the sand samples studied in this work range from 2.3 to 31.0 with a mean value of 10.1. Computed values of H,n vary from 2.5 to 32.6 with an average value of 10.7. Situated in a part of the eastern coast of the state of Orissa, India, newly discovered Erasama beach placer deposit is also high natural background radiation region (HBRA) which is due to the presence of radiogenic heavy minerals. The sand samples containing heavy minerals, were collected from Erasama beach placer deposit by the grab sampling method at interval of ~ 1 Km. Activity concentrations of ^^*U, '^•'^Th and "* K in Bq kg"'' respectively and have been taken from the earlier study (Mohanty et al., 2004b) and shown in Table-16. Values of absorbed dose, annual effective dose, radium equivalent activity, external and internal hazard index in sand samples is shown in Table 17 Radium equivalent varies from 1451.0 to 7229.4 Bq kg"' with an average value of 4410.9 Bq kg"'. Absorbed gamma dose rate in air due to the naturally occurring radionuclides (^^*U, ^^^Th and *°K) varies from 621.2 to 3074.8 nGy h"' with an average value of 1879.5 nGy h'' which is also much higher than the world average value of 55 nGy h"' (UNSCEAR,1988), while effective gamma dose rate varies from 0.8 to 3.8 mSv y"' with an average value of 2.3 mSv y''.Values of external hazard index. Hex for the sand samples studied in sand samples range from 3.5 to 20.8 with a mean value of 12.8. As all the values of Hex and H,n are higher than unity, the use of sand from Chhatrapur beach and Erasama beach region as building construction material may give significant radiation dose and pose radiological threat to the population. 150 Table-16 Activity concentrations of ^*U, ^^Th and '"'K in sand samples collected from Erasama Beach (Orrisa) S.No Sample Name ""U (Bq Kg-) "^Th (Bq Kg') ^"K (Bq Kg-') 1 ERl 200 ±15 1600 ±50 200 ± 30 2 ER2 400 ± 20 2600 ± 60 150 ±20 3 ER3 • 250 ±10 2000 ± 50 180 ±25 4 ER4 450 ± 20 3000 ± 70 200 ± 25 5 ER5 450 ± 20 2900 ± 50 120 ±25 6 ER6 150±10 900 ± 30 200 ± 30 7 ER7 200 ±15 1100 ±30 200 ± 25 8 ER8 500 ± 25 4500 ± 80 100 ±15 9 ER9 400 ± 20 2900 ± 40 250 ±30 10 ERIO 500 ± 25 3500 ±50 180 ±25 11 ERll 300 ±15 1750 ±40 250 ±30 12 ERl 2 500 ± 30 4600 ± 70 150 ±20 13 ERl 3 500 ± 30 4700 ± 80 120 ±20 14 ERl 4 300 ± 20 2050 ± 40 230 ±15 15 ERl 5 250 ±15 1800 ±30 300 ± 20 16 ERl 6 200 ±10 1900 ±40 250 ± 40 17 ERl 7 350 ± 20 3400 ±40 180 ±30 18 ERl 8 450 ± 25 4000 ± 70 170 ±20 19 ERl 9 250 ±15 2400 ± 40 ^ 200 ±20 20 ER20 400 ± 20 3100 ±50 200 ± 25 21 ER21 250 ± 20 2300 ± 40 180 ±20 22 ER22 400 ± 25 3600 ± 50 120±15 23 ER23 500 ±30 3900 ± 50 100 ±20 24 ER24 450 ± 20 3300 ± 40 150 ± 25 Minimum value 150 ±20 900 ±30 100 ±15 Maximum Value 500 ±25 4700 ±80 300 ±20 Average: 358 ± 20 2825 ±50 183 ± 24 S.D. 114 ±6 1056 ±15 50 ±6 Rel. S.D.% 32 ±30 37 ±30 27 ±25 151 Table 17. Effective dose equivalent, radium equivalent activity, annual effective gamma dose rate and external Hazard index of sand samples collected from Erasama beach placer deposit, Orissa Annual Internal Radium Absorbed effective External Sample hazard equivalent (Bq dose rate ( gamma hazard index code. index kg') nGyh-i) dose rate (Hex) (Hi„) (mSvy-^) ERl 2502.0 1067.1 1.3 6.8 7.3 ER2 4128.5 1761.5 2.2 11.2 11.4 ER3 3122.6 1331.0 1.6 8.4 9.1 ER4 4754.0 2028.2 2.5 12.8 14.1 ER5 4605.4 1964.5 2.4 12.4 13.6 ER6 1451.0 621.2 0.8 3.9 3.5 ER7 1787.0 765.1 1.0 4.3 5.4 ER8 6942.0 2953.2 3.7 18.9 20.1 ER9 4564.5 1946.8 2.4 12.3 13.4 ERIO 5517.6 2352.5 3.0 14.9 16.2 ERll 2823.0 1206.0 1.5 7.6 8.4 ERl 2 7088.5 3015.7 3.8 19.1 20.5 ERl 3 7229.4 3074.8 3.9 19.5 20.8 ER14 3247.6 1386.4 1.7 8.8 9.6 ER15 2845.0 1215.2 1.5 7.7 8.4 ERl 6 2934.5 1250.4 1.6 7.9 8.5 ERl 7 5224.6 2222.8 2.8 14.1 15.1 ERl 8 6181.9 2630.9 3.3 16.7 17.1 ERl 9 3696.0 1573.4 2.0 10.0 10.6 ER20 4847.0 2065.5 2.6 13.1 14.2 ER21 3551.6 1512.2 1.9 9.9 10.3 ER22 5556.4 2363.8 3.0 15.0 16.1 ER23 6084.0 2590.8 3.3 16.4 17.7 ER24 5179.5 2207.4 2.8 14.0 15.2 Minimum 1451.0 621.2 0.8 3.9 3.5 Maximun1 7229.4 3074.8 3.9 19.5 20.8 Average 4410.9 1879.5 2.3 11.9 12.8 S.D 1612.5 684.9 0.8 4.3 4.7 R. Std. % 36.6 36.6 36.5 36.1 36.7 152 4.7 Uranium concentration in building construction materials using Fission Track Registration technique. Ever since the genesis, biosphere has been exposed to natural environment radiation originating from the atomic species Uke uranium, thorium, potassium, and traces of very long-lived naturally occurring nuclides. The technological endeavours of human beings have modified the levels of radiation exposure slightly. The radiation dose received by human beings from indoor radon and its progeny is the largest of all dose received either from natural or man-made sources UNSCEAR, (1988). The Southwest coast of the Kerala State in India is known to have very high levels of natural background radiation owing to the rare earths rich monazite sand available in large amount. Sand present in the region is an orthophosphate of thorium and rare earths and typically contains about 9% thorium oxide and 0.35% uranium oxide (Chougaonkar, et al., 2004). Sand and soil are commonly used in the building construction materials. There exists a unique situation where a large population is being exposed to a high level of radiation all through their life-span. Thus it was thought proper to estimate U concentration in building materials used in that region. Sixty samples belonging to twelve categories of building materials commonly used in the region are taken for the investigation for the analysis of uranium concentration using the fission track registration technique (Singh et al, 1998). This is a well-acclaimed method for micro-mapping uranium even at sub ppb levels. Uranium concentrations were determined using the 'dry method'. 4.7.1 Experimental For the uranium analyses in some soil, fly ash and some building material samples fission track registration technique was used. The method is highly reliable, sensitive and simple. At the same time it has the potential capability of micro mapping even for sub ppb levels of fissionable impurity. The fissionfragment s resulting from (n, f) reaction on ^^^U were observed by track etch detectors kept in contact with the sample or standard material . By chemical etching tracks were formed. From the number of tracks in the detector, the uranium concentrations in the samples were determined. (Singh et al., 1998). 153 All samples were grinded properly and sieved through 100 mesh. A homogenous mixture of accurately weighed sample powder and methyl cellulose in the ratio 1:2 ratio by weight was made. 200 mg of this mixture a thin pellet of about 1mm thick and 1.3 cm in diameter was prepared by a hydraulic pellet machine applying a pressure of about 5 Xl cm . Pellets of standard glass of known uranium concentration ( Azam and Prasad, 1989) were also prepared in the similar manner. Each of these pellets was sandwiched between a pair of Makrofol -KG plastic track detector pieces of same size. All the pellets of sample and standard glass were enclosed in an aluminum capsule and sealed tightly to make the intimate contact. This assembly was irradiated with a thermal neutron fluence of about lO'^ cm'^ (nvt) at APSARA reactor, Bhabha Atomic Resaerch Centre Mumbai, India. After irradiation the detector pieces were separated from the pellets, and etched in 6.25 N KOH solution at 60° for 20 minutes in a constant temperature water bath to reveal the fissiontracks . The tracks produced in the detector by the fission of ^^^U were scanned with an optical microscope at a magnification of 400 x. The uranium concentration was calculated using the expression f J Y U,=U. • X Is (8) T V^ A Where the subscripts x and s stand for the sample and standard, respectively, T is the fission track density and I is the isotopic abundance ratio of ^^^U and ^^U. The ratio Is/Ix has been taken to be unity assuming that the isotopic abundance ratio is the same for the sample and standard substances. 4.7.2 Results and discussion Results of uranium analysis of the building materials are presented in the TablelS. Levels of uranium as well as its specific activity in the building materials are determined. Uranium levels are found to vary from 1.04 ± 0.8 [ig g'' to 6.95 ± 2.1|ig g"' corresponding to the specific activity from 25.8 ±9 Bq kg'' to 172.4 ±28 Bqkg"' respectively. A very recent study held in Egypt shows that ^^^Ra concentration is maximum having a mean value of 205 ± 83 Bq kg"'(Ahmed, 2005).in marble among the 154 building materials. But in the present study the emanation rate from marble is found to be low. This contradiction may be either due to low emanation power fraction of marble or due to low level of ^^*Ra in the samples. This aspect needs to be addressed. Fission track registration technique was also used for the measurement of uranium concentration in some coal, fly ash and soil samples collected from the following places: (a) Fly ash from the thermal power plants at Kasimpur (Aligarh), Parichha(Jhansi) and Obra (Mirzapur) situated in the state of Uttar Pradesh. (b) Soil from different places of Mathura, Agra and Kasimptir & Obra thermal power plants in the state of Uttar Pradesh and some places of the State of Rajasthan. Results of uranium analysis in these samples are presented in the Table 19 Comparison of the relative uranium concentration shows that uranium concentration in fly ash samples is higher than that in coal and soil samples collected from different power plant and places in India.. 155 Table -18 Concentration of uranium and radon emanation in different building materials Rn emanation U-activity U-concentration rate ±SD S.N. Building material ±SD(Bqkg') ± SD (figg') (mBqm"^ h') 1. Brick: Top layer of the 2.24 ± 0.9 55.6 ±12 227 ± 33 furnace 2. Brick: Middle layer of 2.04 ± 0.8 50.6±12 231 ±29 the furnace 3. Brick: Bottom layer of • 1.95 ±0.8 48.4 ±11 257 ±36 the furnace 4. Cement hollow brick 1.45 ±0.8 36.0 ±10 44 ± 12 5. Cement Solid brick 2.45 ±1.1 60.8 ±16 141 ±18 6. Plastered brick 6.95 ±2.1 172.4 ±28 308 ±58 7. Concrete 1.84 ±0.8 45.6 ±11 181±21 8. Mosaic 1.04 ±0.8 25.8 ±9 136±21 9. Kadappa 1.08±1.1 26.5 ± 6 30 ±9 10. Ceramic tile 1.05 ±0.9 26.0 ± 5 17±7 11. Granite 1.25 ±0.9 28.0 ±9 25 ±9 12. Marble 1.81 ±1.2 45.0 ±10 86 ±18 156 Table-19 Uranium concentration in soil, fly ash and coal samples Detail of samples Uranium Concentration (ppm) (a) Soil 1. Kasimpui-(U.P.) 1.9 2. Mathura (U.P.) 1.6 3. Agra (U.P.) l.I 4. Obra Mirzapur (U.P.) 2.9 5. Hanuman Garh (Rajasthan) 1.3 6. Banswara (Rajasthan) 1.0 7. Mohan Garh (Rajasthan) 0.9 8. Sabai Madhopur (Rajasthan) 1.7 (b) Fly ash 1. Kasimpur - Unit A (U.P.) (i) 21.4 (ii) 28.4 2. Kasimpur - Unit B (U.P.) (i) 21.7 (ii) 26.7 3. Parichha, Jhansi (U.P.) (i) 24.9 (ii) 27.0 4. Obra Mirzapur(U.P.) (i) 23.4 (ii) 24.3 (c) Coal (Average Value) 14.3 157 4.8 Measurement of effective radium content in sand samples Radium is one of the radionuclide of concern. This mainly enters the body through food and tends to follow calcium in metabolic processes to become concentrated in bones. The radiation given off by radium bombards the bone marrow and destroys tissues that produces red blood cells. It also can cause bone cancer. Radium is chemically similar to calcium and is absorbed from soil by plants and passed up the food chain to humans. The radium content of a sample also contributes to the level of environmental radon as radon is produced from ^^^Ra through alpha decay. By estimating the radium content of a sample we can predict if it can be used as a construction material. In the present study track etch technique using LR-115 plastic track detectors has been used to measure the effective radium content of sand samples collected from Chhatrapur beach of Orissa State (India) and also of some samples collected from rivers. 4.8.1 Experimental The sand samples were collected from the Chhatrapur beach placer deposit by the grab sampling method. The study area is extended over a length of 20 Km trending NE-SW with an average width of more than 1.5 Km. The experimental arrangement is shown in Figure-ll: Dried sample (lOOg) was placed at the bottom of the plastic Can. The mouth of the Can was sealed with a cover fixed with LR-115 type II plastic track detector in such a way that the sensitive surface of the detector faced the sample. 158 Iiieakd Cover LR-115Type I nPIasiicTrick Detector Surface 7 cm h Plastic Can 10 cm RADON GAS i L. i i Sand I •• •• t. fT ••H t^ uf^ 1^^ •• t L r T' *JLJ*" Sample t- < •• •• (lb < ••k •• •• • •• t\ji •• •• •! *IJ * ^ut •• L_4i Figure-ll Experimental Setup for measurement of radium content in sand samples. 159 4.8.2 Theoretical details The detector records the tracks of alpha particles emitted by radon gas produced through the alpha decay of radium. The track density p (in track m'^) is related to the radon activity concentration CRH (in Bqm'^) and the exposure time T by the formula ( Somogyi et al, 1986b): P = KC,„r (1) where K is the sensitivity factor of LR-115 track detector. The value of K for a Can of radius 3.5 cm and height 10 cm is 1/30 tracks cm'^ d"' (Bqm"^)'' with an uncertainty of 15% (Somogyi, 1986a). It is necessary that for this value of K, the etching is carried out to reduce the thickness of the LR-115 type detector to about 5 jxm (Somogyi, 1986a ), which is obtained by 2 hour etching of the detector in 2.5 N, NaOH solution at 60°C in a constant temperature water bath to reveal the tracks. Alpha tracks were counted by an optical microscope at a magnification of 400X. The minimum (range of a-particle) track diameter, counted was 11 |j,m. Since the half-life of ^^^Ra is 1620 years and that of "^Rn is 3.82 days, it is reasonable to assume that an effective equilibrium (about 98%) for radium- radon members of the decay series is reached in about 3 weeks time. Once the radioactive equilibrium is established, one may use the radon alpha analysis for the determination of steady-state activity concentration of radium. The activity concentration of radon begins to increase with time T, after the closing of the Can, according to the relation: C^=cjl-e-'-') (2) Where CRS is the effective radium content of the sample. Since a plastic track detector measures the time-integrated value of the above expression i.e. the total number of alpha disintegrations in unit volume of the Can with a sensitivity K during the exposure time T, hence the track density observed is given by: P = KC ^, T, (3) 160 where Te denotes, the effective exposure time given by: T = T-V'(l-e^"^). • (4) In these measurements the exposure time T is 150 days. Finally, the "effective radium content" of a specimen in a Can (see Fig. 1) can be calculated by the formula: hA C,3(Bqkg-') = (5) KT. M where M is the mass of the solid sample in kg, A is the area of cross-section of the Can in m^; h is the distance between the detector and top of the solid sample in m. 161 4.8.3 Results and discussion Table 20 depicts the values of effective radium content of sand samples collected from Chhatrapur beach, Orissa, India. Table-20 Effective radium content in different sand samples Effective radium content Source of sample with S.No code CRa (Bq kg-') Samples from beach 1. Beach (B-7) 63.6 2. Beach (B-4) 68.8 3. Beach (B-20) 98.4 4. Beach (B-14) 106.1 5. Beach (B-9) 108.7 6. Beach (B-2) 110.1 7. Beach (B-8) 114.6 8. Beach (B-10) 132.7 9. Beach (B-3) 158.7 10. Beach (B-6) 183.4 11. Beach (B-17) 238.8 12. Beach (B-1) 305.3 13. Beach (B-19) 317.9 14. Beach (B-11) 389.8 15. Beach (B-16) 557.0 16. Beach (B-5) 587.9 17. Beach (B-13) 652.2 18. Beach (B-18) 654.6 19. Beach (B-12) 758.3 20. Beach (B-15) 773.5 Average value 319.0 S.D. 250.7 Rel.std.% 78.6 Samp es from river 1. River (R-1) 17.3 2. River (R-2) 18.4 3. River (R-3) 21.3 4. River (R-4) 29.5 Average value 21.6 S.D. 5.5 Rel.std.% 25.5 162 It is seen that values of effective radium varies from 63.6 Bqlcg'' to 773.5 Bqkg'^ with an average value of 319.0 Bqkg''. These values are lower than the values found for Brazilian beach sand (Veiga et. al, 2006).Table-22 also presents the value of effective radium content of sand samples collected from different rivers. It shows that the value of effective radium content varies from 17.3 Bqkg" ' to 29.5 Bqkg'' with an average value of 21.6 Bqkg"'. Average U concentration in the sand samples from Chhatarapur beach is 220 Bqkg"'wheares ^"ih concentration is 2500 Bqkg'' (Mohanty et al., 2004). The concentration of ^^"^Rn is expected to be small due to its very small half life and subsequent low exhalation rate. It is clear from Table-20 that the values of effective radium content in sand samples collected from Chhatrapur beach are higher than the values of effective radium content of sand samples collected from rivers. The higher values in the beach' sand samples may be attributed to the presence of radiogenic heavy- minerals in these samples. The heavy mineral assemblage includes ilmenite, garnet, sillimanite, rutile, zircon monazite, magnetite and minor amounts of hornblende, diopside, sphene, tourmaline, epidote and pyroxene, while the light sand minerals are quartz, feldspars and some mica. The ilmenite, garnet, sillimanite, rutile, zircon and monazites are present in the samples in decreasing order of abundance (Mohanty et. al., 2003). It is also clear from the Table that 13 samples have effective radium content below 370 Bqkg'' and 7 samples have effective radium content above 370 Bqkg''. The samples having effective radium content greater than 370 Bqkg'' are not advisable to be used in construction of dwellings as it is the limit for overall radium content as recommended by (OECD-79) for the safe use of building materials for dwellings. 163 References Ahmed, N.K., Abbady, A., El Arabi, A.M. Michel, R., El- Kamel, A. H., Abbady, A.G., 2006.Comparative study on the natural radioactivity of some selected rocks from Egypt and Germany. Indian J. Pure Appl. Phys. 44,209-215. Anjos, R., Veiga, R., Soares, T., Santos, A., Aguiar, J., Frascac, M., Brage, J., Uzeda, D., Mangia, L., Facure, A., Mosquera, B., Carvalho, C, Gomes, P., 2005. Natural radionuclide distribution in Brazilian commercial granites. Radiat. Meas. 39, 245-253. Azam, A., Prasad, R., 1989. Trace element analysis of uranium of soil and plant samples using fission track registration technique. J. Radioanal. Nucl. Chem., 133,199- 2002 Baba, A., 2002. 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Radiometric and Radon exhalation studies along Cu-U deposits, Singhbhum Shear Zone Jharkhand: Enviommental Implications. National Seminar on Mineral Based Industries- Proc. ppl87 Singh, A.K., Sengupta, D., Prasad, R. 1999.Radon exhalation rate and uranium estimation in rock samples from Bihar uranium and copper mines using the SSNTD technique. Appl. Radiat Isot 51,107-113. Somogyi, G., 1986a. Track detection methods of radium measurements. ATOMKI Preprint E/25. 167 Somogyi, G.,Hafez Abdel-Fattah,Hunyadi, I., Toth-Szilagyi., 1986b.Measurment of exhalation and diffusion parameters of radon in solids by plastic track detectors. Nucl. Tracks, 12,701-704. UNSCEAR, 1988. Sources and effects of ionizing radiation. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, New York. UNSCEAR, 1993. Sources and effects of ionizing radiation. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, New York. UNSCEAR, 2000. Sources and effects of ionizing radiation. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, NewYork. Veiga, R., Sanches, N., Anjos, R.M., Macario, K., Bastos, J., Iguatemy, M., Aguiar, J.G., Santos, A.M.A., Mosquera, B., Carvalho, C, Baptista, Filho, M., and Umisedo, N.K., 2006. Measurement of natural radioactivity in Brazilian beach sands. Radiat.Meas., 41,189-196. Vijayan, V., Behra, S.N, 1999. Naik A (Eds.) Enviommental management in coal mining and thermal power plants. Technoscience, Jaipur, pp.453-456. Yu, K. N.,Guan, Z.J., Stokes, M.J., Young, E.C.,1992. The assessment of natural radiation dose committed to Hong Kong people. Journal of Environmental Radioactivity 17,31-48 168 CHAPTER -5 fir Elffill '> I mm fi mmm CMTOl Chapter-V 5.1 Introduction Emission of radon per unit area per unit time is known as radon exhalation rate. Radon exhalation rates are two types: surface exhalation rate and Mass exhalation rate. Radon exhalation rate depends up on the radium concentration, in the material, emanation factor of radon from the material, porosity, permeability, density of the material, diffusion coefficient of the radon in the material, and moisture content and temperature. Radon exhalation rate is of prime importance for the estimation of radiation risk from various solid waste materials. The radon exhaling properties of porous materials, both naturally occurring like soil, coal, sand and rocks and man-made like mining wastes, fly ash and many building construction materials etc, have been the subject of several investigations (Jonassen, 1983; Karmadoost et al., 1988; Kumar et al., 2005). Radon, an a- inert radioactive gas whose predecessor is uranium is emitted from soil beneath the house and from building materials. Building materials are the main source of radon inside the dwellings. Because of low. level of radon emanation from these materials, long term measurements are needed. There is a need for developing simple and efficient measuring method and performing intensive studies for getting representative data about the radiation levels due to waste and building construction materials for predication of the level of radiation risk from various solid samples. Theory of the radon exhalation rate is the same whether the radon comes from the soil or from or from porous solid samples like coal, fly ash, sand and rocks etc. However, some features of the exhalation process are very different in two cases. For exhalation from the soil, the measurements are limited to exhalation from very small part of the exhaling surface, although the sample can be considered to be extended indefinitely in the exhalation direction. As far as radioactivity, porosity and permeability etc. are concerned, the sealing up results obtained for one small area to large area is only a question of homogeneity. Similar methods have also been used in case of building construction materials. Various waste materials produced by the thermal power plants, chemical and metallurgical industry have commonly been used in building construction materials. 169 "Sealed can technique" was used for the measurement of radon exhalation from solids has been widely used also in combination with several active measuring techniques (Stranden, 1983; Somogyi et al., 1986). In all these techniques where a limited amount of emanating specimen is used in a closed container, it is expected that the exhalation rate depends upon the material and its amount as well as on the geometry and dimension of the Can. The reduction in radon exhalation from a sample under steady state condition in a sealed can is reported and is attributed to "back-diffusion" phenomenon. It is worth mentioning here that it is difficult to predict the radon exhalation rate from the concentration of decay series isotopes in a sample as the exhalation depends amongst other things, on the texture and grain-size composition as well as on the moisture content, etc. Health risks are especially high in the area downward of the power plant. Being very minute, fly ash particles may tend to remain airborne for long periods leading to serious health problems as the airborne ash can enter the lungs through inhalation and may stick to lung tissues. Due to higher radon emanating power, the lung tissues may be irradiated with a- particles from radon progeny to a high degree, increasing the possibility of lung cancer. These radionuclides in the fly ash may migrate from the waste disposal site to the underlying ground water body and may also accumulate in the top soil giving sufficient chances for the radionuclides to become enriched in the soil. Thus it is quite important to estimate the radiation risk to the population from the radon exhalation rate. 5. 2 Materials and methods 5.2.1 Measurement of radon exhalation rate Radon exhalation rate is of prime importance for the estimation of radiation risk from various materials. "Sealed Can Technique" (Fleischer and Morgo-campero 1978; Mahur et al., 2008) was adopted for radon exhalation measurements: (i) Radon exhalation measurements in coal, fly ash, rocks, soil, sand and other building construction materials used in our country. 170 All the samples collected were grinded, dried and sieved through a 100 mesh sieve. Equal amount of each sieved (100fj,m grain size) sample (lOOgm) was placed at the base of the Cans of 7.5 cm height and 7.0 cm diameter similar to those used in the calibration experiment ( Singh et al„ 1997). LR-115 Type II plastic track detector (2 cm x 2 cm) was fixed on the top inside of the cylindrical Can (details given in chapter II). As fly ash is now frequently used for the formation of bricks, it was thought worthwhile to study the effect on the radon exhalation rates by adding different amount of fly ash. A separate experiment was performed to measure exhalation rate of radon from homogenous mixture of (i) fly ash and soil and (ii) fly ash and cement. For this purpose different percentage of fly ash was introduced into the soil and cement keeping the total weight of the sample constant. All the samples were dried and sieved through a 100 mesh sieve before mixing homogenously and the samples were placed in Cans for radon exhalation measurements (ii) Radon exhalation rates different types of bricks, cement bricks (hollow and solid), plastered bricks, flooring materials like mosaic, Kadappa, marble, granite, ceramic tile, floorconcrete , etc. Plastic "Can" of known dimension (7.5cm height and 7.0cm diameter) was sealed by plasticin to the individual building material (details given in chapter II). In each Can a LR-115 type 11 plastic detector (2 cm x 2 cm) was fixed at the top inside of the Can. The Cans were sealed for 100 days. The lower sensitive part of the detector in both the cases is exposed freely to the emergent radon from the sample in the Can so that it could record the tracks of alpha particles resulting from the decay of radon in the remaining volume of the Can and from Po deposited on the inner walls of the Can. Radon and its daughters reach equilibrium in about four hours and hence the equilibrium activity of emergent radon can be obtained from the geometry of the Can and the time of exposure. After the exposure the detectors were etched in 2.5 N NaOH at 60° ± 1° C for a period of 90 minutes in constant temperature water bath for revelation of tracks. The resulting a- particle tracks were counted using an optical microscope (magnification 400x). The activity was obtained from the track density in the etched detectors using the calibration factor of 0.056 track cm'^ d''(Bq m"'')'' obtained from our earlier calibration 171 experiment (Singh et al., 1997). Following expression gives the exhalation rate (Fleischer and Morgo-campero 1978; Khan et al., 1992; Mahur et al., 2008): „ CVA ,,, Ex = -^ =r (1) T4-i{.--l} Where 9 1 Ex - Radon exhalation rate (Bq m" h' ) C - Integrated radon exposure as measured by LR-115 type II plastic track detector (Bq m''' h) V - Effective volume of the Can (m^) X - Decay constant for radon (h"') T - Exposure time (h) A - Area covered by the Can (m ) 5.2.2 Indoor internal exposure due to radon inhalation The risk of lung cancer from domestic exposure of ^^ Rn and its daughters can be estimated directly from the indoor inhalation exposure (radon)-effective dose. The contribuition of indoor radon concentration from building construction materials can be calculated from the expression (Nazaroff and Nero, 1988). C =^^^ (2) -J Where, CRO, EX,S, V, ^v are radon concentration (Bq m'), radon exhalation rate (Bq m"^ h''), radon exhalation area( m^), room volume (m'') and air exchange rate (h"') respectively. In these calculations, the maximum radon concentration from the building material was assessed by assuming the room as a cavity with S/V= 2.0m' and air exchange rate of 0.5 h''. The annual exposure to potential alpha energy Ep, (Effective dose equivalent) is then related to the average radon concentration CRO by the following expression: 172 170x3700 ^ ^ Where, Can is in Bq m'^; n, the fraction of time spent indoors; 8760, the number of hours per year and 170, the number of hours per working month and F is the equiUbrium factor for radon. Radon progeny equiUbrium is the most important quantity when dose calculations are to be made on the • basis of the measurement of radon concentration. Equilibrium factor F quantifies the state of equilibrium between radon and its daughters and may have values 0< F <1. The value of F is taken as 0.4 as suggested by UNSCEAR (2000). Thus the values of n = 0.8 and F = 0.4 were used to calculate Ep. From radon exposure, the indoor inhalation exposure (radon)-effective dose were estimated by using a conversion factor of6.3 mSv/WLM (ICRP, 1987). 5.3 Results and discussion 5.3.1 Measurement of radon exhalation rate in coal and fly ash samples Coal is a technologically important material used for power generation. Its cinder (fly ash) is used in the manufacturing of bricks, sheets, cement, land filling etc. Coal and its by products often contain significant amounts of radionuclides, including uranium which is the ultimate source of the radioactive gas radon. Burning of coal and the subsequent atmospheric emission cause the redistribution of toxic radioactive trace elements in the environment. Thermal power generation contributes more than 70% of the power generation in India. Indian Coal is of bituminous type with 55-60 % ash content amounting to 100 million tons of fly ash per year (Vijayan and Behra, 1999). Like other natural materials, coal contains U, Th, and K radionuclides which may be concentrated in the fly ash by thermal power plant combustion. Also, coal combustion may enhance the natural radiation in the vicinity of the thermal power plant through the release of the radionuclides and their daughters in the surrounding ecosystem such as the surface soil. Due to diverse uses of fly ash in building materials, as under ground cavity filling material and in the production of cement etc., fly ash has become a subject of worldwide 173 interest in recent years. Radon exhalation rate from fly ash is of prime importance for the estimation of radiation risk. Earlier studies (Mishra, 1991) on coal and fly ash have shown that Indian coals contained 1.8- 6.0 ppm ^^^U and 6.0 -15.0 ppm of ^^^Th. Recent studies have indicated as high as 50 ppm ^•'^Th and 10 ppm of ^^^U in the pond ash generated from coal combustion (Mandal and Sengupta, 2003). Radiation risk from fly ash is of importance since if used in construction materials it may raise the concentration of airborne indoor radioactivity to unacceptable levels, especially in places having low ventilation rates (Rawatet al., 1991 and Khan et al., 1992). In the present study, radon exhalation rates from the coal and fly ash samples collected from the thermal power stations at Kolaghat, Durgapur, Bandel and Kasimpur situated in West Bengal and Uttar Pradesh states of India have been measured to estimate their enhancement in fly ash due to coal combustion usmg "Sealed Can Technique" having LR-115 type II detectors. Fly Ash has a vast potential for use in agriculture as an amendment specially due its physical condition which are conducive for plant growth as well as due to the presence of macro and micronutrients in it. Good amounts of research has already been done all over India and abroad on the yield of agricultural crops using fly ash and have found a yield increase of 15 to 25% with application fly ash. However, 100% and even higher increases in yield have also been reported in some cases. Presence of heavy/ toxic trace elements in Fly Ash has been a cause of concern to many. Use of fly ash in agriculture has to take note of the possible negative impacts, if any, due to the presence of these trace elements. Various reports regarding Indian experiences indicate that the impact of heavy/ toxic trace elements present in fly ashes, on agriculture produce, plants grown on it is not alarmmg and it is being reported that the impact is within the normal accepted range. The results for the values of the track density, radon activity and radon exhalation rates from the coal and fly ash samples collected from Kolaghat, Durgapur, Bandel situated in the state of West Bengal and Kasimpur in Uttar Pradesh, India, are presented in Tables 1-4. Table 1 presents the results for coal samples from Kolaghat thermal Power Plant along with the average value for nine coal samples of Kasimpur thermal power plant. Table 2 presents the results for fly ash. 174 Table-1 Radon activity concentration, radon exhalation rate and indoor inhalation exposure (radon)-effective dose in coal samples from Kolaghat thermal power plant (West Bengal), India Indoor inhalation Radon exhalation exposure (radon)- Sample Radon activity rate effective dose (Bq m-^) (mBq m-^h-^) (MSV y-') C-1 1960 ±69 700 ± 27 79 C-2 2740 ±123 980 ±38 110 C-3 980 ± 44 350±13 39 C-4 860 ± 39 310±12 35 C-5 2860 ±128 1030 ±40 116 Average Value 1880 670 76 S.D. 840 300 34 Rel.S.D.% 44.7 45.5 44 Coal Samples from KTPP* (Average 3180 1170 128 value- 9 samples) KTPP - Kasimpur thermal power plant 175 Table-2 Track density, radon activity and radon exhalation rate in fly ash samples from Kolaghat thermal power plant (West Bengal) India Indoor Radon inhalation Track density Radon activity exhalation rate exposure Sample (Trcm'^d') (Bqm-^) (mBqm"^h"') (radon)- effective dose (liSvy-') 203 ±7 3620 ±126 1302 ±45 146 FA-1 FA-2 190 ±7 3390 ±120 1220 ±42 136 FA-3 233 ±8 4150±135 1491 ±48 167 FA-4 197 ±7 3520 ±123 1260 ±45 142 FA-5 184 ±7 3280 ±120 1182 ±42 124 FA-6 171 ±6 3050 ±114 1100 ±42 123 FA-7 229 ±8 4090 ±132 1470 ± 48 165 FA-8 174 ±6 . 3100±117 1120 ±42 125 FA-9 241 ±8 4310±135 1550 ±51 174 FA-10 219±7 3910 ±129 1400 ±48 157 Average value 204 ± 7 3640 ± 125 1310 ± 45 146 S.D. 24 ±0.7 430 ±7 150 ±3 18 Rel. S.D. % 12 ±10 12 ± 6 11.5 ±7 12 176 In coal samples from Kolaghat radon activities were found to vary from 860 ± 39 to 2860 ± 128 Bq m"'' with an average value of 1880 Bq m"^, whereas the radon exhalation rate varied from 310 ± 12 to 1030 ± 40 mBq m"^ h'' with an average value of 670 mBq m" h'. While in fly ash samples, radon activity is found to vary from 3050 ± 114 to 4310 ± 135 Bq m'^ with an average value of 3640 ± 125 Bq m'^, whereas the radon exhalation rate varied from 1100 ± 42 to 1550 ± 51 mBq m'^ h'' v^th an average value of 1310 ± 45 mBq m"^ h'\ Values of indoor inhalation exposure (radon) -effective dose for the samples from Kolaght thermal power plant varies from 35 to 116 fiSv y' with an average value 760 )aSv y'' in coal samples whereas in fly ash samples it is foimd to vary from 123 to 174 \xSv y'' with an average value 146 ^Sv y''. Figures 1 and 2 show the variation of radon exhalation rate with ^^*U concentration (taken from chapter 4) in coal and fly ash samples from Kolaghat thermal power plant. There appears to be the positive correlations between radon exhalation rate and uranium concentration. Values of the radon activity and radon exhalation rates in the fly ash samples collected from Durgapur Thermal power plant are presented in Table-3. Radon activities were found to vary from 1005.1 ± 29.1 to 1308.3 ± 43.3 Bq m"^ with an average value of 1132.9 ± 39.1 Bq m"^, whereas the radon exhalation rate varied from 360 ± 10.4 to 470 ± 15.5 mBq m"^ h"^ with an average value of 406.8 ± 14.0 mBq m h". Values of indoor inhalation exposure (radon) -effective dose in these samples varies from 42.5 to 55.4 |iSv y"' with an average value 47.8 mSv y''. Figure- 3 shows the variation of radon exhalation rate with ^"'^U concentration (taken from chapter 4) in these fly ash samples. There seems to be positive correlation between them. 177 I9UU ^^ • REdonesdialationrate; ^ Linearfit j «f 1250 E • a O" y/ QQ .A^ g1000 • / >iiii * B / ^ X t: 750 / c ^m _o X '^ y (Q X J 500 • / • X X f 0 c ^_^ • r * o 250 y^ •o ' ^ , , £L • 10 20 30 40 50 60 Uraniun Concentration (Bq kg'^) Figure- 1. Radon exhalation rate versus uranium concentration in coal (Kolaghat) samples 178 JiWU ^.^ • Radon exhalation rate . T - Linear fit f 1750 E • " f 1500 • • 3 • 2 1250 c o • '^ • • 75 1000 - X o o 750 n 100 105 110 115 120 125 Uranium Concentration (Bq kg-i )i Figure- 2 : Radon exhalation rate versus uranium concentration in fly ash (Kolaghat) samples 179 Table-3 Track density, radon activity and radon exhalation rate in fly ash samples from Durgapur thermal power plant (West Bengal), India Indoor inhalation Track Radon Radon exhalation exposure (radon)- Sample density activity rate effective dose (Cm'^d-*) (Bq m^^) (mBqm-^h*) (nSvy-') IIT-Dl 62.1 ±2.2 1109.1 ±39.7 399 ±14.3 47.1 IIT-D2 63.7 ±2.2 1138.3 ±40.3 409 ±14.5 48.2 IIT-D3 59.6 ±2.1 1064.2 ±38.9 382 ±13.9 45.0 IIT-D4 73.1 ±2.4 1304.9 ±43.2 468 ±15.5 55.2 IIT-D5 61.3 ±2.2 1094.3 ±39.5 394 ±14.2 46.5 IIT-D6 73.3 ± 2.4 1308.3 ±43.3 470 ±15.5 55.4 IIT-D7 56.2 ±1.6 1005.1 ±29.1 360 ±10.4 42.5 IIT-D8 68.2 ± 2.3 1218.4±41.7 438 ±14.9 51.6 IIT-D9 60.3 ±2.1 1076.6 ±39.2 386 ±14.1 45.5 IIT-Dl 0 56.6 ±1.9 1010.3 ±35.6 362 ±12.7 42.7 Average 63.4±2.1 1132.9±39.1 406.8±14 47.8 Value S.D. 5.9 ±0.2 104.4 ±3.9 37.7 ±1.4 4.4 Rel. 9.2 ±9.5 9.2 ±9.9 9.3 ± 10.0 9.2 S.D.% 180 1000 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I t Radon exhalaUon rate • Li near fit E 800 OQ E ^600 ? c 1400 (0 X Q> §200 •D j-i. • • • 80 90 100 110 120 130 140 Uranium Concentration (Bq kg'^) Figure- 3. Radon exhalation rate versus uranium concentration in fly ash samples from Durgapur thermal power plant 181 The values of the radon activity and radon exhalation rates in the fly ash samples from Bandel Thermal Power Plant (BTPP) are presented in Table-4 Radon activities were foimd to vary from 953.6 ± 36.8 to 1414.3 ± 44.8 Bq m"^ with an average value of 1055.5 db 38.6 Bq m'^, whereas the radon exhalation rate varied from 342.8 ± 13.2 to 508.5 ± 16.1 mBq m'^ h'' with an average value of 379.5 ± 13.8 mBq m'^ h"'. Values of indoor inhalation exposure (radon) -effective dose in these samples varies from 40.4 to 60.0 fiSv y'' with an average value 44.8 |aSv y'^ Figure -4 shows the variation of radon exhalation rate with ^^^U activity concentration. There is a positive correlation between them. Table 5 presents the results of the measurements along with the results of the previous measurements of our group.for average radon exhalation rate in fly ash samples from different thermal power plants in India. It can be observed that coal and fly ash from the Kolaghat Thermal Power Plant (KTTP) has higher values of radon activity and radon exhalation rate compared to other power plants in India. It is worth mentioning that it is difficult to predict the radon exhalation rate from the concentration of uranium or its decay series products in a sample, since the radon exhalation rate depends also on the texture and grain size composition. 182 Table-4. Track density, radon activity and radon exhalation rate in fly asli samples from Bandel thermal power plant (West Bengal), India Track Radon activity Radon exhalation Indoor inhalation Sample density (Bqm-3) rate exposure (radon)- (TrCm-^d-') (mBqm-^h"') effective dose (nSv y-') BTPP-1 79.2 ± 2.5 1414.3 ±44.8 508.5 ±16.1 60.0 BTPP-2 59.8 ± 2.2 1068.6 ±39.0 384.2 ±14.0 45.3 BTPP-3 57.3 ±2.1 1022.9 ±38.2 367.7 ±13.7 43.4 BTPP-4 44.5 ±1.9 794.6 ±33.6 285.7 ±12.1 33.7 BTPP-5 64.3 ±2.3 1148.6 ±40.3 412.9 ±14.5 48.7 BTPP-6 55.2 ±2.1 985.7 ±37.5 354.4 ±13.4 41.8 BTPP-7 53.4 ±2.1 953.6 ±36.8 342.8 ±13.2 40.4 Average 59.1 ±2.2 1055.5 ±38.6 379.5 ±13.8 44.8 S.D 9.9 ±0.2 178.1 ±3.2 64.0 ± 1.1 7.6 Rel. Std.% 16.8 ±9.0 16.9 ± 8.3 16.9 ± 8.0 17.0 183 600 I I I I I I I I I I I I I I I I I I I I I I Redon exhalation rate N Linear fit • E 500 m E 0^400 c o 1 300 to X 0 O 200 100 • • • • ' I I I I I I I j-i. 25 50 75 100 125 150 175 Uranium Concentration (Bq 1^'^) F^ure- 4. Radon exhalation rate versus uranium concentration in fly ash samples from Bandel thermal power plant 184 Table-5 Average radon exhalation rate in fly ash samples from different thermal power plants in India. Average radon exhalation rate (± S. D.) Name of thermal power plant (mBq m"^ h"') Kasimpur Aligarh (U.P.) 275.3 ±45.7 Kasimpur Aligarh (U.P.) 1090 ±270 Parichha, Jhaiisi (U.P.) 257.6 ±48.7 Obra, Mirjapur (U.P.) 239.9 ± 24.8 Koiaghat (W.B ) 1310±150 Durgapur ( W.B.) 406.8 ± 37.7 Handel (W.B.) 379.5 ± 64.0 185 The effect of fly ash as an additive to building materials has been studied by several groups and conflicting results have been reported by different workers (Stranden, 1983; Maraziotis, 1985 ) reported a reduction in radon exhalation in concrete with fly ash as additive. The data of Siotis and Wrixon, 1983 on cement with different amount of fly ash additive in it contradict these results. (Ulback et al., 1983; Karmadoost et al., 1988) conclude that no significant change has been found in cement and soil samples after the addition of fly ash. To investigate any statistically reliable correlation on the use of fly ash additive, we have applied t-test to our measurements. The results for homogeneous mixtures of (i) cement and fly ash and (ii) soil and fly ash in different proportions are presented in Table-6. Gradual increase has been observed in the samples having fly ash as an additive in cement samples whereas reduction is observed in soil samples after the addition of fly ash. However, experimental values for mixtures of ash and cement are more than the values expected fi-oma n arithmetic computation based on relative proportions of ash and cement whereas opposite trend is observed for mixtures of ash and soil. This shows that values for mixture increases if the additive has greater exhalation rate that the base material and decrease if the values for additive is less. This may be due to the emanation powers of different materials and perhaps some difference in the grain size of the materials. The observation can be utilized in suppressing the radon emanation. 186 Table-6 Radon exhalation rate from cement and soil with different amount of fly ash (Expressed in % by weight) substituted into the samples of equal total weight. Radon Radon Expected Fly ash Track density activity exhalation values from Sample. additive (cm-^d-*) (BqmO rate(mBqm' an arithmetic (%) mean 1. Cement ACO 0 26.8 ±1.S 482 ± 26 173±9 - ACl 10 49.9 ±2.0 891 ±3 6 320 ± 1 3 207 AC2 20 6S.9±2.3 1176 ±41 422 ±15 241 ACS 30 67.S ± 2.3 1206 ± 42 433 ±15 275 AC4 40 69.2 ± 2.4 1235 ± 42 443 ±16 310 ACS SO 79.1 ±2.S 1412 ±45 507 ±17 344 2. Soil ASO 0 100.9 ±2.8 1803 ±51 648 ±18 - ASl 10 91.3 ±2.7 1630 ±49 586 ±18 634 AS2 20 75.5 ±2.S 1348 ±44 484 ±16 621 . ASS 30 72.24 ± 2.4 1290 ±43 463 ±15 608 AS4 40 65.16 ±2.3 1163±41 418±15 595 ASS 50 60.3 ± 2.2 1076 ±39 387 ±14 582 187 5.3.2 Radon exhalation in rock samples The central part of Singhbhum shear zone in Jharkhand state situated in eastern India, between Jaduguda-Bhatin-Nimdih, Narwapahr-Garadih-Turamdih is rich in uranium. Presence of uranium in the host rocks and the prevalence of a confined atmosphere within mines could result in enhanced concentration of radon (^^^Rn) gas and its progeny. Inhalation of radon daughter products is a major contributor to the radiation dose to exposed subjects. Details of.the geology of Singhbhum shear zone are given in chapter FV. For the study rock samples were collected from different places of Jaduguda uranium mines in Singhbhum shear zone. Sealed Can technique using Solid State Nuclear track detectors was used for the measurement of radon exhalation rates. Values of radon activities and radon exhalation rates from the rock samples are given in Table-7. 188 Table-7 Radon exhalation rate in rock samples from Jaduguda uranium mines in Singhbhum shear zone, Jharkhand. Radon exhalation Track density Radon Activity Sample rate (Bqm-^) (Bq m-^ h') JADl 1665.8 ±11.5 29746.5 ± 205.3 10.7 ±0.07 JAD2 2131.4±13.0 38061.4 ±232.2 13.7 ± 0.08 JAD3 1752.5 ±11.7 31294.9 ±209.7 11.3 ±0.08 JAD4 1877.1 ±12.2 33466.3 ±217.5 12.0 ±0.8 JAD5 1837.1 ±12.1 32806.0 ±216.5 11.8 ±0.07 JAD6 2015.9 ±12.7 35994:9 ±226.7 12.9 ±0.08 JAD7 655.2 ± 7.2 11687.1 ±128.5 4.2 ±0.05 Average:- 1705±11.5 30436.7 ±205.2 10.9±0.07 S.D.:- 452.2 ±1.8 8076.3 ±32.5 2.9 ±0.01 Rel. Std. (%):- 26.52 ± 15.7 26.53 ± 15.8 26.60 ± 14.3 189 20 I I I I I I I I I I I I I I I I I I I I I # Radon e9(hala(tion fete Linear fit CM 15 QQ I c 10 o 1 (0 X 0) c o •o (0 '•'''••'' 0 10000 20000 30000 40000 SOOOO lkaniiiTiConoenbation(Bq kg"*) F^ure- 5 : Radon exhalation rate versus uranium concentration in rock samples 190 Radon activities are found to vary from 11687.1 ± 128.5 to 38061.4 ± 232.2 Bq m"'' whereas the radon exhalation rate varies from 4.2 ± 0.05 to 13.7 ± 0.08 Bq m"'^ h"'. Figvire- 5 shows the variation of radon exhalation rate with ^^*U concentration (taken from chapter 4) in these samples. There is positive correlation between U-concentration and radon exhalation rate. The high radon exhalation rates in the range of- 4.2 -13.7 Bq m'^ h'' are in broad agreement with our previous preliminary studies from Jaduguda U- mines (Singh et al., 1999) and is expected due to the presence of uranium in highly weathered schist and apatite magnetite rocks. Ground water flow, solution movement and the presence of folds and fractures in them may further enhance the emanation. Radon exhalation rate strongly depends on the parameters like (i) uranium content (ii) presence of enriched soil or rock and (iii) the permeability, moisture content, relative humidity and associated meteorological parameters. Although radon levels tend to be very high in the confined spaces of underground drifts, elevated radon levels are also found in open pit mines and around U-mill tailings. From open pit mines the radioactive emissions are radioactive fugitive dust and radon gas. High values of radon exhalation rates in the rock samples from different parts collected from Jaduguda U-mines of the Singhbhum shear zone have been found and are characterized by their higher concentration of uranium. Although a positive correlation has been found between the radon exhalation rate and uraniimi concentration shown in Figure-5, there is heterogeneous distribution of U which is very common in crustal rocks. Computed radiological data indicates that the region is not safe and may pose significant radiological threat to the population. 5.3.3 Radon exhalation rate measurement in soil samples The source of radon in indoor air are: (i) soil and bedrock beneath a building (ii) building material and the (iii) the tap water. If the soil above the bed rock has an enhanced content of U, the soil becomes a potential source of radon gas in the soil air. Radon transport from soil to the atmosphere may be considered as occurring in two main steps: firstly the emanation process and secondly migration through the soil. The emanation process involves the transformation of the radium atom to a radon atom in the 191 mineral grain and its subsequent escape from the mineral grain into the inter-grain pore space from where it can migrate to the atmosphere. The measurement of radon exhalation is important for the estimation of radiation risk and has been the subject of interest of research scientists all over the world. Jharkhand State is rich in minerals and is called as store house of minerals. Soil samples were collected from Rajmahal area, famous for coal and quartz mines. In the present study radon exhalation rate from these soil samples are measured for the estimation of effective radiation dose to assess the radiation risk to the inhabitants. "Sealed Can technique" was used for the radon exhalation measurements. In such measurements it is expected that the exhalation rate depends upon the material and the geometry and dimension of the Can and as well as on the material and its amovmt. Also measurements of radon activity, radon exhalation rate and indoor inhalation exposure (radon)-effective dose m soil samples collected from different locations in the neighborhood of Mathura refinery, Kasimpur thermal power plant and Kolaght thermal power plantwere carried out. Soil samples were also collected from inside the refinery and township at Mathura and Kasimpur thermal power plant (U.P.) and four soil samples from 5-6 meters away from Kolaghat thennal power plant in the direction East, West, North and South. Mathura refinery was commissioned in 1982 as the sixth refinery in the fold of Indian Oil Corporation and with an original capacity of 8.0 MMTPA. Located strategically between the historic cities of Delhi and Agra, the refinery at Mathura is situated in the mythical and mystical land of Lord Krishna. Later the capacity of Mathura refinery was increased to 7.5 MMTPA by systematically debottlenecking and revamping. With its Fluid Catalytic Cracking Units (FCCU), the refinery mainly produces middle distillates for Northern India supplied though a 760km long product pipeline to Jalandhar in Punjab via Delhi (MJPL) and 100km long Mathura Tundla Pipeline (MTPL). A Vis- breaking unit was commissioned in 1982 and Soaker drum technology was implemented in VBU in the year 1993. The two-stage desalter was commissioned in 1998 in order to improve the on-stream availability of the crude distillation unit. In the same year new Continuous Catalytic Reformer Unit (CCRU) Catalytic Reformer Unit (CCRU) for production of unleaded 192 gasoline was added. The First hydrogen generation unit (HGU-I) commissioned in 1999 along with first Diesel Hydro-desuliurisation unit (DHDS) for production of HSD with a low Sulfur content of 0.25% wt (max). A once through Hydro-cracker unit was commissioned in July' 2000 for increased middle distillates production. For supplying EURO-III grade auto fuels, viz, EURO-III HSD and EURO-III MS to National Capital Territory (NCT) and National Capital Region G^CR), a Diesel Hydro-treating unit (DHDT) and MS quality up gradation unit consists of NHDT and PENEX along with FCCU Gasoline splitter and 2nd Hydrogen generation unit (HGU-II) commissioned in 2005. The present capacity of the refinery is 8.0 MMTPA and regularly receives crude oil through the 1870 km long Salaya Mathura Pipeline (SMPL). Over the years Mathura Refinery has systematically synchronized technology with ecology with constant care for the surrounding environment. Its close proximity to the magnificent wonder Taj Mahal adds to the responsibility towards a cleaner Environment. Kasimpur thermal power plant is situated in the plains of the state of Uttar Pradesh and the wastes are discharged into the upper Ganges canal. Kolaghat thermal power plant is situated in the Midnapur district of West Bengal and near Mecheda railway station on the South-Eastem Railv/ay route. It is 59 km away from Kharagpur in the ENE direction and 60kmWSWofKolkata. Radon enters the air contained in soil by diffusion from soil particles or some times from rich ground water at greater depths. Diffusion rate is highly dependent on the moisture content of soil and diffusion coefficient. Concentration of radon in soil near earth's surface is affected by several meteorological factors (pressure, humidity, rainfall and temperature). These factors also influence the radon exhalation to the atmosphere. There is a large variation in radionuclide activity and exhalation rates. The value of radon activity, radon exhalation rates and indoor inhalation exposure (radon) -effective dose from the soil samples collected from Rajmahal region of the state of Jharkhand are given in Table -8. Radon activities are found to vary from 8502.8 ± 92.7 to 21760.0 ± 387.3 Bq m'^ with an average value of 11886.77± 198.9 Bqm'^ while the radon exhalation rate varies from 3.05 ± 0.03 to 7.82 ± 0.13 Bqm'^ h"' with an average value of 5.74 ± 0.07 Bqm"^ h"'. Values of indoor inhalation exposure (radon) -effective dose in soil samples varies from 193 335.5 to 860.2 nSv y'' with an average value 631.8 \xSv y''. Figure-6 shows the variation of radon exhalation rate with U-concentration in the soil samples studied here.It shows a positive correlation between the two. The values of radon activity, radon exhalation rate and Indoor inhalation exposure (radon)-effective dose at different locations at Mathura refinery, Kasimpur thermal power plant (U.P.) India and Kolaghat thermal power plant (W.B.) India, are shown in Table- 9. Gradual decrease in radon activity, radon exhalation rate and indoor inhalation exposure (radon)-effective dose has been observed in the soil samples v^th the distance from the refinery at Mathura or thermal power plant at Kasimpur. 194 Table-8 Radon activity, exhalation rate and effective dose equivalent in soil samples collected from Rajmahal region of the state of Jharkhand Indoor inhalation Radon exposure Sample Radon Activity Description Exhalation (radon)- No. (Bqm-') rate(Bqm'^h'^) effective dose (nSv y-') 1 Deoghar 18914.28±111.6 6.79 ± 0 .04 746.9 2 Madhupur 20337.14 ±229.8 7.31 ±0.08 804.1 3 Shahibganj 21760.0 ±387.3 7.82 ±0.13 860.2 4 Crodda 8502.8 ± 92.7 3.05 ±0.03 335.5 5 Dumka 9345.71 ± 154.2 3.35 ±0.05 368.5 6 Pakur 18502.85 ±220.2 6.65 ± 0.08 731.5 7 Jamtara 17582.85 ±211.0 6.32 ±0.07 695.2 8 Barawaha 12968.57 ±184.2 4.66 ± 0.06 512.6 Average value 11886.77± 198.9 5.74 ±0.07 631.8 S.D. 7362.74±85.3 1.70 ±0.03 187.2 Rel. Std.% 61.94±42.9 • 29.61 ±42.9 29.6 195 10 llllllll I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I, • REdon exhalation rate: Linear fit { 8 A 6 5 j5 I(0 4 c 3 o 2 & *! r, , , , I , , , , I , , , , I , , , , I . . , , I , , , , I , , , , I , , , ,' 500 750 1000 1250 1500 1750 2000 2250 2500 UaniiinOonoenbBtion (Bq kg'^) Figure-6. Radon exhalation rate versus uranium uoncentration in soil samples collected from Rajmahal region of the state of Jharkhand 196 Table -9 Radon activity, radon exhalation rates and effective dose in soil sample collected from various distances from Matura Refinery, Kasimpur and Kolaghat thermal power plants Indoor inhalation Radon Exhalation Radon Activity exposure (radon)- Location Rate (Bqm-^) effective dose (mBqm-^h-*) (nSvy-'> Inside Mathura 4512.9 ±79.9 1622.5 ±28.7 191.3 refinery Outside Mathura 3891.4 ±74.3 1399.1 ±26.7 165.0 refinery Township Mathura 3840.0 ±73.7 1380.6 ±26.5 162.8 refinery Inside Kasimpur 4262.3 ± 78.0 1533.1 ±28.1 180.8 thermal power plant Outside Kasimpur 3981.4 ±75.2 1431.4 ±27.0 168.8 thermal power plant Township Kasimpur 3214.3 ±67.5 1155.6 ±24.3 136.3 thermal power plant East (5-6 Meters 2851.4 ±63.9 1025.2 ±23.0 120.9 from *KTPP) West (5-6 Meters 3152.9 ±66.8 1133.5 ±24.0 133.7 from KTPP) North (5-6 Meters 4440.0 ± 79.5 1596.3 ±28.6 188.2 from KTPP) South (5-6 Meters 2494.3 ± 59.6 892.4 ±21.3 105.2 from KTPP) *KTPP- Kolaghat thermal power plant 197 5.3.4 Radon exhalation in sand samples In India there exists some natural HBRA's due to monazite sand bearing placer deposits along its long coast line in south India such as Ullel in Kamatak (Radhakrishna et al., 1993) Kalpakkam in Tamilnadu (Kanan et al, 2002), coastal parts of Tamilnadu and Kerala and the southwestern coast of India (Mishra, 1993; Sunta, 1982. Recently Mohanty et al., 2004a, 2004b have carried out natural radioactivity measurements in the newly discovered HBRA on the eastern coast of Orissa and higher levels of uranium, thorium and potassium ai-e observed in the sand samples. Chhatrapur beach placer deposit and Erasama beach placer situated in a part of the eastern coast of Orissa, are newly discovered high natural background radiation area (HBRA) in India. Radon exhaling properties of porous materials are of prime importance for the estimation of radiation risk and have, been the subject of several investigations (Jonassen 1983; Karmadoost et al., 1988; Kumar et al., 2005; Mahur et al., 2005). The correlation between the uranium concentration and the radon emanation potential of the source material is required for radon risk. The sand is the basic ingredient used in construction materials in India. By mixing it vnih cement, sand is commonly used as a binding material for fired clay and fly ash bricks for the construction of walls and also as a plastering material. It is also used in the preparation of concrete. Thus it is quite important to find its radon emanation potential to have an estimation of radiation risk to the habitants. In the present study radon exhalation rate measurement from the sand samples of the Chhatrapur and Erasma beach placer deposit have been carried out for finding its correlation with uranium concentration and the estimation of radiation risk. The sand samples containing heavy minerals, were collected from Chhatrapur and Erasama region by the grab sampling method at an interval of- 1 Km. The values of radon activity, radon exhalation rate and uranium concentration in the sand samples collected from Chhatrapur beach placer deposit are presented in Table 10. Radon activity is found to vary fromll77.1 ± 40.9 to 4551.4 ± 80.6 Bq m"^ with an average value of 2116.6 ± 53.7 Bq m''' whereas the radon exhalation rate varies from 423.2 ± 14.7 to 1636.3 ± 29.0 mBq m'^h'' with an average value of 763.9 ± 19.4 mBq m"^ 198 h"'. Uranium concentrations varies from 4.9 to 48.5 ppm with an average value 17.8 ppm. Figure -7 shows correlation between the radon exhalation rate and uranium concentration. There is a positive correlation between them. Values of indoor inhalation exposure (radon)-effective dose in these sand samples estimated from exhalation rate varies from 49.9 to 193.0 ^Sv y"' with an average value of 90.1 fiSv y''.The values of radon activity and radon exhalation rates in the sand samples collected from Erasma beach placer deposit are presented in Table- 11. U-concentration in these samples as measured by our collaborators (Mohanty et al, 2004a) are also given in the Table. Radon activities are found to vary from 1471 ± 46 to 4686 ± 87 Bq m"^ with an average value of 3349 ± 68 Bq m"^ while the radon exhalation rate varies from 529 ± 16 to 1685 ± 31 mBq m'^ h'' with an average value of 1204 ± 25 mBq m'^ h'V It can be observed from the results that the radon exhalation rate varies appreciably from one sample to another. In our previous measurements (Khan et al., 1992) in some sand samples from the normal back ground area of India average radon exhalation rate has been found to be 108 mBq m''^ h"'. Present values are much higher than this value and the values for other building materials such as soil, cement, clay bricks, concrete, marble, fly ash, gypsum etc. estimated from our earlier studies (Khan et al, 1992; Kumar et al., 2005) shown in Table-12. It is expected that radon exhalation should depend on the uranium concentration in the samples. But it is woi-th mentioning that it is difficult to predict the radon exhalation rate from the concentration of uranium or its decay series products in a sample, since the radon exhalation rate depends also on the texture and grain size concentration. To investigate the correlation between the radon exhalation rate and the uranium concentration in the samples, variation of radon exhalation rate with uranium concentration is plotted in Figure-8. There is a positive correlation between the two as also observed in other cases. 4 199 Table 10. Radon activity, radon exhalation rates and effective dose in bulk sand samples collected from Chhatrapur Beach (Orrisa) Indoor inhalation Radon Uranium Sample Radon Activity exposure Exhalation Rate concentration Name (Bqm-^) (radon)- (mBqm^h^) (ppm) effective dose (nSvy-') CHSl 1462.9 ±45.4 525.9 ±16.4 62.0 9.7 CHS2 2057.1 ±54.1 739.6 ±19.5 87.2 16.2 CHS3 2128.6 ±55.1 765.3 ±19.8 90.2 20.2 CHS4 2157.1 ±54.4 775.5 ± 19.9 91.4 20.2 CHS5 3488.6 ±70.5 1254.2 ±25.3 147.9 28.3 CHS6 2242.9 ±56.5 806.3 ± 20.3 95.1 21.8 CHS7 1514.3 ±46.5 544.4 ±16.7 64.2 9.7 CHS8 1177.1 ±40.9 423.2 ±14.7 49.9 4.9 CHS9 1400.0 ±44.7 503.3 ±16.1 59.4 13.8 CHS 10 1328.6 ±43.4 477.6 ±15.6 56.3 6.5 CHS 11 1571.4 ±47.3 564.9 ±17.0 66.6 12.1 CHS 12 1662.9 ±48.7 597.8 ±17.5 70.5 12.1 CHS 13 2428.6 ±58.8 873.1 ±21.1 103.0 24.3 CHS 14 1214.3 ±41.5 436.6 ±14.9 51.5 4.9 CHS 15 1528.6 ±46.6 549.5 ±16.8 64.8 12.1 CHS 16 1497.1 ±46.1 538.2 ±16.6 63.5 9.7 CHS 17 2074.3 ± 54.3 745.7 ±19.5 87.9 16.2 CHS 18 2628.6 ±61.2 945.0 ± 22.0 111.4 24.3 CHS 19 4551.4 ±80.6 1636.3 ±29.0 193.0 48.5 CHS20 4217.1 ±78.0 1576.1 ±29.0 185.9 40.5 Minimum 1177.1 423.2 49.9 4.9 Maximum 4551.4 1636.3 193.0 48.5 Average 21I6.6±53.7 763.9 ± 19.4 90.1 17.8 S.D 934.3 ±11.1 342.8 + 4.1 40.4 11.1 R. Std. % 44.1 ±20.6 44.9 ±21.1 44.8 62.3 200 2000 ' ' I ' ' • ' I ' ' • ' I ' • • • M ' ' ' I ' • Rsdon exhalation rate 1800 N — Linear fit 1600 I iS (0 X o c o 200'' I I I I I I ''*''''' ' i • • I I • j.^ 0 10 20 30 40 50 60 uiaiiiiTi ucN um iiction in (ppn| Figure-7. Variation of radon exhalation rate with U-concentration in the sand samples from Chhatrapur Beach (Orrisa) 201 Table -11. Track density, Radon Activity, Radon exhalation rates and Uranium concentration in bulk sand samples collected from Erasama Beach (Orrisa) Radon Exhalation Uranium Sample Radon Activity Track density Rate concentration Name (Bqm-^) (mBqm-^h-') (ppm) ERl 114.6 ±3.0 2046 ± 54 736 ±19 16.2 ER2 222.6 ± 4.2 3974 ± 75 1429 ± 27 32.4 ER3 116.3 ±3.0 2100±55 755 ±20 20.2 ER4 227.8 ±4.3 4069 ± 76 1463 ±27 36.4 ER5 228.8 ±4.4 4086 ± 79 1469 ±28 36.4 ER6 82.4 ± 2.6 1471 ±46 529 ±16 12.1 ER7 115.2 ±3.0 2057 ±54 739 ±19 16.2 ER8 243.2 ±4.4 4343 ± 79 1561 ±28 40.5 ER9 224.0 ± 4.2 4000 ± 75 1438 ±27 32.4 ERIO 246.4 ± 4.4 4400 ± 79 1582 ±28 40.5 ERll 134.4 ±3.3 2400 ± 58 863 ±21 24.3 ERl 2 256.6 ±4.5 4583 ±81 1648 ±29 40.5 ER13 256.0 ± 4.5 4571± 80 1643 ±29 40.5 ER14 136.0 ±3.3 2429 ± 59 873 ±21 24.3 ERl 5 118.4±3.1 2114±55 760 ± 20 20.2 ERl 6 114.4 ±3.0 2043 ± 54 734 ±19 16.2 ERl 7 211.2±4.1 3771 ±73 1354 ±26 28.3 ERl 8 232.0 ±4.3 4143 ±77 1489 ±28 36.4 ERl 9 123.2±3.1 2200 ± 56 791 ± 20 20.2 ER20 228.0 ±4.3 4071 ± 76 1464 ±27 32.4 ER21 120.0 ±3.1 2143 ±55 770 ± 20 20.2 ER22 225.6 ± 4.2 4029 ±76 1448 ±27 32.4 ER23 260.0 ± 4.6 4643 ±81 1669 ±29 40.5 ER24 262.4 ±4.9 4686 ±87 1685 ±31 36.4 Average: 187.5 ±3.8 3349 ±68 1204 ±24 29.0 S.D.: 6],0±0.7 1081 ± 12 391 ±4 9.2 Rel. S.D.% 32.5 ±18.4 32± 18 33 ± 17 31.7 202 Table 12. Radon exhalation rate in different building materials S.No. Sample Radon exhalation rate (m Bq m'^ h') 1. Cement 173 2. Soil 648 3. Fly ash 436 4. Unfired clay bricks 169 5. Fired clay bricks 94 6. Concrete 63 7. Marble 40 8. Mosaic 28 9. Gypsum 52 10. Limestone 13 11. Sand 108 12. Sand (present value) 1203 203 2000 I I I I I I I I I I I I I I I I I I I t Rackxi exhalation rate JC 1800 — Uneo-fit cr 1600 OQ 1400 IS 1200 c o 1 1000 (0 800 c o GOO & 400 200'' ' ' • • 1 i • '''••' M^ 0 10 20 30 40 SO 60 UbaiiiinGonoentration in (ppnf| Figure-8. Variation of radon exhalation rate with U-concentration in the sand samples from Erasama Beach (Orrisa) 204 5.3.5 Radon exhalation rate in soil and phospho-gypsum samples from Spain Soil and phospho-gypsum samples were colleted from a large industrial complex which is located in the proximities of Huelva town, south west of Spain. A large industrial wastes disposal site where two phosphate rock processing plants release their wastes is located close to Huelva town, SW of Spain. It has been partially submitted to restoration works as a preliminary step in a possible decommissioning process. Uranium concentrations are higher in these samples (Mas et al., 2006). In soil and phospho-gypsum samples "Sealed Can technique" was used for the radon exhalation measurements. All soil and phosphor-gypstim samples were grinded, dried and sieved through a 100-mesh sieve. Values of the radon activity and radon exhalation rates in soil and phosphor-gypsum samples collected from Spain are presented in Table-13. Radon activities were found to vary from 2705.7 ± 62.0 to 4454.3 ± 79.7 Bq m"^ whereas the radon exhalation rate varied from 970 ± 2.2 to 1600 ±2.8 mBq m'^ h"'. Values of indoor inhalation exposure (radon) -effective dose in these samples varies from 114.4 to 188.7 |iSv y"' in soil samples. In phospho-gypsum samples values of the radon activity activities were found to vary from 2111.4 ± 54.9 to 6254.3 ± 94.4 Bq m"^, whereas the radon exhalation rate varied from 750 ± 1.9 to 2240 ± 3.3 mBq m"^ h"'. Values of indoor inhalation exposure (radon) -effective dose in these samples varies from 88.4 to 264.1 |j.Sv y"' in phospho- gypsum samples. 205 TabIe-13 Track density, radon activity and radon exhalation rate in soil and phosphogysum samples coUeted from Spain In Soil samples < Indoor inhalation Radon exposure Description of Radon Activity Exhalation (radon)- Samples Track Density (Bqm-^) rate cffective dose (mBqm'^h') (jiSv y') 1-2-S 190.4 ±3.9 3400.0 ±69.4 1220 ±2.5 143.8 1-1-S 163.5 ±3.6 2920.0 ± 65.5 1050 ±2.3 123.8 1-8-S 151.5±3.5 2705.7 ±62.0 970 ± 2.2 114.4 1-3-S 171.8 ±3.7 3068.6 ±66.0 1100 ±2.3 129.7 1-5-S 211.8±4.1 3782.8± 73.4 1350 ±2.6 159.2 1-7-S 161.3 ±3.6 2880.0 ±55.9 1030 ±2.2 121.5 1-9-S 229.0 ± 4.3 4088.6 ± 76.0 1460 ± 2.7 172.2 1-6-S 175.0 ±3.7 3125.7 ±66.6 1120 ±2.3 132.1 1-4-S 249.4 ± 4.5 •4454.3 ±79.7 1600 ±2.8 188.7 In Phosphogysum Samples 1-1-G2 348.6 ±5.3 6225.7 ±94.0 2230 ±3.3 263.0 1-6-G2 225.0 ± 4.2 4017.1 ±75.5 1440 ±2.7 169.8 1-2-Gl 195.7 ±3.9 3494.3 ± 70.6 1250 ±2.5 147.4 1-6-Gl 190.9 ±3.9 3408.6 ±69.5 1220 ±2.4 143.9 1-3-G2 350.2 ±5.3 6254.3 ± 94.4 2240 ±3.3 264.1 1-3-Gl 226.9 ± 4.2 4051.4 ±75.8 1450 ±2.7 171.0 1-2-G2 118.2±3.1 2111.4 ±54.9 750 ±1.9 88.4 1-1-Gl 208.2 ±4.1 3717.1 ±72.9 1330 ±2.6 156.8 206 5.3.6 Radon exhalation rate in building construction materials Building materials and the soil beneath the floor are the main source of radon inside the dwellings. These are commonly derived from the natural materials which contain traces of ^^^U, "^Th and ''''K (Sorantin and Steger, 1984). A large variation in radon activity is observed in dwellings as the uranium concentrations in natural materials used as building materials vary in a wide range and from place to place. Thus it is desirable to study the radon exhalation from building materials used in different regions. The interest in the study of radon is mainly due to its detrimental effect on hiunan health. The organ that is affected most by the inhalation of radon is the lung. Studies have shown that about 5-20% of all lung cancer deaths are attributed to the inhalation of air containing radon and its progeny. Some building materials like phospho-gypsum, aerated concrete with alum shale and uranium mine tailings are known to be exceptionally radioactive. In recent years, many industrial waste materials obtained from thermal power plants, chemical and metallurgical industries are being used in building materials like bricks and cements. Materials like furnace slag, fly ash, and by-product gypsum etc contain significant amount of radio nuclides belonging to uranium and thorium series. Some houses built with fly ash mixed concrete blocks were found to show enhanced levels of radon concentration.. Use of hollow and concrete bricks has been evolved as a modem technique for fast, cheap and sturdy construction of dwellings. Composition of these bricks is different from conventional bricks which contains only mud and water. In order to evaluate the health risks due to radon inhalation it is necessary to identify and evaluate the sources of indoor radon. Due to low level of radon emanation from building materials long term measurements are required for which solid state nuclear track detectors can be used effectively and conveniently. In the present study we have made measurements for radon exhalation rate in different building materials like ceramic tiles, granite, bricks and marble etc., commonly used for building construction in this region of the state of Uttar Pradesh of India. Samples to be investigated were collected from different construction sites. Also some measurements were made for the samples from the Southwest coast of Kerala. Kerala State in India is known to have very high levels of natural background radiation owing to the rare earths rich monazite sand available in large amount. Sand 207 present in the region is an orthoplaosphate of thorium and rare earths and typically contains about 9% thorium oxide and 0.35% uranium oxide. Here exists a unique situation where a large population is being exposed to a high level radiation all through their life-span. Majority of the houses built in the Southwest coast region of Kerala are constructed with brick walls and the remaining houses have either wooden or thatched walls. 34% of the houses are made up of concrete roofs, about 38% are tiled, 12%) are thatched and remaining houses have either asbestos or galvanized iron sheet roofs. About 84% of the houses have cement flooring, 8% have tiled flooring and the remaining have bare flooring. Therefore, to study the radon emanation rates different types of bricks, cement bricks (hollow- and solid), plastered bricks, flooring materials like mosaic, Kadappa, marble, granite, ceramic tile, floor concrete, etc., were selected. At least 3 samples of each material were used for the investigation and the mean values of the results are reported. "Sealed Can Technique" was used for the radon exhalation measurements. Radon activity and radon exhalation rate measured in a number of building materials commonly used for building construction in and around Aligarh (U.P.), India are presented in Table 14. 208 Table-14. Radon activity and radon exhalation rate in Different types of building construction materials Indoor Radon inhalation Type of Radon activity exhalation rate exposure S.No (radon)-effective Materials (Bqm-^) (mBqm'^h') dose (liSvy-') 1. Ceramic Tiles (make): Face 431.7 ±20.3 267.0 ±12.5 31.4 Bel Ceramics 288.8 ±15.3 174.6 ±9.3 20.5 Liberty 453.9 ±20.8 274.4 ± 12.6 32.3 Keramos 530.1 ±23.2 320.5 ±14.0 37.7 Korel 428.5 ±19.3 259.1±11.7 30.5 Somany 523.8 ±22.5 316.6± 13.6 37.3 Romano 558.7 ±24.4 337.7± 14.8 39.8 2. Granite 2212.7 ±54.2 1337.7±32.8 157.7 3. White stone 990.4 ±28.8 598.8 ± 17.4 70.6 4. Cement block 1079.3 ±37.7 652.4 ± 22.8 76.9 5. Marble 390.4 ±19.9 236.1 ±12.1 27.8 6. Unfired brick 6885.7 ±99.2 4162.8 ±60.0 490.8 7. Fired brick 850.7 ±33.2 514.3 ±20.0 60.6 8. Plastered brick 1073.0 ±37.9 648.7 ± 22.9 76.4 Average value 1192.6 ±32.6 721.2 ± 19.8 85.0 Std.dev. 1649.5 ±21.0 997.1 ± 12.6 117.5 Rel.Std. % 138.3 ±64.4 38.2 ±63.6 138.2 209 It can be seen that there is a wide variation in radon exhalation rate of building materials. Radon activity varies from 288.8 ± 15.3 Bqm"^ to 6885.7 ± 99.2 Bqm"^ with an average value 1992.6 ± 32.6 Bqm'^; radon exhalation rate varies from 174.6 ± 9.3 mBqm' V 4162.8 ± 60.0 mBqm'V with an average value of 721.2 ± 19..8 mBqm'^h"' whereas the Indoor inhalation exposure (radon)-effective varies from 20.5 to 490.8 nSv y'^ v^th an average value of 85.0 |aSv y''( Mahur et al., 2005). The radon exhalation rate from building materials varies appreciably from one building material to another. This may due to the differences in radium content (Ramchandran and Subba Ramu, 1989) and of porosity (Folkerts et al., 1984). The results show highest radon emanation from unfired bricks while ceramic tiles give minimum value. In the case of unfired bricks, there may be many voids and the emanation can escape from inside i.e. from few cm below the surface and thus the amount of radon that can escape should depend on the intemal siuface area while in plastered brick, cement block, marble, granite and tiles the number of voids are reduced to a large extent and the radon may be emanated from the surface layer only. Radon exhalation from ceramic tiles and marble are low. The low exhalation of ceramic tiles supports the findings of O'Briren et al, 1998. Al- Jarallah, 2000, has reported high values up to 10.6 Bqm'^h"' for the granites from Saudi Arbia. Our results confirm the statement. Radon activity and radon exhalation rate measured in a number of building materials commonly used for building construction in the state of Kerala are presented in Table 15. It can be seen that there is a wide variation in radon exhalation rate of building materials. Radon activity varies from 75.0 Bqm"^ to 2212.7 Bqm"^ with an average value of 477.1 Bqm'"'; radon exhalation rate varies from 44 mBq m'^ h'' to 1337.7 mBq m''^ h'' with an average value of 286.3 mBq m"^ h"' whereas the effective dose equivalents for radon decay products vary from 5.2 to 157.7 ^iSv y'' with an average value of 33.7 |iSv y'. In the case of plastered bricks covered with sealants, radon activity varies from 220 Bqm'^ to 628 Bqm'^ with an average value of 451.3 Bqm'^, radon exhalation varies from 130 mBq m"^ h'" to 371 with an average value of 266.6 mBqm'^h"'. Radon exhalation was found to increase slightly with acrylic exterior and acrylic emulsion while it decreases with others. The results show highest radon emanation from granite while cement brick (hollow) give minimum value. Figure 9 shows the variation of uranium and radon exhalation rate for different building materials. 210 Table -15 Concentration of uranium and radon emanation in different building materials Radon U-activity emanation rate U-concentration S.N. Building material ±SD(Bqkg-») ±SD ±SD(ngg') (mBqm"^ h"') 1. Brick: Top layer of the 2.24 + 0.9 55.6 ±12 227 ±33 furnace 2. Brick: Middle layer of 2.04 ± 0.8 50.6±12 231 ±29 the furnace 3. Brick: Bottom layer of 1.95 ±0.8 48.4 ± 11 257 ±36 the furnace 4. Cement hollow brick 1.45 ±0.8 36.0 ±10 44 ± 12 5. Cement Solid brick 2.45 ±1.1 60.8 ±16 141±18 6. Plastered brick 6.95 ±2.1 172.4 ±28 308 ±58 7. Concrete 1.84 ±0.8 45.6 ±11 181±21 8. Mosaic 1.04 ±0.8 25.8 ±9 136±21 9. Kadappa 1.08 ±1.1 26.5 ± 6 30 ±9 10. Ceramic tile 1.05 ±0.9 26.0 ±5 17±7 11. Granite 1.25 ±0.9 28.0 ± 9 25 ±9 12. Marble 1.81 ±1.2 45.0 ±10 86 ± 18 211 350 -;«. ^ 300 250 100 50 5 6 7 8 Building materials • Rn emenation rate U-activity Figure-9. 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(Ed.), The Natural Radiation Environment. Wiley Eastern Limited, India, pp. 35-42 Sorantin H., and Steger, F., 1984. Natural radioactivity of building materials in Austria. Rad. Prot. Dos. 7, 59-63. Ulbak, K., Jonnassen, J and Backmark, K., 1984. Radon exhalation from samples of concrete with different porosities and fly ash additives. Radiat. Prot. Dosim. 7, pp. 45-51. UNSCEAR, 2000. Sources and effects of ionizing radiation. United Nations Scientific Committee on the Effect of Atomic Radiation, United Nations, New York Vijayan, V., Behra, S.N, 1999. Naik A (Eds.) Enviommental management in coal mining and thermal power plants. Techno science, Jaipur, pp.453-456. 215 Papers Published in Refereed Journals. 1. Concentration of indoor radon and its daughters in dwellings of Palampur City, Himachal Pradesh. R. Kumar, A.K. Mahur, A.K. Varshney and Rajendra Prasad. Indian Journal of Environmental Protection. Vol. 23 (10), (2003) 1098-1101. 2. '^''AU ion irradiated modification in CR-39 by positron aimihilation. Rajesh Kumar, A.K. Mahur, K.K. Dwivedi, D. Das and R. Prasad. Indian Journal of Physics, 78A 2 (2004) 225. 3. The distribution of indoor radon levels in dwellings of Palampur and Baijnath, Himachal Pradesh. R. Kimiar, A.K. Mahur, A.K. Varshney and Rajendra Prasad Indian Journal of Environmental Protection. Vol. 24, 8 (2004) 588-592. 4. Radon exhalation rate from different types of building construction materials through ssntd's and estimation of lung cancer risk. A. K. Mahur, Rajesh Kumar and Rajendra Prasad Environmental Geo Chemistry Journal, Vol. 8, no. 1 <& 2 (2005) 300- 305. 5. Study ofradon exhalation rate and uranium concentration from fly ash produced in the combustion of coal using SSNTD's. R. Kumar, A.K. Mahur, A. K. Singh and Rajendra Prasad. Indian Journal of Environmental Protection, 25 (7) (2005) 609-611. 6. Estimation of indoor radon levels in the dwellings along the South West Coast of Kerela. A. K. Mahur, Rajesh Kumar P.J.Jojo and Rajendra Prasad Radiation Protection and Environment Vol. 28, No. 1-4. (2005) 203- 205. 7. Radon activity and exhalation rates measurements in fly ash from a thermal power plant. R. Kumar, A. K. Mahur, D. Sengupta and Rajendra Prasad Radiation Measurements. Vol. 40, (2005) 638-641. 8. Free Volume Study of 70 MeV carbon induced modification in Polymers through positron annihilation. R. Kumar, S.A. AllA.K.Mahur, D. Das, A. H. Naqvi, H. S. Virk and R. Prasad Nucl. Instr. and Meth. in Physics Research B 244 (2005) 257-260. 9. Radon levels in dwellings of some Indian cities A. K. Mahur, R.Kumar P. J. Jojo, A. Kumar, A. K.Singh, A. K.Varshney and Rajendra Prasad. Asian Journal of Chemistry Vol. 18 No. 5 (2006) 3371-3375. 10. Study of radon exhalation rate from different types of building construction materials through SSNTD's and estimation of lung cancer risk A. K. Mahur, Rajesh Kumar, Ameer Azam, P. J. Jojo and Rajendra Prasad Journal of Chemical & Environmental Research Vol. 15 No. 3& 4 (2006) 306- 312. 11. Study of indoor radon levels in the some dwellings of Thankassery town in Kerala A. K. Mahur, Rajesh Kumar P.JJojo and Rajendra Prasad Journal of Chemical & Environmental Research Vol. 15 No. 34& 4 (2006) 287- 291. 12. An investigation on radon exhalation from fly ash produced in the combustion of coal. R. Kumar, A.K. Mahur, A. K. Singh and Rajendra Prasad. Environmental Geochemistry, Vol. 9, No. 1. (2006) 47-59. 13. Estimation of radon exhalation rate, natural radioactivity and radiation doses in fly ash samples from Durgapur thermal power plant West Bengal, India A. K. Mahur, Rajesh Kumar, D. Sengupta, Rajendra Prasad Journal of Enviommental Radioactivity Vol. 99 (2008) 1289 - 1293. 14. Measurement of natural radioactivity and radon exhalation rate from rock samples of Jaduguda Uranium Mines and its radiological implications A. K. Mahur, Rajesh Kumar, R. G. Sonkawade, D. Sengupta and Rajendra Prasad Nucl. Instr. and Meth. in Physics Research B 266 (2008) 1591-1597 15. An investigation of radon exhalation rate and estimation of radiation doses in coal and fly ash samples A. K. Mahur, Rajesh Kumar, Meena Mishra, D. Sengupta and Rajendra Prasad Applied Radiation and Isotope Vol. 66 (2008) 401-406. 16. Measurment of effective radium content of sand samples collected from Chhatarpur Beach, Orissa, India using track tech technique. A. K. Mahur, M.Shakir Khan, A.H. Naqvi and Rajendra Prasad and A. Azam, Radiation Measurements Vol. 43 (2008) S520-S522. 17. Radon exhalation rate from sand samples the newly discovered high background radiation area at Erasama beach placer deposit of Orissa, India R. Kumar, A. K. Mahur, Sulekha Rao, D. Sengupta and Rajendra Prasad Radiation Measurements Vol. 43 (2008) SS08-S511. 18. Study of optical band gap and carbonaceous clusters in swift heavy ion irradiated polymers with UV-Vis spectroscopy R. Kumar, S. Asad Ali, A.K. Mahur, H.S. Virk, F. Singh, S.A. Khan, D.K. Awasthi, R. Prasad Nucl. Instr. and Meth. in Physics Research B 266 (2008) 1788-1792. 19. Indoor radon monitoring in some buildings surrounding the national Hydroelectric Power Corporation (NHPC) project at Upper Siang in Arunachal Pradesh, India A. K. Mahur, Rajesh Kumar, Meena Mishra, Ameer Azam and Rajendra Prasad. Indian Journal of Physics, 2008 (In Press) 20. Radon exhalation rate in Chhatarpur beach sand samples of high background radiation area and estimation of its radiological implications A. K. Mahur, Rajesh Kumar, D. Sengupta and Rajendra Prasad Indian Journal of Physics, 2008 (In Press) 21. Measurement of indoor radon, thoron and their progeny in some Indian dwellings of U. P., India using twin chamber dosimeter cups with SSNTDs A. K. Mahur, Rajesh Kumar, R. G. Sonkawade, Ameer Azam and R. Prasad Radiation Measurements (communicated). Papers Presented/ Accepted in National/ International Conferences/Workshops. 22. Indoor radon levels in dwellings of Palampur, Himachal Pradesh. R. Kumar, A. K. Mahur, A. K. Varshaney and Rajendra Prasad 21** International Conference on Nuclear Tracks in Solides, 2002, New Delhi. 23. Study of ion induced modification in Makrofol-KG polycarbonate by positron annihilation lifetime measurements. R. Kumar, A.K, Mahur, D. Das and Rajendra Prasad Them Symposium on Novel Polymeric Materials, BARC, Mumbai, India, 2003. 24. '^^Au ion irradiated modification in CR-39 by positron annihilation. R. Kimiar, A.K. Mahur, K.K. Dwivedi, D. Das and Rajendra Prasad National Seminar on Science and Technology of Nanomaterials, CGCRI, Kolkata, India, 2003. 25. The study of radon exhalation from fly ash produced from coal combustion. R. Kumar, A.K. Mahur, A.K. Singh and Rajendra Prasad National Conference on Environmental Pollution, Prevention and control. Organized by University Polytechniqe, A.M.U., Aligarh. 2003. 26. Positron annihilation lifetime studies of irradiated CR-39 (DOP) Polycarbonate. R. Kumar, A.K. Mahur and Rajendra Prasad 13"* International Conference on Positron Annihilation (ICPA-13) Kyoto, Japan, 2003. 27. C5+ ion induced modification in Makrofol-N polycarbonate by positron annihilation lifetime studies. R. Kumar, A.K. Mahur. D. Das and Rajendra Prasad Condensed Matter days-2003, Symposiirai on Condensed Matter Physics, Department of Physics, Jadavpur University, Kolkata. 28. An investigation of radon exhalation from fly ash produced in the combustion of coal. R. Kumar, A.K. Mahur, A.K. Singh and Rajendra Prasad. 13*National symposium on Solid State Nuclear Track Detectors (SSNTD's) at Department of Physics, Osmania University, Hyderabad, dviring, October 16-18, 2003. 29. Study of ^^^Rn levels in some dwellings around Nuclear Atomic Power Station. R. Kumar, A. K. Mahur and Rajendra Prasad. 13*^ National symposium on Solid State Nuclear Track Detectors (SSNTD's) at Department of Physics, Osmania University, Hyderabad, during, October 16-18, 2003. 30. The indoor concentration of indoor radon and its daughters in dwellings of Palampur city, Himachal Pradesh R. Kumar, A. K. Mahur, A. K. Varshney and rajendra Prasad. 91^' hidian Science Congress at Department of Physics, Chandigarh, 2004. 31. Estimation of radon exhalation rate in rock samples fromJadugud a uranium mine using SSNTD technique. A. K. Mahur, Rajesh Kumar, D. Sengupta and Rajendra Prasad 14^ International Conference on Solid State Dosimetry, Yale University, New Haven, CT, USA, during, June 27 - July 2, 2004.(Accepted). 32. Radon activity and exhalation rates measurements in fly ash from a thermal power plant. R. Kumar, A. K. Mahur, D. Sengupta and Rajendra Prasad 22""* International Conference on Nuclear Tracks in Solids, Barcelona, 23-27, August 2004. 33. Radon exhalation rate in rock samples fromJadugud a urani\rai mine using Nuclear Track Detector. A. K. Mahur. Rajesh Kumar, D. Sengupta and Rajendra Prasad Workshop on " Accelerator and Enviromnental Radiation Safety" to be held on 22- 23 April, 2004, at Nuclear Science Centre, New Delhi. 34. Effect of soil as additive in the radon exhalation rate fromfl y ash R. Kumar, A. K. Mahur and Rajendra Prasad Workshop on " Accelerator and Environmental Radiation Safety" to be held on 22- 23 April, 2004, at Nuclear Science Centre, New Delhi. 35. Radon activity and radon exhalation studies in hidian fly ash samples from thermal power plant A. K. Mahur, Rajesh Kumar, D. Sengupta and Rajendra Prasad National Conference cum Workshop on Solid State Nuclear Track Detectors and Applications, during 1-3 November, 2004. at DAV College, Amritsar (Presented as an oral Presentation). 36. The distribution of indoor radon levels in dwellings of Palampur and Baijnath, Himachal Pradesh. R. Kimiar, A.K. Mahur, A.K. Varshney and Rajendra Prasad Recent advances in Himalayan Geology with special reference to the NW Himalaya, during 6-8 October, 2004.(Presented as an oral Presented). 37. Free volume study of SHI induced modification in Polyamide Nylon-6 polymer. R. Kumar, S. A. Ali, A. K. Mahur D. Das, A. H. Naqvi, H. S. Virk and R. Prasad hido German Workshop on Synthesis and Modification of Nano- structured Materials by Energetic Ion Beams at Nuclear Science Centre, New Delhi, hidia, during 20-25, 2005. 38. Study of Radon and its Daughters in Dwellings of Bhatinda near Thermal Power Plant R. Kiraiar, A.K. Mahur, S.A.Ali, A. Kumar, and Rajendra Prasad NUCAR 2005 Guru Nanak Dev University Amritsar- 143 005, hidia during March 15-18,2005. 39. Estimation of uranium, thorium, potassium in flyas h samples and total gamma dose emitted from the ash pond A. K. Mahur. Rajesh Kumar, D. Sengupta and Rajendra Prasad NUCAR 2005 Guru Nanak Dev University Amritsar-143 005, India during March 5- 18, 2005. 40. Radon exhalation rate fromdifferen t types of building construction materials through SSNTD's and estimation of lung cancer risk Ajay Kumar Mahur, Rajesh Kumar and Rajendra Prasad 14* National Symposium on Environment at Department of Physics, Osmania University Hyderabad, during, 5-7, 2005. 41. Estimation of indoor radon levels in the dwellings along the South West Coast of Kerela. A. K. Mahur, Rajesh Kumar P.J.Jojo and Rajendra Prasad 27* lARP Nation Conference on occupational and Environmental Radiation Protection Bhabha Atomic Research Centre (BARC) Mubmai, 23-25.Nov., 2005. 42. Study of radon activity and radon exhalation rate in sand samples from Erasama Beach Placer Deposit, Orissa R. Kumar, A. K. Mahur, D. Sengupta and Rajendra Prasad 14* National Symposium on Solid State Nuclear Track Detectors (SSNTD's) at Department of Applied Physics, Aligarh MuslimUniversity,Aligarh, during, Nov. 10-12,2005. 43. Measurement of radon exhalation rates in soil samples collected from some areas of Jharkhand state R. Kumar, A. K. Mahur, R. G. Sonkawade, V. N. Bhardwaj, B. S. Pandit B. P. Singh and Rajendra Prasad 44. Study of indoor radon levels in the some dwellings of Thankassery Kerala A. K. Mahur, Rajesh Kumar, P. J. Jojo and Rajendra Prasad 14* National Symposium on Solid State Nuclear Track Detectors (SSNTD's) at Department of Applied Physics, Aligarh Muslim University, Aligarh, during, Nov. 10-12,2005. 45. Study of radon exhalation rate from different types of building construction materials through SSNTD's and estimation of lung cancer risk. A. K. Mahur, Rajesh Kumar, P. J. Jojo and Rajendra Prasad 14th National Symposium on Solid State Nuclear Track Detectors (SSNTD's) at Department of Applied Physics, Aligarh MuslimUniversity, Aligarh, during, Nov. 10-12,2005. 46. Si Ion Induced Modification in Makrofol-KG Polycarbonate R. Kumar, S. A. Ali, A. K. Mahur, S. A. Khan, D. K. Avasthi and R. Prasad 50th (Golden Jubilee) Department of Atomic Energy Solid State Physics Symposium at Bhabha Atomic Research Centre (BARC) Mubmai, 5-9, 2005. 47. Radon levels in dwellings of some Indian cities A. K. Mahur, R.Kumar P. J. Jojo, A. Kumar, A. K.Singh, A. K.Varshney and Rajendra Prasad. National Conference on Lasers, Smart Materials & Radiation Physics, at Department of Physics Sant Longowal Institute of Engineering and Technology longowal, Sangrur (Punjab) during 17-18 March, 2006. 48. Indoor radon/thoron measurements in some Indian dwellings of U.P., India using twin chamber dosimeter cups. A. K. Mahur, Rajesh Kumar, Ameer Azam, R. G. Sonkawade and Rajendra Prasad 23^** International Conference on Nuclear Tracks in Solids,Beijing (China), 11-15 September 2006. 49. Natural radioactivity and radon exhalation studies in Indian fly ash samples from thermal power plants. A. K. Mahur, Rajesh Kumar, D. Sengupta and Rajendra Prasad ly^ International Conference on Nuclear Tracks in Solids, Beijing (China), 11-15 September 2006. (Presented). 50. Radon exhalation rate and natural radioactivity in the newly discovered high background radiation area at Erasama Beach Placer Deposit of Orissa, India R. Kumar, A. K. Mahur, Sulekha Rao, D. Sengupta and Rajendra Prasad 23^** International Conference on Nuclear Tracks in Solids, Beijing (China), 11-15 September 2006. (Presented). 51. Measurment of effective radium content of sand samples collected from Chhatarpur Beach, Orissa, India using track etch technique. A. K. Mahur, M.Shakir Khan, A.H. Naqvi and Rajendra Prasad and Ameer Azam 23''* hitemational Conference on Nuclear Tracks in Solids, Beijmg (China), 11-15 September 2006. (Presented) 52. Indoor radon levels in some dwellings of Gujarat and Jharkhand State India A. K. Mahur, R. Kumar, N. L. Singh, V. N. Bhardwaj, B. Pandit, B. P. Smgh, and R. Prasad. 10* International Symposium on Radiation Physics (ISRP-10) Coimbra, Portugal. 53. Measurement of radon exhalation rate and estimation of radiation doses in coal and fly ash samples from a thermal power plant A, K. Mahur, Meena Mishra, Rajesh Kumar, D. Sengupta and R. Prasad 8* Nuclear and Radiochemistry Symposium Feb, 14-17,2007. The Maharaja Sayajirao University of Baroda Vadodra. 54. Radon exhalation rate in coal and fly ash from thermal power plants, enviroimiental implications. Ajav Kumar Mahur, Meena Mishra, Rajesh Kumar and Rajendra Prasad Fifteenth National Symposixim on Environment (NSE-15) June 5-7,2007. Department of Physics Bharathiar University, Coimbatore, India. 55. Natural radionuclides and radon exhalation study in soil samples from some areas of Jharidiand A. K. Mahur. Rajesh Kumar, R. G. Sonkwade, V. N. Bhardwaj, B. Pandit, B. P. Singh and Rajendra Prasad Conference on Accelerator and low level Radiation safety April 26-2, 2008 at Inter University Accelerator Cenfre New Delhi. 56. Study of indoor radon/thoron in some dwellings surrounding Narora Atomic Power Station (NAPS) using twin chamber dosimeter cups A. K. Mahur, Rajesh Kumar, R. G. Sonkawade, Ameer Azam and Rajendra Prasad Conference on accelerator and low level radiation safety, April 26-27,2007 at Inter University Accelerator Centre New Delhi. 57. Radon exhalation rate in Chhatarpur beach sand samples of high background radiation area and estimation of its radiological implications A. K. Mahur, Rajesh Kumar, D. Sengupta and Rajendra Prasad Fifteenth national symposium on Solid State Nuclear Track Detectors and their Applications (SSNTD-15) Department of Physics, during June 21-23, 2007 H. N. B. Garhwal University Badshahi Thaul CampusTehri Garhwal Uttarkhand. 58. Indoor radon monitoring in some dwelling surrounding the National Hydroelectric Power Corporation (NHPC) Project at Upper Siang in Arunachal Pradesh, India A. K. Mahur, Rajesh Kumar, Meena Mishra and Rajendra Prasad Fifteenth national symposium sn SoUd State Nuclear Track Detectors and their applications (SSNTD-15) Department of Physics, during June 21-23, 2007 H. N.B. Garhwal UniversityBadshahi Thaul CampusTehri Garhwal Uttarkhand. 59. Measurement of natural radioactivity and radon exhalation rate from rock samples of Jaduguda Uranium Mines and its radiological implications A. K. Mahur, Rajesh Kumar, R. G. Sonkawade, D. Sengupta and Rajendra Prasad 18"^ International Conference on Ion Beam Analysis, during 23-28 September 2007. University of Hyderbad, Central University P.O Hyderabad A.P, India. 60. Study of optical band gap and carbonaceous clusters in swift heavy ion irradiated polymers with UV-Vis spectroscopy R. Kumar, S. A.AU, A.K. Mahur. H.S. Virk, F. Singh, S.A. Khan, D.K. Awasthi, R. Prasad 18"' Intemational Conference on Ion Beam Analysis, during 23''*-28* September 2007. University of Hyderbad, Central University P.O Hyderabad A.P, India. 61. Indoor radon monitoring and effective dose measurement in some dwellings of Gujarat and Jharkhand states of India A. K. Mahur, R. Kumar, N. L. Singh, V. N. Bhardwaj, B. Pandit B. P. Singh and R. Prasad Intemational Conference on Radioecology and Environmental radioactivity at Bergen, Norway during 16-20 Jime, 2008. 62. Assessment of natural radioactivity in soil collected from Jaduguda U-mines area East Singhbhum shear zone, Jharkhand India and radiological implications A. K. Mahur, R.Kumar, M. Mishra, S. A. Ali, R. G. Sonkawade, B. P. Singh, V. N. Bhardwaj and Rajendra Prasad International Conference on Radioecology and Environmental radioactivity at Bergen, Norway during 16-20 June 2008 63. Radon exhalation, radioactivity and radiation risk in building construction materials from aroimd Jaduguda Uranium mines, India A. K. Mahur, M. Maharana, Rajesh Kumar, D. Sengupta, R. Rengarajanc, R. Prasad 24h* International Conference on Nuclear Tracks in Solids, Physics Department of the University of Bologna Italy during 1-5, September 2008. (Presented) 64. Study of indoor radon, thoron and progeny in some dwellings near fertilizer plant and Atomic Power Station using twin chamber dosimeter cups with SSNTDs A. K. Mahur, Rajesh Kumar, R. G. Sonkawade, Ameer Azama and Rajendra Prasad 24* International Conference on Nuclear Tracks in Solids, Physics Department of the University of Bologna Italy during 1-5, September 2008. (Presented) 65. Investigations of radon exhalation rates, natural radioactivity and radiation exposure in fly ash fromtherma l power plants, India 24 International Conference on Nuclear Tracks in Solids, Physics Department of the University of Bologna Italy during 1-5, September 2008. (Presented) A. K. Mahur, Rajesh Kumar, Meena Mishra, D. Sengupta and Rajendra Prasad 24hth International Conference on Nuclear Tracks in Solids, Physics Department of the University of Bologna Italy during 1-5, September 2008. (Presented) 66. Radon exhalation and radiation exposure from Indian commercial granites M. Mishra, A. K. Mahur and Rajendra Prasad 24' International Conference on Nuclear Tracks in Solids, Physics Department of the University of Bologna Italy during 1-5, September 2008. (Presented) Journal of Environmental Radioactivity 99 (2008) 1289-1293 Contents lists available at ScIenceDirect Journal of Environmetttai Radioactivity ELSEVIER journal homepage: www.elsevier.com/locate/teftvrad Estimation of radon exhalation rate, natural radioactivity and radiation doses in fly ash samples from Durgapur thermal power plant, West Bengal, India A.K. Mahur^*, Rajesh Kumar^, D. Sengupta''. Rajendra Prasad* ' Department of Applied Physics. ZH. College of Engineering and Technology. Aligarh Muslim University. Aligarh 202002. India ''Department o/Geology and Geophysics, l.l.T. Kharagpur, Kharagpur 721302, India ARTICLE INFO ABSTRACT Article histoiy; Coal and its by products often contain significant amounts of radionuclides, including uranium which is Received 27 October 2007 the ultimate source of the radioactive gas radon. Burning of coal and the subsequent emission to the Received in revised forin 25 January 2008 atmosphere cause the re-distribution of toxic trace elements in the environment. Due to considerable Accepted 18 March 2008 economic and environmental importance and diverse uses, the collected fly ash has become a subject of Available online 7 May 2008 worldwide interest in recent years. In the present study, radon exhalation rate and the activity con centration of ^'*U, ^'^Th and '^K radionuclides in fly ash samples from Durgapur thermal power plant Keywords: (WB) have been measured by "Sealed Can technique" using LR-115 type II detectors and a low level Nal Riidon exhalation rate (Tl) based gamma ray spectrometer, respectively. Radon exhalation rate varied from 360.0 to EfTective dose Gamma ray spectroscopy 470.0 mBq m~^ h"' with an average value of 406.8 mBq m"^ h~'. Activity concentrations of ^^U ranged Radium equivalent activity from 84.8 to 126.4 Bq kg' with an average value of 99.3 Bq kg"', ^^^Th ranged from 98.1 to 140.5 Bq kg"' LR-115 type II detector with an average value of 112.9 Bq kg"' and *K ranged from 267.1 to 364.9 Bq kg"' with an average value of 308.9 Bq kg"'. Radium equivalent activity obtained from activity concentrations is found to vary from 256.5 to 352.8 Bq kg"' with an average value of 282.5 Bq kg"'. Absorbed gamma dose rates due to the presence of ^'*U, ^^^Th and ^K in fly ash samples vary in the range 115.3-158.5 nCy h"' with an average value of 126.4 nCy h"'. While the external annual effective dose rate varies from 0.14 to 0.19 mSvy"' with an average value of O.lSmSvy"', effective dose equivalent estimated from exhalation rate varies from 42.5 to 55.2 jiSvy"' with an average value of 47.8 jiSvy"'. Values of external hazard index Hex for the fly ash samples studied in this work range from 0.69 to 0.96 with a mean value of 0.77. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction Oojo et al., 1993a,b), fly ash has been found to contain enhanced levels of uranium as compared to coal. Apart from inhalation, an Fly ash, being used frequently as building construction material additional radiation hazard can be the solids fall out, resulting in is an incombustible residue formed from 90% of inorganic matter in elevated concentration of natural radionuclides in the surface soils coal and escapes (0.5-2%) into atmosphere and biosphere (Papas- around the power plants (Bem et al., 2002). Due to considerable tefanou and Charalanbous, 1979). Coal based thermal power plants economic and environmental importance, the collected fly ash has contribute about 72% of the power generation in India. Indian coal become a subject of worldwide interest in recent years because of is of bituminous type, having high ash content with 55-60% ash and its diverse uses in manufacture of cement, clay ash bricks, ash it has been estimated that ~ 100 million tons of fly ash is produced bricks/blocks, cellular concrete blocks, asbestos products, in re per annum (Prasad et al., 1990; Vijayan and Behra. 1999; Baba, placement of sand and cement in building materials, for filling of 2002). Coal like other materials found in nature contains radionu underground cavities, in construction of roads/rail embankments/ clides like uranium, thorium and potassium. Combustion of coal reinforced earth walls, mine filling and in agriculture, etc. Radon enhances the natural radiation in the vicinity of the thermal power exhalation rate is of prime importance for the estimation of radi plant through the release of the radionuclides and their daughters ation risk from various solid waste materials. The radon exhaling in the surrounding ecosystem. Owing to its small size and hence properties of porous materials, both naturally occurring - like soil, large surface area, the ash has a greater tendency to absorb trace coal and rocks and man-made - like mining wastes, fly ash and elements that are transferred from coal to waste products during many building materials, etc., have been the subject of several combustion (Culec et al., 2001). In our previous measurements investigations Qonassen, 1983; Karmadoost et al., 1988; Kumar et al., 1999,2005). Earlier studies (Mishra and Ramchandran, 1991) • Corresponding author, Tel.: +91 571 2742837. +91 9412808481 (mobile). on coal and fly ash have shown that Indian coals contained 1.8- E-mail address: [email protected] (A.K. Mahur). 6.0 ppm ^^*U and 6.0-15.0 ppm of ^^^Th. But recent studies have 0265-931 X/$ - see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2008.03.010 1290 A K Mahur et at /Journal of Environmental Radioactivity 99 (2008) 1289-1293 indicated as high as 50 ppm ^^^Th and 10 ppm of ^^*U in the pond 1997; MacKenzie. 2000; UNSCEAR. 1993, 2000). The results for the ash generated from coal combustion (Mandal and Sengupta, 2003). values of the radon activity and radon exhalation rates from the fly Radioactive properties of fly ash are of importance as some con ash samples are presented in Table 1. Radon activities were found to struction materials might raise the concentration of airborne vary from 1005.1 ±29.1 to 13083 ± 43.3 Bq m"^ with an average radioactivity in indoor air to unacceptable levels, especially in value of 1132.9 ±39.1 Bqm"^, whereas the radon exhalation rate places having low ventilation rates (Rawat et al., 1991; Khan et al., varied from 360 ± 10.4 to 470 ± 15.5 mBq m"^ h"' with an average 1992). In the present study, radon exhalation rates have been value of 406.8 ± 14.0 mBq m"^ h"'. Radon activity and radon exha measured m fly ash samples from Durgapur thermal power plant lation rates are higher than our previous measurements on fly ash situated in the state of West Bengal in India. The analysis of samples from different thermal power stations situated in two dif radioactivity has been carried out for ^^*U. ^^^Th and """K estimation ferent states of the countiy (Table 2). by a low level Nal (Tl) gamma ray spectrometer. Absorbed radiation The activity concentrations of ^^'U and ^^^Th and ''°K together doses and radiation risk have been estimated. with their average values in fly ash samples are given in Table 3. The activity concentrations of ^^*U and ^^^Th vary from 84.8 ± 0.9 to 2. Materials and methods 126.4 ± 1.3 Bq kg~' with an average value of 99.3 ± 1.3 Bq kg~' and 21 Radon exhalonon rate from 98.1 ±0.2 to 140.5 ± 0.3 Bq kg"' with a mean value of 112.9 ± 0.3 Bq kg"', respectively. The activity concentrations of Radon exhalation rate is of prime importance for the estimation of radiation risk ^^^Th are higher than those of ^^*U. In previous studies (Mandal and from various matenals "Sealed Can technique" was used for the radon exhalation Sengupta, 2003), it has been observed that the activity concentra measurements In such measurements, it is expected that the exhalation rate de tions of ^^^Th are much higher than those of ^^^U in feed coal pends upon the matenal and its amount as well as on the geometry and dimension of the Can Collected fly ash samples from the Durgapur thermal power plant in West samples in Kolaghat thermal power station (WB) and combustion Bengal, India were dried and sieved through a 100-mesh sieve They were placed in of coal enhances the radioactivity in fly ash (Jojo et al., 1993a) '"'K in the Cans (diameter 70 cm and height 75 cm) similar to those used in previous ashes ranges from 267.1 ±2 5 to 364.9 ± Bq kg"' with an average calibration experiment (Singh et al, 1997) In each Can, a LR-115 type II plastic track value of 308.9 ± 2.4 Bq kg"'. Activity concentration of radionuclides detector (2 cm x 2 cm) was fixed at the top inside of the Can Thus the sensitive lower surface of the detector is freely exposed to the emergent radon so that it is IS high as compared to those in fly ash from the thermal power capable of recording the alpha particles resulting from the decay of radon in the Can station situated in other parts of India (Mandal and Sengupta, 2005; Radon and its daughters reach an equilibrium concentration after 4 h and thus the Kumar et al., 1999), e g. in Uttar Pradesh (Kumar et al., 1999) where equilibrium activity of emergent radon could be obtained from the geometry of the the activity concentration of ^^^Ra (daughter product of ^^^U) is Can and the time of exposure After the exposure for 100 days, the detectors from all found to be 39.0 Bq kg"' and of ^^^Th is 40.0 Bq kg"' but is the Cans were retrieved The detectors were etched in 2 5 N NaOH at 60 "C for a period of 90 mm in a constant temperature water bath for revelation of tracks comparable with those from Kolaghat thermal power station Resulting alpha tracks on the exposed face of the detector foils were scanned under (Mandal and Sengupta, 2005) situated in the same state West an optical microscope at a magnification of 400x From the track density, the radon Bengal of India. It has been reported (Mandal and Sengupta, 2005) activity was obtained using the calibration factor of 0056Trcm"^d"'(Bqm"')"' that the concentration of radionuclide ^^*U in the ash samples from obtained from an earlier calibration experiment (Singh et al, 1997) Following ex pression gives the exhalation rate (Khan et al, 1992, Fleischer and Morgo-campero, KTPS IS much higher than those in the ash samples of other thermal 1978, Kumar et al, 2005) power stations in operation in different states of India. Ash samples from Durgapur thermal power plant as studied above contain CV/ Ex = •A[T + (l/A){e-"--i}] (1) a significant amount of radionuclides and also higher radon exhalation rates. Thus, the higher exhalation rates may be related to where Ex - radon exhalation rate (Bqm"^h"'). C - integrated radon exposure as higher ^•'*U concentration. Fig. 1 shows the variation of radon measured by LR-115 type II plastic track detector (Bq m"^ h), V - effective volume of exhalation rate with ^^'U activity concentration There seems to be the Can (m^), A - decay constant for radon (h"'), T - exposure time (h), A - area covered by the Can (m^) positive correlation between them. It is worth mentioning that it is difficult to predict the radon exhalation rate from the concentration 2^ Radiometric analysis of uranium or its decay series products in a sample, since the radon exhalation rate depends also on the texture and grain size All collected fly ash samples were stored in polyethylene bags They were dried composition. To establish the correlation between ^^*U and ^'^Th for 24 h in an air-circulation oven at 110 °C About 250 g of each sample was packed in plastic conUiners and sealed for four weeks (El-Arabi, 2005) for ^''U and ^'^Th to activity concentration and ^'^Th and ^°K activity concentrations in attain secular equilibrium with their decay products and to prevent '^^Rn and '^"Rn the fly ash samples of the present study, the plots are shown in Figs. loss A low level gamma ray spectrometric set up at National Geophysical Research 2 and 3. A week correlation exists between different quantities Institute, Hyderabad, was used for the estimation of'^U, ^'^Th and *'K The detector consisted of a 5" x 6" Nal (Tl) crystal coupled to a 5" diameter photomultiplier tube A 256-channel data set covering 0-3 MeV is obtained through a multi-channel analyzer (MCA) card (on a computer) that provided a gam-stabilized spectrum ^^'U Table 1 and ^'^Th were assessed from the intensity of the gamma ray peaks of their Track density, radon activity and radon exhalation rate in fly ash samples from daughters ^"BI (176 MeV) and ^""TI (2 62 MeV), assuming all daughter products to Durgapur thermal power plant (WB) be in equilibrium whereas *'K was measured directly from its own gamma ray of 1.46 MeV The samples were analyzed for a very long counting time (generally 7- Sample Track density Radon activity Radon exhalation 12 ks) The standard samples with which the set-up needs to be calibrated are (1) (Cm-'d-') (Bqm-3) rate (mBq m-^h~') containing thonum with a little uranium, (2) containing only uranium and (3) irr-Di 62.1 ±2.2 1109.1 ±39.7 399±143 containing only potassium In the present laboratory set up, the standard samples irr-D2 63.7 ±2.2 1138.3 ±40 3 409±145 were prepared using powders obtained from the US Atomic Energy Commission, irr-D3 596±21 1064.2 ±38 9 382 ±13 9 New Brunswick Laboratory Assaying was earned out by the method followed at the irr-D4 731 ±2.4 13049±432 468 ±15 5 National Geophysical Research Institute, Hyderatud The details of the method of irr-D5 61.3 ±2.2 1094.3 ±39.5 394±14 2 assaying are given elsewhere (Rao, 1974, Mandal and Sengupta, 2003,2005) irr-D6 73.3 ±2.4 1308.3 ±43.3 470 ±15.5 irr-D7 56.2 ± 16 1005.1 ±291 360±104 3. Results and discussion irr-D8 e82±23 1218 4 ±41.7 438 ±14 9 irr-D9 603 ±2.1 1076 6 ±39.2 386 ±141 1010.3 ±35 6 362 ±12.7 Study of radon exhalation and natural radioactivity is of consid irr-Dio 56.6±19 erable interest with respect to investigations of ongin and distribu Average value 63.4 ±2.1 1132.9 ±391 406.8 ± 14 tion of radionuclides, radiation exposure, processing of radioactive SD 5 9±0.2 104.4 ±3.9 37.7 ± 1.4 9.2 ±93 93 ± 10.0 materials and also in radiological research (Eisenbud and Cesell, Rel. SD% 9.2 ±95 AX Mahur et at. /Journal of Environmental Radioactivity 99 (2008) 1289-1293 1291 Table 2 1000 •^r -T—r—T- -|—1—I—I—I—|—r—T ! ' 1 ' Average radon exhalation rate in ny ash samples from different thermal power plants in India • Radon exhalation rate Name of thermal power plant Average radon exhalation race • - Linear fit • (±SD)(mBqm*'h-') ^ 8001- • KasimpurAttearti(UP) 275.3 ±45.7 E PaiidihdtJhaiid(Ui>) 257.6 ±48.7 ; Obra.MiicN'Ui'CUP) 239.9±24.8 ~ 600 Kola^t^WB) 436.2 ±50.9 Durgapur (WBX present study 406.8*37.7 I Health risks are especially high in the area downward of the ~ "• - • • •* *— power plant. Being very minute, fly ash particles may tend to remain airborne for long periods leading to serious health problems O as the airborne ash can enter the lungs through inhalation and may stick to lung tissues. Due to higher radon emanating power, the 1 lung tissues may be irradiated with a-particles from radon progeny • to a high degree, increasing the possibility of lung cancer. These 1 1 1 1 1 1 1 1 1 1 1 1 1 1 • 1. radionuclides in the fly ash may migrate from the waste disposal so 90 100 110 120 130 140 site to the underlying ground water body and may also accumulate Uranium Concentration (Bq kg') in the top soil giving sufflcient chances for the radionuclides to become enriched in soil. Fig. 1. Radon exhalation rate versus uranium concentration in fly ash samples. In recent years, fly ash has been used as a replacement of sand and cement in pre-mixed concrete, manufacture of blended flyas h 3.2. Absorbed gamma dose rate measurement (D) Portland cement, aerated concrete, fly ash clay bricks and blocks and for fliling for underground cavities, etc. Thus, it is quite An attempt has been made to evaluate the total gamma dose important to estimate the radiation risk to the population from the emitted from the ash pond. The absorbed gamma dose rates (D) in radioactivity of flyash . air at 1 m above the ground surface for the uniform distribution of radionuclides (^^^Th, ^^*U and ''°K) are calculated on the basis of 3.7. Radium equivalent activity (Raeq) guidelines given by UNSCEAR (2000). The dose conversion factors for converting the activity concentrations of ^^*U, ^^^Th and ^°K into Exposure to radiation is defined in terms of radium equivalent doses (nCyh"' per Bqkg"') are 0.462, 0.604 and 0.0417, re activity (Raeq) in Bq kg~^ to compare the specific activity of mate spectively. Thus rials containing different amounts of ^^*U (^^^Ra), ^^^Th and '"K. It is calculated through the following expression (Yu et al., 1992; D = (0.462Au + 0.604A-n, + 0.0417/\K) nCy h" (3) Hayambu et al., 1995): The mean dose rate as computed from the above equation is Raeq = Ai] + 1.43/lTh + QQ7AK (2) found to be 128.84 nCyh""' which is about 2.5 times higher than the world average (51 nCy h"') as reported by UNSCEAR (2000). where Aj, Am and /\K are the activity concentrations of ^^*U. ^^^Th To estimate the annual effective dose rate, £, the conversion and ''"K in Bq kg"', respectively. In the above equation for defining coefficient from absorbed dose in air to effective dose (0.7 SvGy~') Raeq activity, it has been assumed that the same gamma dose rate is and outdoor occupancy factor (0.2) proposed by UNSCEAR (2000) produced by 370Bqkg-' of "*U or 259Bqkg-' of ^^^Th or 4810 Bq kg"' of **K. There are variations in the radium equivalent 250 T—I—I—I—I—I—I—I—I—I—I—I—]—I—I—I—I—I—I—I—I—I—I—r—I—T I—I—I—I—I—I—I—p activities of different materials and also within the same type of materials. The results may be important from the point of view of selecting suitable materials for use in building construction. • ^^U Concentration 200 Linear fit Table 3 a Activity concentrations of ^^'U, ^"Th and ^K in fly ash samples from Durgapur or thermal power plant (West Bengal, India) CO 150 Deiaib a»U *»rh *>K i^iamiries (Bq*g~') (B«ll«-') (Bqkg-') itr-bii ' 95.8*1.1 109.1 *0J! 300.7 ±2.1 IIT-D2 92.4* 1.1 1053 ±Qa 28ai±Z5 ltr-D3 95.7 ±1.1 1093 ±0.2 290.4 ±Z5 trr-b4 934 ±1.8 101.0±03 267.1 ±25 84,8±03 t inr-i» 107.6 ±0a 272.4 ±Z1 irr-D6 95.7±1J 98.1 ±0.2 354.7 ±Z5 3 114S±13 136.9 ±03 344.5 ±Z5 irr-07 50 irr.D8 94S±W 103.8 ±02 287.8 ±2.1 /rr-D9 126.4 ±U 140.5 ±03 364.9±Z5 irr-010 98.8±Z3 117.6 ±05 32&4±25 No.of$am|rtes 10 10 10 J_ _L Max. 1M.4±13 14O.S±03 364,9 ±25 90 100 110 120 130 140 150 Mln. 84JI±1JO 98.1 ±0.2 267.1 ±25 Average 993 ±13 112.9 ±03 3085±Z4 "*Th Concentration (Bq kg') SD 1«±0.4 13.8 ±0.1 34.0 ±a2 Fig. 2, Variation of ^"U activity concentration versus ^'^Th activity m fly ash samples. 1292 A.K. Mahur et at /Journal of Environmental Radioactivity 99 (2008) 1289-1293 600 T—I—I—I—I—I—I—I—I—I—r- I I I—r I I I I I I I—r I I—r In these calculations, the maximum radon concentration from the building material was assessed by assuming the room as 0 % Concentration a cavity with S/V= 2.0 m~' and an air exchange rate of 0.5 h"'. The annual exposure to potential alpha energy £p (effective dose Linear fit 500 equivalent) is then related to the average radon concentration CRH by the following expression: 8760 x n X f X CiR n Ep |WLMy- (8) 170x3700 where, CRR is in Bq m~^: n, the fraction of time spent indoors taken as 0.8; 8760, the number of hours per year; 170, the number of hours per working month and F is the equilibrium factor for radon. Radon progeny equilibrium is the most important quantity when dose calculations are to be made on the basis of the measurement of radon concentration. Equilibrium factor F quantifies the state of equilibrium between radon and its daughters and may have values 200 - 0 < F< 1. The value of F is taken as 0.4 as suggested by UNSCEAR (2000). From radon exposure, the effective dose equivalents were estimated by using a conversion factor of 6.3 mSv(WLM)"^ (ICRP, 1987). 100 _i I I I 1 I I I I I t_-i—I—L J_ Table 4 presents the radiation risk quantities obtained from 90 100 110 120 130 140 150 238y 232jjj ^^j 40|^ activity concentrations and the radon exhala ^'^h Concentration (Bq kg"^) tion rate. Fig. 4 shows a plot of the variation of ^^*U, ^^^Th, ^°K and Fig. 3. Variation of *'K activity concentration versus ^^^T\\ activity in fly ash samples. absorbed dose rate in different samples. Absorbed gamma dose rate varies from 115.3 to 158.5 nCy h~' were used. The effective dose rate in units of mSvy"' was calcu with a mean value of 126.4 nCy h~' which is ~ 3 times higher than lated by the following relation: the world average (43 nCyh"') as reported by UNSCEAR (1988). Thus the population within 80 km radius of the ash pond may be £ rmSvy-') = Dose rate (nCy h"M x 8760 h x 0.2 exposed to high dose rate. The corresponding outdoor annual xO.7 SvCy-^ X 10" (4) effective doses range from 0.14 to 0.19 mSv. The calculated values of Hex for the fly ash samples studied in this work range from 0.69 to 0.96 (Table 4) and are very close to unity. Since all these values are lower than unity, the fly ash is safe and can be used as a construc 3.3. External hazard index (Hex) tion material without posing significant radiological threat to population. But according to conservative estimate as calculated For limiting the radiation dose from building materials in from Eq. (5), Hex 's close to unity. Thus according to Radiation Germany to 1.5mCyy"\ Krieger (1981) proposed the following Protection 112 (European Commissions, 1999) report care must be relation for Hex'. taken in using the fly ash as building material. j^ Arh. j^ He < 1 (5) 4. Conclusion 370 259 4810" This criterion considers only the external exposure risk due to y- Comparatively high values of activity concentrations of ^^^U, rays and corresponds to maximum Raeq of 370Bqkg~' for the ^^^Th and '"'K in fly ash samples from Durgapur (WB) thermal material. These very conservative assumptions were later corrected power plant are found. Radon exhalation rates are also higher than and the maximum permission concentrations were increased by the fly ash from other power stations of India. There seems to a factor of 2 (Keller and Muth, 1990) which gives a weak correlation between radon exhalation rate and ^^*U activity Av iTh AK He: < 1 (6) Table 4 740Bqkg-' 520Bqkg-' 9620 Bq kg" Radium equivalent activity, absorbed gamma dose rate, effective dose rate, external hazard index and effective dose equivalent in fly ash samples Details Radium At>sorbed Effective Effective External 3.4. Effective dose equivalent (Ep) of equivalent gamtna dose rate. dose hazard samples activity. dose rate. £(mSvy-') equivalent index. Ra«,(Bqkg-') D(nCyh-') (MSvy-') Hex The risk of lung cancer from domestic exposure due to radon irr-Di 2725 122.7 0.15 47.1 0.74 and its daughters can be estimated directly from the effective dose irr-D2 262.8 118.0 0.14 48J2 0.71 equivalents. The risk of lung cancer due to radon and its daughters irr-D3 272.3 116J 0.14 45.0 0.74 is estimated from the radon exhalation rate of fly ash samples. The irr-D4 2563 1153 0.14 55.2 0.69 contribution of indoor radon concentration from fly ash samples irr-DS 257.7 1155 0.14 4a5 0.70 can be calculated from the expression (Nazaroff and Nero, 1988) irr-D6 260.8 1183 0.15 55.4 0.71 irr-D7 334.8 150.1 0.18 42.5 0.91 irr-D8 2635 118.5 0.15 51.6 0.72 CRn (7) irr-D9 352.8 158.5 0.19 45.5 0.96 Vx Av irr-Dio 289.8 1303 0.16 42.7 0.79 where, CRO - radon cot\centration (Bq m~^); E, - radon exhalation Average 282.4 126.4 0.15 47.8 0.77 SD 32.3 14.7 0.02 4.4 0.09 rate (Bq m~^ h~'); V - room volume (m^); Ay - air exchange rate ReLSDX 11.4 11.6 133 9.2 11.6 (h-'). AX Mahur et al /Journal of Environmental Radioactivity 99 (2008) 1289-1293 1293 Fleischer, R.U Morgo-campero. A.. 1978. Mapping of integrated radon emanation for detection of long-distance migration of gasses within the Earth: techniques and principles. Journal of Geophysical Research 83, 3539-3549. Culec. N., Cunal (Caici), B., Erier, A., 2001. Assessment of soil and water contami nation around an ash-disposal site: a case study from the Seyitomer coal fired power thermal plant in western Turkey. Environmental Geology 40 (3), 331-334. Hayambu, R, Zaman, M.B., Lubaba, N.C.H., Munsanje, S.S., Muleya, D.. 1995. Natural radioactivity in Zambian building materials collected from Lusaka. Journal of Radioanalytical and Nuclear Chemistry 199 (3), 229-238. Jojo. P.J, Rawat, A., Kumar, A., Prasad, R., 1993a. Trace uranium analysis in Indian coal samples. Nuclear Geophysics 7, 445-448. jojo, PJ., Rawat, A., Kumar, A., Prasad, R., 1993b. Enhancement of trace uranium in fly ash. Nuclear Geophysics 8, 55-59. Jonassen, N., 1983. The determination of radon exhalation rates. Health Physics 45, 369-374. ICRP, 1987. Lung Cancer risk from indoor exposure to radon daughters. ICRP Publication 50. In: Annals of the ICRP, vol. 17. Pergamon Press, Oxford. Karmadoost, N.A., Durrani, SA, Fremlin, J.H., 1988. An investigation of radon exhalation from fly ash produced in the combustion of coal. Nuclear Tracks and Radiation Measurements 15, 647-650. Keller, G„ Muth, H., 1990. Natural radiation exposure in medical radiology. In: Scherer, E., Streffer, Ch., Tolt, K.R. (Eds.), Radiation Exposure and Occupational Risks. Springer Verlag, Berlin. Khan, A.J., Prasad, R., Tyagi, R.K., 1992. Measurement of radon exhalation rate from some building materials. Nuclear Tracks and Radiation Measurements 20, 2 4 6 8 609-610. Number of Samples Kumar, V.. Ramachandran, T.V., Prasad, R., 1999. Natural radioactivity of Indian building materials and by-products. Applied Radiation and Isotopes 51, 93-96. Fig. 4. Bar diagram showing activity concentration of ^^'U, ^'^ji, and ^K and Kumar, R., Mahur, A.K., Sengupta, D., Prasad, R., 2005. Radon activity and exhalation absorbed gamnna dose rate in different samples. rates measurements in fly ash from a thermal power plant Radiation Measurements 40, 638-641. Krieger, R., 1981. Radioactivity of construction materials. Betonwerk und Fertigteil- Technik 47, 468-473. MacKenzie, A.B., 2000. Environmental radioactivity: experience from the 20th concentration, ^^*U and ^^^Th activity concentration and ^^^Th and century-trends and issues for the 21st century. Science of the Total Environ ^°K concentration. Absorlied radiation doses and external health ment 249, 313-329. hazard from ash studied here are quite high as compared to that of Mandal, A., Sengupta, D., 2003. Radioelemental study of Kolaghat thermal power plant. West Bengal, India: possible environmental hazards. Environmental the other thermal power plants of India but within the limit pre Geology 44, 80-186. scribed by Radiation Protection Agencies and fly ash can be used as Mandal, A.. Sengupta, D., 2005. Radionuclide and trace element contamination building material but with care without posing significant around Kolaghat Thermal Power Station, West Bengal - environmental impli cations. Current Science 88, 617-625. radiological threat to population. Mishra. U.C, Ramchandran, T.V., 1991. Environmental impact of coal utilization for electricity generation. In: Sahoo, K.C. (Ed.), Proceedings of the International Conference on Environmental Impact of Coal Utilization from Raw Materials to Acknowledgments Waste Resources. IIT Bombay, pp. 117-125. Nazaroff, WW., Nero Jr., A.V., 1988. Radon and Its Decay Products in Indoor Air. A The authors wish to thank, the Chairman, Department of Wiley Interscience Publication, New York. Papastefanou, C, Charalanbous, SL, 1979. On the radioactivity of fly ash from coal Applied Physics, Aligarh Muslim University, Aligarh for providing power plants. Zeitschrifl fflr Naturforschung A - A Journal of Physical Sciences the facilities for this work. Prof. Rajendra Prasad wishes to thank All 3, 533-537 India Council of Technical Education, Government of India for Prasad, L, Sharma, C.B., Bhaduri, S.K., 1990. Pollution study of river Canga by providing Emeritus Fellowship to carry out this work. Financial municipal and industrial from waste from Buxar to Bhagalpur with special reference to its effective utilization in water supply management and impacts assistance provided by Department of Science and Technology on public health: a case study from Bihar, Eastern India. In: Proceedings of City (DST), Government of India to Dr. Rajesh Kumar as Young Scientist Water Fronts. Central Water Commission, New Delhi, pp. 8-15. under Fast Track Scheme (Award No. SR/FTP/PS-31/2004) is grate Rao, R.U., 1974. Gamma- ray spectrometric set up at NGRI for analysis of U, Th and K in rocks. Geophysical Research Bulletin 12, 91-101. fully acknowledged. Rawat, A., Jojo, P.J., Khan, A.J., Tyagi, R.K., Prasad, R., 1991. Radon exhalation rate in building materials. Nuclear Tracks and Radiation Measurements 19, 391-394. Singh, A.K., Jojo, P.J., Khan, A.J., Prasad, R., Ramchandran, T.V, 1997 Calibration of References track detectors and measurement of radon exhalation rate from solid samples. Radiation Protection and Environment 3,129-133. Baba, A., 2002. Assessment of radioactive contaminants in by-products from UNSCEAR, 1988. Sources and Effects of Ionizing Radiation. United Nations Scientific Yatagan (Mugia, Turkey) coal-fired power plant. Environmental Geology 41, Committee on the Effect of Atomic Radiation. United Nations, New York. 916-921. UNSCEAR, 1993. Sources and Effects of Ionizing Radiation. United Nations Scientific Bem, H., Wieczorkowski, P., Budzanoswki, 2002. Evaluation of technologically Committee on the Effect of Atomic Radiation, United Nations, New York. enhanced natural radiation near the coal-fired power plants in the Lodz region UNSCEAR, 2000. Sources and Effects of Ionizing Radiation. United Nations Scientific of Poland. Journal of Environmental Radioactivity 6,191-201. Committee on the Effect of Atomic Radiation. United Nations, New York. Eisenbud. M, Cesell, T, 1997. Environmental Radioactivity, fourth ed. Academic Vijayan, V., Behra, S.N., 1999. Studies on natural radioactivity in coal ash. In: Press. San Diego. Mishra. P.C. Naik, A. (Eds.), Environmental Management in Coal Mining and EC. 1999. European commission report on radiological protection principles con Thermal Power Plants. Technoscience, Jaipur, pp. 453-456. cerning the natural radioactivity of building materials. Radiation Protection 112. Yu. K.N., Cuan, Z.J., Stokes, M.J., Young, E.CM.. 1992. The assessment of natural El-Arabi. A.M.. 2005. Gamma aaivity in some environmental samples in South radiation dose committed to Hong Kong people. Journal of Environmental Egypt. Indian Journal of Pure and Applied Physics 43, 422-426. Radioactivity 17,31-48. Available online at www sciencedirect com Applied ScienceDirect Radiation and Isotopes ELSEVIER Applied Radiation and Isotopes 66 (2008) 401 406 www elsevier com/locate/apradiso An investigation of radon exhalation rate and estimation of radiation doses in coal and fly ash samples A.K. Mahur*'*, Rajesh Kumar^, Meena Mishra^, D. Sengupta^, Rajendra Prasad^ ^Department of Applied Physics ZH College of Engineering and Technology Altgarh Muslim University Aligarh 202002 India ^Department of Geology and Geophysics IIT Kharagpur Kharagpur 721362 India Received 5 December 2006, received in revised form 8 August 2007, accepted 14 October 2007 Abstract Coal IS a technologically important matenal used for power generation Its cinder (fly ash) is used in the manufactunng of bncks, sheets, cement, land filhng etc Coal and its by-products often contain sigmficant amounts of radionuchdes, including uranium which is the ultimate source of the radioactive gas radon Burning of coal and the subsequent atmosphenc emission cause the redistnbution of toxic radioactive trace elements in the environment In the present study, radon exhalation rates in coal and fly ash samples from the thermal power plants at Kolaghat (W B) and Kasimpur (UP) have been measured using sealed Can technique having LR-115 type II detectors The activity concentrations of'^^^U, ^^^Th, and '"'K in the samples of Kolaghat power station are also measured It is observed that the radon exhalation rate from fly ash samples from Kolaghat is higher than from coal samples and activity concentration of radionuclides in fly ash is enhanced after the combustion of coal Fly ash samples from Kasimpur show no appreciable change in radon exhalation Radiation doses from the fly ash samples have been estimated from radon exhalation rate and radionuclide concentrations © 2007 Elsevier Ltd All nghts reserved Keywords Radon exhalation rate, Gamma ray spectroscopy, LR-115 type II detector. Radium eqmvalent acUvity, Gamma absorbed dose to air rates 1. Introduction Radon exhalation rate from fly ash is of prime importance for the estimation of radiation nsk Earlier studies (Mishra, Thermal power generation contnbutes more than 70% 2004) on coal and fly ash have shown that Indian coals of the power generation in India Indian coal is of contained 1 8-6 0ppm "^U and 6 0-15 0ppm of "^Th bituminous type with 55-60% ash content amounting to Recent studies have indicated as high as 50 ppm ^^^Th and 100 million tons of fly ash per year (Vijayan and Behra, lOppm of ^^*U in the pond ash generated from coal 1999) Like other natural matenals, coal contains U, Th, combustion (Mandal and Sengupta, 2003) Radiation risk and K radionuclides, which may be concentrated in the fly from fly ash is of importance since if used m construction ash by thermal power plant combustion Also, coal matenals it may raise the concentration of airborne indoor combustion may enhance the natural radiation in the radioactivity to unacceptable levels, especially in places vicinity of the thermal power plant through the release of having low ventilation rates (Rawat et al, 1991, Khan et the radionuclides and their daughters in the surrounding al, 1992) In the present study, radon exhalation rates from ecosystem such as the surface soil Due to diverse uses of fly the coal and fly ash samples collected from the thermal ash in building matenals, as under ground cavity filhng power stations at Kolaghat and Kasimpur situated in West matenal and in the production of cement, etc , fly ash has Bengal and Uttar Pradesh states of India have been become a subject of worldwide interest in recent years measured to estimate their enhancement in fly ash due to coal combustion Also the activity concentrations of ^^*U, 'Corresponding author Tel +915712742837, +919412808481 ^^^Th, and '*°K radionuclides in the samples of Kolaghat (mobile) power station are measured using a low level Nal (Tl) E-mail address ajaymahur345@rediffmail com (A K Mahur) gamma ray spectrometer (Mandal and Sengupta, 2003) 0969-8043/$-see front matter © 2007 Elsevier Ltd All nghts reserved doi 10 1016/j apradiso 2007 10 006 402 A.K. Mahur et al. / Applied Radiation and Isotopes 66 (2008) 401-406 Radiation doses and health risk have been estimated from 2. Experimental method the radon exhalation and ^^^U, ^^, and ^ concentrations. 2.1. Radon exhalation rate 1.1. Geology of study area Samples of coal and fly ash were collected from The Kolaghat thermal power plant is situated in the Kolaghat and Kasimpur thermal power plants. Coal Midnapur district of West Bengal and near Mecheda samples were grinded. All the samples were dried and railway station on the South-Eastem Railway route. It is sieved through a 100-mesh sieve. Sealed Can technique was 59 km away from Kharagpur in the ENE direction and used for the radon exhalation measurements. In such 60 km WSW of Kolkata. Fig. 1 shows the location map of measurements equal amount of each sample (lOOg) was Kolaghat thermal power plant, West Bengal, India. The placed in the Cans (diameter 7.0 cm and height 7.5 cm) Kolaghat region falls within the Kasai delta of Contai similar to those used in the calibration experiment (Singh et formation of late Pleistocene age. The dominant lithotypes al., 1997). In each Can, an LR-115 type II plastic track of the Contai formation are laterite, with mottled red and detector (2 cm x 2 cm) was fixed at the top inside of the brown clays at the top. The major surface runoff in the Can. Thus the sensitive lower surface of the detector is region is the Denan-Dehati canal, which is the major outlet freely exposed to the emergent radon so that it is capable of of the Rupnarayan River, and lies to the west of the recording the alpha particles resulting from the decay of thermal power plant. The Kasai River is the principal radon in the Can. Radon and its daughters reach an tributary of the Haldi River and enters the study areas equilibrium concentration after a week or more and thus from the north-west. The Denan-Dehati canal and a the equilibrium activity of emergent radon could be branch of the Kasai River are the major sources of portable obtained from the geometry of the Can and the time of water to about 100,000 people in the neighboring 200 exposure. The half life of thoron is very small and ^^°Rn villages of the Kolaghat, Delta and Panskura blocks in has lower exhalation rate/emanation factor. Also ^^^Th West Bengal. Kasimpur thermal power plant (KTPP) is concentration is low and is comparable with ^^^U in the situated in the plains of the state of Uttar Pradesh and the present case. Therefore, the tracks recorded in TE detector wastes are discharged into the upper Ganges canal. due to alpha particles may be attributed to '^^^Rn escaping 25 50 kin L -J Scale Kasiinpiu- thennal power plant {U P) Iiulia Kolagliat thennal power plant (W.B ) IiwUa Muwrn Fig. 1. L,ocation map of Kasimpur thermal power plant (U.P.) and Kolaghat thennal power plant (W.B.), India. A.K. Mahur et al. / Applied Radiation and Isotopes 66 (2008) 401^06 403 from the sample as very small number of ^^'^Rn may be able thorium (with a little uranium), (2) containing only to escape from the sample. uranium, and (3) containing only potassium. In the present After the exposure for 100 days, the detectors from all laboratory set-up, the standard samples were prepared the Cans were retrieved. The detectors were etched in 2.5 N using powders obtained from the US NRC, New Bruns NaOH at 60+1 °C for a period of 90 min in a constant- wick Laboratory. The error in the measurement of temperature water bath to reveal the tracks. Resulting concentration is 5%. Assaying was carried out by the alpha tracks on the exposed face of the detector foils were method followed at the National Geophysical Research scanned under an optical microscope at a magnification of Institute, Hyderabad. The details of the method of assaying 400 X . From the track density, the radon activity was are given elsewhere (Rao, 1974; Mandal and Sengupta, obtained using the cahbration factor of 0.056Trcm~^d"'' 2003, 2005). (Bqm~^)~' obtained from an earlier calibration experiment (Singh et al., 1997). The calibration experiment was 3. Result and discussion performed at Environmental Assessment Division of Bhabha Atomic Research Centre, Mumbai, India. Experi Values of radon activity and radon exhalation rates from mental set-up used is well known for its performance and coal and fly ash samples are presented in Table 1 along accuracy (Subba Ramu et al., 1990; Jojo et al., 1994). with their ^^^U, ^^^Th, and '"'K activity concentration. As Calibration was done under the simulated conditions like already pointed out (Mandal and Sengupta, 2005), coal those present in the experiment. The details are given and fly ash from the Kolaghat power station has a higher elsewhere (Jojo et al., 1994; Singh et al., 1997). Following concentration of radionuclides compared to other power expression gives the exhalation rate (Khan et al., 1992; plants in India and coal combustion enhances the radio Fleischer and Morgo-campero, 1978; Kumar et al., 2003, activity in fly ash. In coal samples, radon activities were 2005): found to vary from 0.86 to 2.86kBqm~^ with an average value of l.SSkBqm"', whereas the radon exhalation rate CVk £,= (1) varied from 0.31 to 1.03Bqm~'^h~' with an average value ^4[r + (l/A){e-^^-l}]' of 0.67 Bqm"^h"'. While in fly ash samples, ^^^Rn activity where E,^ is radon exhalation rate (Bqm~^h~'), C is is found to vary from 3.05 to 4.31 kBqm~^ with an average integrated radon exposure as measured by LR-115 type II value of 3.64 kBqm"^, whereas the ^^^Rn exhalation rate plastic track detector (Bq m~^ h), V is effective volume of varied from 1.10 to 1.55Bqm~^h~' with an average value Can (m''), k is decay constant for radon (h~'), Tis exposure of 1.31 Bqm~^h~'. In coal samples, activity concentrations time (h), and A is area covered by the Can (m^). of ^^^U ranged from 25 to 49 Bq kg"' with an average value The errors in radon exhalation rate depend on the track of 37 Bqkg~\ ^^^h ranged from 39 to 55 Bqkg"' with an density and are always <5%. average value of 49Bqkg"' and '*"K ranged from 124 to 155 Bq kg"' with an average value of 130 Bq kg"'. While in 2.2. Radiometric analysis fly ash samples ^^^U ranged from 99 to 120 Bq kg"' with an average value of 113Bqkg"', ^•'^Th ranged from 126 to For radiometric analysis, coal and fly ash samples 147Bqkg"' with an average value of 141 Bqkg"' and '^K collected from Kolaghat thermal power plant were stored ranged from 210 to 334Bqkg"' with an average value of in polyethylene bags. They were dried for 24 h in an air- 278 Bqkg"'. circulation oven at 110 °C. About 250 g of each sample was The results for the values of the radon activity and radon packed in plastic containers and sealed for 15 days before exhalation rates in the coal and fly ash samples from counting for ^^^U and ^^^Th to attain secular equilibrium KTPP, Kasimpur are presented in Table 2. In coal samples, with their decay products and to prevent ^^^Rn and ^^"Rn radon activity is found to vary from 1.99 to 4.07 kBqm"^ loss. A low-level gamma ray spectrometric set-up at the with an average value of 3.18kBqm~^, whereas the radon National Geophysical Research Institute, Hyderabad, was exhalation rate varies from 0.71 to 1.46 Bqm"^h"' with an used for the estimation of "^U, ^^^Th and ''"K. The average value of 1.17Bqm"^h"'. While in fly ash samples, detector consisted of a 5 in. x 6 in. Nal (Tl) crystal coupled radon activity is found to vary from 1.50 to 4.10kBqm"^ to a 5 in. diameter photomultiplier tube. A 256-channel with an average value of 3.02 kBqm"^, the radon exhala data set covering 0-3 MeV is obtained through a multi tion rate varies from 0.54 to 1.48Bqm~^h"' with an channel analyzer (MCA) card (on a computer) that average value of 1.09Bqm"^h"'. provided a gain-stabilized spectrum. ^^*U and ^^^Th were From Table 1, it can be observed that the radon assessed from the intensity of the gamma ray peaks of their exhalation rate and radionuclides concentration in fly ash daughters: ^"*Bi (1.76 MeV) and ^"^Tl (2.62 MeV), assum samples are higher than coal samples from Kolaghat. Table ing all daughter products are in equilibrium whereas '"^K 2 shows no appreciable change in radon activity and radon was measured directly from its own gamma ray of exhalation rate from fly ash samples from Kasimpur. It is 1.46 MeV. The samples were analyzed for a very long worth mentioning that it is difficult to predict the radon counting time (generally 2-3 h). The standard samples with exhalation rate from the concentration of uranium or its which the set-up needs to be calibrated are (1) containing decay series products in the sample, since the radon 404 A fC Mahur et al / Applied Radiation and Isotopes 66 (2008) 401-406 Table 1 Radon activity concentration, radon exhalation rate, and activity concentration of radionuclides in coal (C-X) and fly ash (FA-A^ samples from Kolaghat thermal power plant (West Bengal) Sample Radon emanation Activity concentration Radon activity Radon exhalation rate '''U(Bqkg-') 2'^Th(B C-1 196 0 70 37 48 124 C-2 2 74 0 98 38 53 155 C-3 0 98 0 35 36 48 124 C-4 0 86 031 25 39 124 C-5 2 86 103 49 55 124 Average value 188 0 67 37 49 130 SD 0 84 0 30 8 6 12 R S D % 447 45 5 22 12 9 FA-1 3 62 1 30 117 146 334 FA-2 3 39 122 120 147 231 FA-3 4 15 149 115 144 234 FA-4 3 52 126 117 143 210 FA-5 3 28 1 18 99 142 308 FA-6 3 05 1 10 110 147 226 FA-7 4 09 147 118 136 308 FA-8 3 10 1 12 108 136 306 FA-9 431 1 55 114 126 298 FA-10 391 140 108 139 319 Average value 364 1 31 113 141 278 SD 0 43 0 15 6 6 44 R S D % 118 11 5 5 4 16 Table 2 exhalation rate depends also on the texture and grain size Radon activity concentration, radon exhalation rate, and indoor composition (Tufail et al., 1991). As fly ash is frequently inhalation exposure (radon)-effective dose in coal (KP-C) and fly ash used as building material in different forms, it is important (KP-F) samples from Kasimpur thermal power plant (UP) to assess the radiation risk to public. Sample Radon Radon Indoor inhalation activity exhalation rate exposure (radon)- 3.1. Radium equivalent activity (ROeq) (kBqm"') (Bqm'^h"') effective dose (mSvyr"') Exposure to radiation is defined in terms of radium KP-Cl 3 68 132 0 149 equivalent activity (Raeq) in Bqkg~' to compare the KP-C2 3 19 1 15 0 129 specific activity of materials containing different amounts KP-C3 199 071 0 080 of ^^^U, ^^^Ra, ^^^Th, and '^''K. From A^j, A-n, and Ay^, for KP-C4 2 19 0 79 0 089 KP-C5 3 31 1 19 0 134 the activity concentrations of ^^*U, ^"Xh, and '"'K in KP-C6 4 07 146 0 165 Bqkg"', respectively (Yu et al., 1992), Ragq can be KP-C7 3 62 130 0 146 calculated as KP-C8 2 85 1 03 0 115 KP-C9 3 75 1 35 0 152 Raeq =Au + 1.43^Th + O.OT^K- (2) Average value 3 18 1 17 0 128 There are variations in the radium equivalent activities SD 0 67 0 24 0 27 of different materials and also within the same material R S D % 0 21 0 02 212 type. These results may be important from the point of KP-Fl 3 25 1 17 0 131 view of selecting suitable materials for use in building KP-F2 150 0 54 0 061 construction. KP-F3 2 90 104 0 117 KP-F4 4 10 148 0 166 KP-F5 3 62 130 0 146 3.2. Outdoor external exposure due to gamma radiation (D) KP-F6 2 89 104 0117 KP-F7 3 52 127 0 142 The gamma absorbed dose to air rates (D) in air at 1 m 0 095 KP-F8 2 36 0 85 above the ground surface for the uniform distribution of Average value 3 02 1 09 0 121 radio nuclides ("^Th, "^U, and '^K) are calculated on the SD 0 76 0 27 0 030 basis of guidelines given by UNSCEAR (1988). The dose 0 025 R S D % 0 03 0.03 conversion factors for converting the activity concentra- A K Mahur et al / Applied Radiation and Isotopes 66 (2008) 401-406 405 tions of ^^^U, "^Th, and •*°K into doses (nGyh"' CRH = (5) per Bqkg"') are 0.462, 0.604, and 0.0417, respectively. FxAv' Thus where CRJ,, E^, S, V, and iv are radon concentration D = (0.462^u + 0.604^Th + 0.04 17^K) nGyh" (3) (Bqm"^), radon exhalation rate (Bqm"^h~'), radon exhalation area (m^), room volume (m^), and air exchange The mean dose rate as computed from the above rate (h~'), respectively. equation is found to be 148nGyh ' which is about three In these calculations, the maximum radon concentration K times higher than the world average (51nGyh~') as from the building material was assessed by assuming the reported by UNSCEAR (1988). To estimate the annual room as a cavity with SIV= 2.0 m~' and air exchange rate effective dose rates, the conversion coefficient from gamma of 0.5h~'. The annual exposure to potential alpha energy absorbed dose in air to effective dose (0.7SvGy~') and Ep (effective dose equivalent) is then related to the average outdoor occupancy factor (0.2) proposed by UNSCEAR radon concentration CRJ, by the following expression: (1988) were used. The effective dose rate was calculated by the following relation: 8760 X n X F X CRD £p(WLMyr-') = (6) 170 X 3700 '- Effective dose rate (mSvyr"') where CRH is in Bqm~^; n, the fraction of time spent = Gamma dose rate (nGyh"') x 8760h x 0.2 indoors; 8760, the number of hours per year; 170, the x0.7SvGy"' X 10-^ (4) number of hours per working month, and F is the equilibrium factor for radon. Radon progeny equilibrium 3.3. Indoor internal exposure due to radon inhalation is the most important quantity when dose calculations are to be made on the basis of the measurement of radon The risk of lung cancer from domestic exposure of ^^^Rn concentration. Equilibrium factor F quantifies the state of and its daughters can be estimated directly from the indoor equilibrium between radon and its daughters and may have inhalation exposure (radon)-effective dose. The contribu values 0 < F< 1. The value of F is taken as 0.4 as suggested tion of indoor radon concentration from fly ash samples by UNSCEAR (1988). Thus the values of « = 0.8 and can be calculated from the expression (Nazaroff and Nero, F = 0.4 were used to calculate Ep. From radon exposure, 1988): the indoor inhalation exposure (radon)-effective dose were Table 3 Radium equivalent activity, gamma absorbed dose to air rate, outdoor external exposure, indoor inhalation exposure (radon)-effective dose in coal (C-^O. and fly ash (FA-Jf) samples from Kolaghat thermal power plant (West Bengal) Details of samples Radium equivalent Gamma absorbed dose to Outdoor external Indoor inhalation activity, Ra^q air rate. /)(nGyh-') exposure (mSvyr~') exposure (radon)- effective dose (mSvyr"') C-1 114 51 0 09 0 079 C-2 125 56 0 10 OHO C-3 113 51 0 09 0 039 C-4 90 40 0 07 0 035 C-5 136 61 • 0 10 0 116 Average value 116 52 0 09 0 076 SD 16 7 0 01 0 034 R S.D % 13 13 118 0044 FA-1 349 156 0 19 0 146 FA-2 346 153 0 19 0 136 FA-3 337 150 0 18 0 167 FA^ 336 145 0 18 0 142 FA-5 323 144 0 17 0 124 FA-6 336 149 0 18 0 123 FA-7 334 150 0 18 0 165 FA-8 324 145 0 17 0 125 FA-9 315 141 0 17 0 174 FA-10 329 147 0 18 0 157 Average value 333 148 0 18 0 146 SD 10 4 0 01 0018 R S D % 3 3 55 0 013 406 A K. Mahur et al / Applied Radiation and Isotopes 66 (2008) 401-406 estimated by using a conversion factor of 6 3 mSv WLM~' References (ICRP, 1987) Table 3 presents the radiation nsk quantities obtained from ^^^U, ^^^Th, and ''"K activity concentrations Fleischer, R L, Morgo-campero, A, 1978 Mapping and integrated and from radon exhalation rates for Kolaghat samples In radon emanation for detection of long distance migration of gasses Table 2, the indoor inhalation exposure (radon)-efi"ective with in the earth, techniques and pnnciples Geophys Res 83, 3539-3549 dose for the samples from Kasimpur are presented and ICRP, 1987 International Commission on Radiological Protection vary from 0 080 to 0 165 mSv yr~' with an average value of Publication No 50, 17, New York 0 128 mSv yr~' m coal samples whereas in fly ash samples it ICRP, 2007 International Commission on Radiological Protection, New is found to vary from 0 061 to 0 1 66mSvyr~^ with an York average value of 0 121 mSvyr"' Jojo, P J , Khan, A J , Tyagi, R K , Prasad, R , Ramchandran, T V , Subba Ramu, M C , Prasad, R , 1994 Interlaboratory calibration of track-etch detectors for the measurement of radon and radon daughter 4. Conclusion levels Radiat Meas 23, 715-724 Khan, A J, Prasad, R, Tyagi, RK, 1992 Measurement of radon The radon activity, radon exhalation rate, and activity exhalation rate from some buildmg matenals Nucl Tracks Radiat Meas 20, 609-610 concentration of radionuclides of the fly ash from Kumar, R, Sengupta, D , Prasad, R, 2003 Natural radioactivity and Kolaghat are higher than coal samples and also of fly ash radon exhalation studies of rock samples from Surda deposits in from other power plants, i e from Kasimpur Gamma Singhbhum shear zone Radiat Meas 36, 551-553 absorbed dose rate is three times higher than the world Kumar, R , Mahur, A K , Sengupta, D , Prasad, R , 2005 Radon activity average Thus the population within 80 km radius of the and exhalation rates measurements in fly ash from a thermal power plant Radiat Meas 40, 638-641 ash store may be exposed to higher dose rate The Mandal, A , Sengupta, D, 2003 Radioelemental study of Kolaghat corresponding outdoor annual effective dose ranges from thermal power plant, West Bengal, India possible environmental 0 07 to 0 lOmSv in coal samples, whereas in fly ash samples hazards Environ Geol 44, 80-186 It IS found to vary from 0 17 to 0 19mSv with an average Mandal, A, Sengupta, D, 2005 Radionuchde and trace element value of 0 18mSv Indoor inhalation exposure (radon)- contamination around Kolaghat Thermal Power Station, West efTective dose from fly ash collected from both the power Bengal—environmental implications Curr Sci 88, 617-625 Mishra, U, 2004 Environmental impact of coal industry and thermal plants IS less than 0 3mSvyr~', the dose constraint (ICRP, power plants in India J Environ Radioact 72, 34-40 2007) based assessment, e g with ^^ax Thus, the fly ash Nazaroff, W W , Nero Jr , A V , 1988 Radon and Its Decay Products in appears to be safe and may be used as a construction Indoor Air Wiley Interscience, New York matenal without posing significant radiological threat to Rao, R U , 1974 Gamma ray spectrometnc set up at NGRI for analysis population of U, Th, and K in rocks Geophys Res Bull 12,91 101 Rawat, A , Jojo, P J , Khan, A J , Tyagi, R K , Prasad, R , 1991 Radon Radon activity and radon exhalation of the fly ash exhalation rate m building matenals Nucl Tracks Radiat Meas 19, samples from Kolaghat thermal power plant are higher 391-394 than coal samples and also from fly ash samples from other Singh, A K , JOJO, P J , Khan, A J , Prasad, R, Ramchandran, T V , 1997 thermal power plants of India, i e KTTP, Kasimpur Calibration of track detectors and measurement of radon exhalation rate from sohd samples Radiat Prot Environ 3, 129-133 Gamma absorbed dose rate is three times higher than then Subba Ramu, M C , Shaikh, A N , Murleedharan, T S , Rammchandran, the world average Thus, the population withm 80 km T V , 1990 Measurment of equihbnum factor for ^^^Rn daughters in radius of the ash store may be exposed to higher dose rate dwelhngs in India Sci Total Environ 99, 49-52 Tufail M , Mirza, S M , Chughati, M K , Ahmad, N , Khan, H A , Acknowledgments 1991 Prehminary measurements of exhalation rates and diffusion coefficients for radon in cements Nucl Tracks Radiat Meas 19, 427^28 The authors are thankful to Kolaghat and Kasimpur UNSCEAR, 1988 Sources and Effects of Ionizing Radiation Umted thermal power plant authonties for providing coal and fly Nations Scientific Committee on the Effect of Atomic Radiation, ash samples R P thanks All India Council of Technical United Nation, New York Education, Govt of India for providing an Emeritus Vijayan, V, Behra, SN, 1999 In Naik, A (Ed), Environmental Management in Coal Mining and Thermal Power Plants Tech- Fellowship to carry out this work Financial assistance noscience, Jaipur, pp 453-456 provided by Department of Science and Technology, Govt Yu, K N , Guan, Z J , Stokes, M J , Young, E C , 1992 The assessment of of India to R K as a Young Scientist under the Fast Track natural radiation dose comimtted to Hong Kong people J Environ Scheme (Award no SR/FTP/PS-31/2004) is gratefully Radioact 17, 31-48 acknowledged Available online at vvww.sciencedirect.com *••' ScienceDirect mm^ wMi Matoftate A Atoms ELSEVIER Nuclear Instruments and Methods in Physics Research B 266 (2008) 1591-1597 www elsevier com/locate/nimb Measurement of natural radioactivity and radon exhalation rate from rock samples of Jaduguda uranium mines and its radiological implications A.K. Mahur", Rajesh Kumar ^, R.G. Sonkawade'', D. Sengupta^ Rajendra Prasad''• " Department uf Applied Physii \ Z H College of Engineering and Tei hnulogy Aligarh Muilim Univenily Aligarh 202 002 India ^liiter-Universitv Accelerator Centre Aruiiu AiafAli Marg New Delhi 110 067 India ''Department of Geolog\ and Gevphy\Hs Iiuliaii ln\titute u] Teilinologv Kharagpiir 721 302 India Received 24 September 2(X)7. received m revised form 10 January 2008 Available online 2 February 2008 Abstract The Singhbhum shear zone is a 200 km long arcuate belt in Jharkhand state situated in eastern India The central part between Jadug- uda-Bhatin-Nimdih, Narwapahr-Garadih-Turamdih is rich in uranium Presence of uranium in the host rocks and the prevalence ol a confined atmosphere withm mines could result in enhanced concentration of radon (^^^Rn) gas and its progeny Inhalation of radon daughter products is a major contributor to the radiation dose to exposed subjects By using high resolution y-ray spectroscopic system various radionuclides in the rock samples, collected from different places of Jaduguda uranium mines have been identified quantitatively based on the characteristic spectral peaks The activity concentrations of the natural radionuckdes, uranium (''*UJ, thorium (^^"Th) and potassium (""K) were measured in the rock samples and radiological parameters were calculated Uranium concentration was found to vary from 12^ ± 7 Bq kg"' to 40,858 ± 174 Bq kg"' Activity of thorium was not significant m the samples, whereas, few samples have shown potassium activity from 162 ± 11 Bq kg 'to 9024 ± 189 Bq kg ' Radon exhalation rates from these samples were also measured using "Sealed Can technique" and found to vary from 42±0 05tol37±0 08Bqm""h"' A positive correlation was found between the radon exhalation rate and the uranium activity The absorbed dose rates vary from 63 6 to 18876 4 nGy h"', with an average value of 7054 2 nGy h~' The annual external effective dose rates vary from 0 7 to 23 2 mSv y"' Radium equivalent activities (Ra^) varied from 134 3 to 40858 OBq kg"' Value of external hazard index (//„) varied from 0 4 to 110 4 with an average value of 41 2 © 2008 Elsevier B V All rights reserved PACS 92 20Td. 92 60 Sz. 29 40 Wk KeyHordi Natural riidioaclivit) Uranium mines. Uranium concentration Radon exhalation rale. HPGe low level radiation counting system I. Introductiun in rocks, soils, building materials, water and atmosphere Some of the radionuclides from these sources may be trans TJie knowledge of radionuclides distribution and radia ferred to human beings through food chain or inhalation tion levels in the environment is important for assessing the The exposure of human beings to ionizing radiations takes effects of radiation exposure to human beings due to both place due to naturally occurring radioactive elements in the terrestrial and extra terrestrial sources Terrestrial radia solids and rocks, cosmic rays entering the earth's atmo tion is due to the radionuclides present m different amounts sphere from outer space and also the internal exposure from radioactive elements through food, water and air Natural radioactivity is wide-spread in the earth's environ CorrcsfKinding author Tel +91 571 2742817/941280X481 E-mail «iA/rivw\ RjaymahurM5 OI68-583X/$ - see from mailer ' 2008 Elsevier B V All rights reserved doi 10 1016/j nimb 2008 01 056 «fi:^Sl 9 1592 A.K. Mahur et al.lNucl. Inslr. and Melh. in Phys. Res. B 266 (2008) 1591-1597 Tonnations like soils, rocks, plants, water and air [1-6]. Banguridih and Jaduguda and continue through the ura Radiological implication of these radionuclides is due to nium and copper deposits of Surda-Roam, Rakha-Mosa- the gamma ray exposure of the body and ot-irradiation of bani and Bagjata-Kanyakula-Dumardiha in the adjoining lung tissues from inhalation of radon and its daughters. Mayurbhanj district of the state of Orissa, India. The shear The assessment of gamma radiation dose and radon exha zone was active over a long period of time from 2000 to lation rate from natural sources is of particular interest as 700 Ma and has been the loci for volcanism and for the natural radiation is the largest contributor to external dose emplacement of basic intrusives and potassium and soda- of the world population [7,8]. Radon, an- radioactive inert rich granites [13]. gas is associated with the presence of radium and its ulti Jaduguda mines located almost in the middle of the mate precursor uranium. Naturally occurring heaviest Singhbhum shear zone contain the richest U deposit in radioactive toxic element uranium is found in traces in the entire belt and have been mined for its uranium ore almost all types of rocks, soils, sands and water. As it for almost two decades. Two uraniferous ore bodies, can get dissolved in aqueous solutions in hexavalent 60 m apart are delineated at Jaduguda and these are com (U*"*") form and can be precipitated as a discrete mineral monly referred to as fort wall lode or the central Jaduguda in tetravalent (V**) form. Uranium may form deposits in lode and the Hang-wall lode or the Eastern Jaduguda lode. the earth's crust where the geological conditions become The host rock for the mineralization is an apatite-magne- favorable. Although these radioactive elements occur in tite-tourmaline-biotite-chlorite bearing quartz-rich schist. virtually all type of rocks and soils, their concentrations The grade of the ore increases from an average of 0.067% vary with specific sites and geological compositions. Short UjOg to about 0.20% UjOg. The mineralization of uranium lived radon progenies have been established as causative has been found to exist up to a depth of 800 m. It continues agents of lung cancer [7,9]. Under specific conditions such even deeper, though at the deeper levels it is affected by a as those prevailing in the uranium mining environment major fault. The Narwapahr uranium deposit has a larger lung dose due to radon progenies may be sufficiently high. spatial extent with a total strike length being estimated to Growing world wide interest in natural radiation has lead be more than 3 km [14] to extensive surveys in many countries. External gamma dose estimation due to terrestrial sources is essential not 3. Experimental only due to its considerable contribution (0.46mSvy~') to collective dose but also because of the variations of indi 3.1. Radiometric analysis vidual doses related to its path ways. These doses vary depending upon the concentrations of the natural radio 3.1.1. Estimation of-^^U, "'Th and ^K nuclides U and ^'^Th and their daughter products and Rock samples were collected from different places far ^'K, present in the soils and rocks which in turn depend apart in the Jaduguda uranium mines in the shear zone. upon the local geology and region in the world [10,1 l].To After collection, samples were crushed into fine powder evaluate the radon risk in a given atmosphere it is necessary by using Mortar and Pestle. Fine quality of the sample is to identify and localize its sources. In the present study low obtained by using scientific sieve of 150 micron-mesh size. level gamma ray spectroscopy was used for the estimation Before measurements samples were oven dried at 110 "C of U, Th and K concentration (Cu. CTH and CK) in the for 24 h and the samples were then packed and sealed in rock samples collected from different places of Jaduguda an impermeable airtight PVC container to prevent the uranium mines in Singhbhum shear zone in the state of escape of radiogenic gases radon (^^^Rn) and thoron Jharkhand, India. Solid State Nuclear track detectors were (^^"Rn). About 300 g sample of each material was used applied for the measurement radon exhalation rates. for measurements. Before measurements, the containers Gamma dose was estimated from the activity concentra were kept sealed about four weeks in order to reach equi tion of natural radionuclides ^'"U, ^"Th and ""K. librium of the ^'*U and ^'^Th and their respective proge nies. After attainment of secular equilibrium between 2. Geology of the study area ^'"U and ^'^ Th and their decay products, the samples were subjected to high resolution gamma spectroscopic analysis. The Singhbhum shear zone is 200 km long arcuate belt Gamma ray spectrometric measurements were carried in the state of Jharkhand State of India. Fig. I shows a geo out at Inter-University Accelerator Centre, New Delhi logical map of the Singhbhum shear zone. Wide-spread using a coaxial n-type HPGe detector (EG&G, ORTEC, uranium mineralization is found to be associated with Oak Ridge, USA). The detector having a resolution of copper, nickel, molybdenum and other sulphides. The 2.0 keV at 1332 keV and a relative efficiency of 20% was south-eastern part of the shear zone between Tampahar- placed in 4 in. shield of lead bricks on all sides to reduce Roam-Rakha and Surda-Mosabani-Badia is rich in cop the background radiation from building materials and cos per mineralization with major deposits, whereas the central mic rays [15] The detector was coupled to a PC based 4 K part between Jaduguda-Bhatin-Nimidih, Narwapahr- multi channel analyzer and an ADC for data acquisition. Garadih-Turamidh and Mahuldih are rich in uranium The calibration of the low background counting system [12,13]. Major uranium occurrences are found between was done with a secondary standard which was calibrated A K. Mahur el at INucI Instr and Meth in Phys Res B 266 (2008) 1591-1597 1593 PAKCTTAN SugUkw Skear Za> StaiyArea N 1c maNagarR.S i"4fc<^SSi. - Naiwapaliar Bhatki *<»1 ^ ^'i?^^ Jaduguda * • « • • « »«••••» **• « * • « * « • • * • • . ^^x IhDEX 553 «-*• \^ I ISehsb A Qoutat* (Sia^Unm ' ' Ooop) Con|Vanu>li- x \ jGnp 'VsPagjata Fig I Geologiuil map of the Singhbhum shear zone. Jharkhand stale with copper and uranium minerahzation With the primary standard (RGU-1) obtained from the ^"*Pb 295 and 352 keV and ^'"Bi 609,1120 and 1764 keV international atomic energy agency (IAEA) The efficiency whereas for ^'^Th were "'Ac 338, 463, 911 and 968 keV, for the system was determined using secondary standard -'^Bi 727keV,2'^Pb 238 keV and ^'"Pa 1001 keV gamma source of uranium ore in the same geometry as available ray by assuming the decay series to be in equilibrium [16]. for the sample counting. For activity measurements the Weighted averages of several decay products were used to samples were counted for a period of 72,000 s The activity estimate the activity concentrations of ^'"U and ^'"Th concentration of "**' K (CK) was measured directly by its The spectra were analyzed using the locally developed soft own gamma ray of 1461 keV As •^""U and ^^^Th are not ware "CANDLE (Collection and analysis of nuclear data directly gamma emitters, their activity concentrations (C^i using Linux net work)" and Cxh) were measured through gamma rays of their The net count rate under the most prominent photo decay products Decay products taken for ^^*U were peaks of radium and thorium daughter peaks are calculated IS94 A.K. Mahur el al. INucl. Instr. and Mtlh. in Phys. Res. B 266 (2008) 1591-1597 from respective count rate after subtracting the back ground counts of the spectrum obtained for the same counting time. Then the activity of the radionuclide is cal culated from the backgroiuid subtracted area of prominent LIM15- gamma ray energies. Gamma ray spectrum of one typical rock sample is shown in Fig. 2. The concentration of ura nium, thorium and potassium is calculated using the fol lowing equation: PlafrticCui-^ 7^ . •• ,,. . -u (5± 3.2. Radon exhalation rate < W ^ "Sealed can technique" [2,3,17] was adopted for radon exhalation measurements. LR-115 Type II plastic track Fig. 3. Assembly for the measurement of radon exhalation rate using detector (2 cm x 2 cm) was fixed on the top inside the "sealed can technique". cylindrical Can of 4.S cm height and 7.0 cm diameter as shown in Fig. 3. Equal amount of each sieved (100 urn Jadnftuaa samplM JAD2, JADS, JADI, JAD6 I I I I I I I I I I I I I I I i e U tNI.( t3UJ ITlit 2M11 S73J Energy (keV) Fig 2 Spectra of the rwk samples from Jaduguda uranium mines (II JAD 2. (2) JAD 5 (3) JAD I and (4) JAD6 The legends are Ra-226(T) Pb-214 (•I. Bi-2I4(«) A K. Mahur et al I NucI Insir and Meth m Phys Re\ B 266 (2008) 1591-1597 1595 gram size) sample (100 g) was placed at the base of the Ra«, = Cu + 1 43Cn + 0 07CK (5) Can. The Cans were sealed for 100 days Thus the lower It has been assumed here that 370Bqkg"' ^''U or sensitive part of the detector is exposed freely to the emer 259 Bq kg"' ^"Th or 4810 Bq kg"' "^K produce the same gent radon from the sample in the Can so that it could gamma dose rate record the tracks of alpha particles resulting from the decay Ra^ is related to the external y-dose and internal dose of radon in the remaining volume of the Can and from due to radon and its daughters ^"Po deposited on the inner walls of the Can Radon Beretka and Mathew [6] defined two other indices that and Its daughters reach equilibrium in about four hours represent external and internal radiation hazards The and hence the equihbnum activity of emergent radon can external hazard index is obtained from Ra^q expression be obtained from the geometry of the Can and the time through the supposition that its allowed maximum value of exposure After the exposure the detectors were etched (equal to unity) corresponds to the upper limit of Ra^q in 2 5 N NaOH at 60 ± 1 "C for a period of 90 mm m con (370Bqkg"'') The external hazard index {H„) can then stant temperature water bath for revelation of tracks The be defined as resulting ot-particle tracks were counted using an optical microscope (magnification 400X) The activity was //« = Cu/370 + CTh/259 + CK/48 10 ^ 1 (6) obtained from the track density in the etched detectors This index value must be less than unity in order to keep using the calibration factor of 0 056 track the radiation hazard to be insignificant cm~^ d"'(Bq m~^)~' obtained from our earlier calibration experiment [2,18]. The exhalation rate of radon is obtained 4. Results and discussion from the expression [17,19,20]: CV> Uranium has a heterogeneous distribution in earth due Ex = (2) A[T + i(e-^T-l}]' to geochemical processes which have slowly recycled the crustal material to and from the earth's mantle It is found where Ex is the radon exhalation rate (Bq m"^ h"'), C the with widely varying concentrations m different types of integrated radon exposure as measured by LR-115 type 11 rocks The uranium activity is widely distributed/dispersed plastic track detector (Bq m"' h), Kthe effective volume of in a heterogeneous media like the Singhbhum shear zone Can, A the decay constant for radon (h~'), Tthe exposure The radioactivity (primarily uranium) can be observed in time (h) and A the area covered by the Can (m^) the entire zone However significant mineralization is restricted to a few places and suitable locations m compat J 3 Estimation of dose rate ible host rocks [24]. Earlier measurements undertaken by us supports this contention [3,13]. Fig 2 shows typical Outdoor air absorbed dose rate D in nGy h~'due to ter gamma spectra of Jaduguda uranium mine samples JAD restrial gamma rays at 1 m above the ground can be com- 2, JAD 5, JAD 1 and JAD 6 If shows a wide variation in the natural radionuclide concentrations as evident by puute d from the specific activities, Cy Cjh and CK of U/^2*Ra, "^Th and "^K. inBqkg"', respectively by the characteristic peaks Table I presents the values of spe cific activities of "*U, "^Th and *'K together with their Monte Carlo method [2I](UNSCEAR, 2000) corresponding total uncertainties The results indicate D (nGy h"') = 0 462Ci, + 0 604CTh + 0 0417CK (3) reasonably high radioactivity from 123 ±7 to 40,858 ± 174Bqkg"' for uranium with almost no Th which is To estimate the annual effective dose rates, the conver expected in uraniferous regions Only two samples showed sion coefficient from absorbed dose in air to effective dose, potassium activity of l62±llBqkg"' and 9024± 0 7 Sv Gy"' and outdoor occupancy factor of 0 2 proposed 189 Bq kg"' The variations of natural radioactivity levels by UNSCEAR, 2000 [21 ] were used The effective dose rate at different sampling sites are due to the variation of in units of mSvy"' was calculated by the following concentrations of these elements in geological formations formula Tabic 1 Effective dose rate (mSv y ') Average atliviiy u>ncenlration of uranium thorium and potassium of = Dose rate (nGy h ') x 8760 h x 0 2 roik s,imples as well as the corresponding standard deviation Sample Activity concentration (Bqkg ') x07SvGy'' X 10" (4) -'•u ='-Th "K The distribution of ''*U/"*Rd, "-Th and ""'K in rock JAD 1 ^970 ± 65 BDL BDL samples is not uniform Uniformity with respect to expo JAD 2 40858 ± 174 BDL BDL JAD1 9577 ± 95 06 BDL 9024 ± 189 sure to radiation can be defined in term of radium equiva JAD 4 18297 ± 116 BDL BDL lent activity (Racq) in Bq kg ' to compare the specihc JAD <; 10861 ± 106 BDL BDL activity of mdterid\s containing different dmounts of JAD 6 ^0^S6 ± 178 BDL BDL 226, Ra, ^'^Th and ""K U can be calculated from the foUow- JAD 7 121 ±7 BDL 162 ± 11 ing relation [22,23]: *BDL below detection limit 1596 A K Mahur et at I NucI Instr and Meth m Phys Res B 266 (200S) 1591-1597 Values of radon activities and radon exhalation rates from Table 3 the rock samples measured using the "Sealed Can tech Radon exhalation rate in rock samples from Jaduguda uranium mines in nique" are given in Table 3 Radon activities are found Smghbhum shear zone Jharkhand to vary from 11,687 1 ± 128 5 to 38,061 4 ± 232 2 Bq m"' Sample Track density Radon activity Radon exhalation whereas the radon exhalation rate vanes from 4 2 ± 0 05 (cm"-d-') (Bqm ^) rate(Bqm"^h~') to 13 7 ± 0 08 Bq m"^ h"' There is positive correlation JAD 1 16658± 1! 5 29746 5 ± 205 3 107±007 between U-concentration and radon exhalation rate The JAD2 2I3I4± 130 38061 4 ±232 2 137±008 JADl 1752 5 ± II 7 312949±2097 11 3 ± 0 08 high radon exhalation rate m the range of ~4 2- JAD 4 1877 1± 12 2 33466 3 ±217 5 120±08 13 7 Bq m~^ h"' are in broad agreement with our previous JAD 5 1837 1± 12 1 32806 0 ±216 5 11 8 ± 0 07 preliminary studies from Jaduguda U-mines [2] and is JAD 6 2015 9 ± 12 7 35994 9 ± 226 7 129 ±008 expected due to the presence of uranium m highly weath JAD 7 655 2 ± 7 2 11687 1 ±128 5 42±005 ered schist and apatite magnetite rocks Ground water Average 1705±ll 5 30436 7 ± 205 2 109±007 flow, solution movement and the presence of folds and SD 452 2 ± 1 8 8076 3 ± 32 5 29±001 fractures in them may further enhance the emanation Re! Std (%) 26 52 ±15 7 26 53± 15 8 26 60 ± 14 1 Radon exhalation rates strongly depends on the parameter like (i) uranium content (ii) presence of enriched soil or rock and (in) the permeability, moisture content, relative humidity and associated meteorological parameters In Table 4, a comparison of radiometric and radiologi Although radon levels tend to be very high m the con cal data has been presented with those computed from fined spaces of underground drifts, elevated radon levels the radiometric data obtained from our earlier measure are also found in open pit mines and around U-mill tail ments [2,3,25] carried out on the geological samples from ings From open pit mines the radioactive emissions are different mineralization zones in Singhbhum shear Zone radioactive fugitive dust and radon gas The concentration of uranium in the different rock samples From the values of Cy C-m and CR. it is possible to eval from the copper and uranium mines in the shear zone uate the annual eflective dose due to y-rays at 1 m above (Table 4) exhibits uneven distribution of uranium A signif the ground Annual effective dose rates are estimated using icant non uniformity is exhibited by the samples from simple calculations considering indoor occupancy factor of Jaduguda The average uranium concentration and radon 0 8, proposed by UNSCEAR report (1993, 2000) [7,21] exhalation rate are highest in Jaduguda U mines At Rakha which implies that 20% of the day is spent out doors, on and Pathargora both Cu and U mineralization occur while an average around the world Bhatin is enriched in uranium with the absence of Cu Table 2 summarizes the values of absorbed dose, annual Jaduguda region has high grade uranium ores Absorbed effective dose, radium equivalent activity and external haz dose rate vanes from 233 0 to 7054 2 nGy h~', Jaduguda ard index Absorbed dose rates vary from 63 6 to U-mme samples having the highest value Bhatin Cu-mines 18876 4 nGyh"' with an average value 7054 2nGyh"' give also higher values as these are nearer to Jaduguda U- The annual external effective dose rates vary from 0 7 to mmes At Surda U and Cu mineralization are closely asso 23 2mSvy"', with an average value of 8 8mSvy~' ciated though not always coincident The calculated values Radium equivalent activity (Rac^) ranges from 134 3 to of //ex for the rock samples range from 1 4 to 41 2 As all 40,858 0 Bq kg"' with an average value of 15,245 3 Bq kg~' these values are higher than unity, the region is not safe and the calculated values of external index hazard (//«,) and may pose significant radiological threat to the vary from 0 36 (o 110 4 with an average value of 41 2 population Table 2 Absorbed dose rale annual enixlive dose Ra,, atlivity and external hazard index in rock samples from Jaduguda uranium mines in Singhbhum shear zone Jharkhand No Sam pie Absorbed dose Annual cflci,livc dose Radium tquivaknt External hazard rate (nOy h"') (mSvy ') attivily (Ra^) ( Bq kg ') index (We,) JAD 1 2758 1 14 5970 0 16 1 JAD 2 18876 4 212 408^8 0 1104 JAD ^ 4791 6 59 10208 7 27 7 JAD 4 84512 104 18297 0 49 5 JAD 5 5018 7 62 108610 29 4 JAD 6 9418 ^ 11 6 20186 0 5-; 1 JAD 7 616 07 114 1 04 Average Vrfluc 7054 2 88 1524>1 41 2 bD 5655 6 6 8 I22M 5 11 1 Rel Sid ('/,) 80 2 77 2 80 4 80 1 A K Mahur et al I NucI Instr and Melh m Phys Re^ B 266 (2008) 1591-1597 1597 Table 4 Radjuin equivalent activity, absorbed dose rate, external hazard index and effective dose rate in rock samples from different mine regions in Singhbhum shear zone Places Radium equivalent Absorbed dose External Effective dose activity (Bq kg"') rateinGyh'') hazard index rate(mSvy~') Mosbani mines (Cu-U mines) 524 7 233 0 14 0 28 Pathargora mines (Cu mines) 919 7 428 8 24 0 52 Bhatin mines (Cu-U mines) 5'?n I 31554 14 9 3 86 Badia (Cu-U mine) 522 9 262 6 1 5 0 32 Rakha mines (Cu-U mines) 892 77 415 7 24 0 50 Surda mines (Cu mines) 1905 2 880 7 52 108 Jaduguda (U-mines Present study) 15245 •? 7054 2 41 2 8 80 5. Conclusion [5] R Anjos, R Veiga, T Soares. A Santos, J Aguiar, M Frascac, J Brage, D Uzeda, L Mangia, A Facure, B Mosquera, C Carvalho, High values of uranium and radon exhalation rates in P Comes. Radial Meas 39 (2005) 245 [6] J Bcietka, P Mathew, Health Phys 48 (1985) 87 the rock samples from different parts collected from Jadug [7] UNSCEAR. United Nations Scientific Committee on the Effects of uda U-mJnes of the Singhbhum shear zone have been Atomic Radiation. Source and Effects of Ionizing Radiation. United found and are characterized by their higher concentration Nations, New York, 1993 of uranium A positive correlation has been found between [8] A M El-Arabi. Radiat Meas 42 (2007) 94 the radon exhalation rate and uranium concentration i9]JH Lubin, D BoiceJr.J Natl Cancer Inst 89(1997)49 [10] A P Radhaknshna, H M Somashekarappa. Y Narayna. K Sidd- There is heterogeneous distribution of U which is very appa. Health Phys 65 (1993) 390 common in crustal rocks Computed radiological data indi [ll]RI Rudnic. S Gao. Composition of the Continental Crust, Treatise cates that the region is not safe and may pose significant on Geochemistry. Vol 3, Elsevier, Amsterdam, 2003, p 1 radiological threat to the population [12] K K Sinha. A K Das. R M Sinha. L D Upadhayay P Pandey V L Shah, Explor Res Atomic Mine 3 (1990) 27 [13] D Sengupta, S Mitra, SK Palnaik, A R Ghosh. Indian J Geo 68 Acknowledgments (1996)20 [14] KL Bhola. Proc Indian Natl Sci Acad 37A (1971) 277 The authors wish to thank. Chairman, Department of Ap [15] A Kumar. K S Narayani, D N Sharma. MC Abani. R.idiat Prot plied Physics, Ahgarh Mushm Umversity, Ahgarh for provid Environ 24 (I&2) (2001) 195 ing the facilities for this work Sincere thanks are also due to [16] R B Firestone. V S Shirely. Table of Isotopes, eighth ed . John Wiley and Sons Inc , New York, 1998 Dr Amit Roy, Director Inter-University Accelerator Centre, [17] A J Khan, R Prasad, RK Tyagi. NucI Track Radial Meas 20 New Delhi for providing HPGe spectrometry system for the (1992)609 analysis of natural radionuclides and constant encourage [18] A K Singh. P J Jojo, A J Khan. R Prasad, T V Ramchandran ment Prof Rajendra Prasad wishes to thank. All India Radiat Prot Environ 20(1997) 129 Council of Technical Education, Government of India for [19] RL Fleischer, A Morgo-Campero. Geophys Res 83(1978)3539 providmg Emeritus Fellowship to carry out this work Fman- [20] R Kumar, A K Mahur. D Sengupta. R Prasad. Radiat Meas 40 (2005) 638 cial assistance provided by Department of Science and Tech [21] UNSCEAR. United Nations Scientific Committee on the Effects of nology (DST), Government of India to Dr Rajesh Kumar as Atomic Radiation. Source and Effects of Ionizing Radiation, United Young Scientist under Fast Track Scheme (Award No SR/ Nations. New York. 2000 FTP/PS-31/2004) IS gratefuUy acknowledged [22] KN Yu. Z Guan. M J Stoks EC Young. J Environ Radioact 17 (1992)31 [23] V Kumar. TV Ramchandran. R Pr.is.id. AppI R.idial Isot 51 References (1999)93 [24] S C Sarkar, Geology and ore mineralisation of the singhbhum [I] EC, European commission report on radiologiuil protCLlion princi copper-uranium beH. Eastern India. Jadavpur University Calcutta ples concerning the natural radioactivity of building materials 1984. printed at IN A Press, Cateutta 700 032, distributed by Radiat Prot (1999) 112 Granlhlok Jadavpur University. Calcutta 700 032 [2]AK Singh. D Sengupta, R Prasad AppI Radiat Isot 51 (1999) [25] D Sengupta, R, Prasad Radiometric and radon exhalation studies 107 along Cu-U deposits, in Singhbhum Shear Zone Jharkhand [3] R Kumar. D Sengupta, R Prasad, Radiat Meas 36 (2003) 551 Environmental Implications National Seminar on Mineral Based [4] N K Ahmed, A Abbady. A M El Arabi. R Michel A H El- Industries Proteedings, 2001 p 187 Kamel AG Abbady Indian J Pure AppI Phys 44(2006)209 Available online at www.sciencedirect.com *%' ScienceDirect RsdteUM MMtwmMits ELSEVIER Radianon Measurements 43 (2008) S520-S522 www elsevier com/locate/radmeas Measurement of effective radium content of sand samples collected from Chhatrapur beach, Orissa, India using track etch technique A.K. Mahur, M. Shakir Khan, A.H. Naqvi, Rajendra Prasad, Ameer Azam* Department of Applied Physics, Z.H College cf Engineering and Technology, Aligarh Muslim University, Aligarh 202002, India Abstract Track etch technique using LR-115 plastic track detectors has been used to measure the effective radium content of sand samples collected from Chhatrapur beach of Onssa state (India). The values of effective radium content have been found to vary from 63.6 to 773 5Bqkg~ withm about ±15% The values for 13 samples were found below and values for 7 samples were found above the linut of 370Bqkg~' recommended for the safe use of building matenals for dwelhngs by Orgamzation for Economic Co-operation and Development (OECD) © 2008 Elsevier Ltd. All rights reserved. Keywords Radium content. Track etch techmque, LR-115, Chhatrapur beach 1. Introductioii Orissa, on the southeastern coast of India. This area extends over a length of 20 km, trending NS-SW with an average width Radium is one of the radionuclide of concern. This mainly of more than 1.5 km (Mohanty et al., 2004). enters the body in food and tends to follow calcium in metabolic processes to become concentrated in bones. The radiation given 2. Experimental and theoretical details off by radium bombards the bone marrow and destroys tissue that produces red blood cells. It also can cause bone cancer. The sand samples were collected from the Chhatrapur beach Radium is chemically similar to calcium and is absorbed from placer deposit by the grab sampling method. The study area soil by plants and passed up the food chain to humans. The is extended over a length of 20 km trending NE-SW with an radium content of a sample also contributes to the level of en average width of more than 1.5 km. The experimental setup is vironmental radon as radon is produced from ^•^Ra through shown in Fig. 1. Dried sample (100 g) was placed at the bottom alpha decay. Sand is used as a construction material in build of the plastic can. The mouth of the can was sealed with a ings. Higher values of ^^Ra in sand contribute significantly in cover fixed with LR-115 type n plastic track detector in such a the enhancement of indoor radon in a dwelling. By knowing way that the sensitive surface of the detector faced the sample. the radium content of a sample we can predicate if it can be The detector records the tracks of alpha particles emitted by used as a constructive material. In the present study track etch radon gas produced through the alpha decay of radium. The technique using LR-115 plastic track detectors has been used track density p (in track m~^) is related to the radon activity to measure the effective radium content of sand samples col concentraticm CRD (in Bq m~^) and the exposure time T by the lected from Chhatrapur beach of Orissa state (India) and some formula (Somogyi et al., 1986) samples collected from rivers. The Chhatrapur beach placer deposit (84°54"2'-85°N lat.; p=KC^T (1) 19°15"-19°26"36'E Long.) is located in Ganjam district. where K is the sensitivity factor of LR-115 track detector. The value of K for a can of radius 3.5 cm and height 10cm * Corresponding author Tel +919412808481 is ^ tracks cm~-^d~' (Bqm~^)~' with an uncertainty of 15% E-mail addresses ajaymahur34S@redimail com (A K Mahur), (Somogyi, 1986). It is necessary that for this value of K, the azani222@rediffinail com (A Azam) etching is carried out to reduce the thickness of the LR-115 type 1350-4487/$-see front matter © 2008 Elsevier Ltd All nghts reserved doi 10 1016/j radmeas 2008 04 OS 1 A K Mahur et al. / Radiation Measurements 43 (2008) S520-S522 S521 Sealed. 3. Results and discussion Cover LR-llSType \ 11 Plastic Track Table 1 depicts the values of effective radium content of Detector sand samples collected from Chhatrapur beach, Orissa, India. It is seen that values of effective radium varies from 63.6 to • Sensitive Surface 773.5Bqkg"' with an average value of 319.0Bqkg"'. These values are lower than the values found for Brazilian beach sand (Veiga et al., 2006). Table 1 also presents the value of effective 7 cm radium content of sand samples collected from different rivers. • Plastic Can It shows that the value of effective radium content varies frt)m 10 cm 17.3 to 29.5Bqkg"' with an average value of 21.6Bqkg"'. RADON GAS Average ^*U concentration in the sand samples from Chha trapur beach is 220Bqkg"' whereas ^^^Th concentration is 2500Bqkg"'(Mohanty et al., 2004). The concentration of ^^Rn is expected to be small due to its very small half life Sand Sample and subsequent low exhalation rate. 'A.'AT.v.r.gg.trA.g.ttr.y.vjiiiif Jf A tmmif AVJAVi. 1 It is clear fromTabl e 1 that the values of effective radium con tent in sand samples collected from Chhatrapur beach are higher Fig. 1. Experimental setup for measurement of radium content in sand samples than the values of effective radium content of sand samples col lected from rivers. The higher values in the beach sand samples detector to about 5 nm (Somogyi, 1986), which is obtained by may be attributed to the presence of radiogenic heavy-minerals 2 h etching of the detector in 2.5 N, NaOH solution at 60 °C in in these samples. The heavy mineral assemblage includes il- a constant temperature water bath to reveal the tracks. Alpha menite, garnet, sillimanite, rutile, zircon monazite, magnetite tracks were counted by an optical microscope at a magnification Table 1 of 400 X. The minimum (range of alpha particle) track diameter, Effective radium content m different sand samples counted was 11 ^m. S no Source of sample Effective radium content Since the half life of ^^^Ra is 1620 years and that of ^^^Rn with code is 3.82 days, it is reasonable to assume that an effective equi CRa (Bqkg-') librium (about 98%) for radium-radon members of the decay series is reached in about 3 weeks time. Once the radioactive Samples fmm beach 1 Beach (B-7) 63 6 equilibrium is established, one may use the radon alpha analy 2 Beach (B-4) 68 8 sis for the determination of steady-state activity concentration 3 Beach (B-20) 98 4 of radium. Hie activity concentration of radon begins to in 4 Beach (B-14) 106 1 crease with time T, after the closing of the can, according to 5 Beach (B-9) 108 7 the relation 6 Beach (B-2) 1101 7 Beach (B-8) 114 6 CRn = CRad - e-^'*"'') (2) 8 Beach (B-10) 132 7 9 Beach (B-3) 158 7 where CRa is the effective radium content of the sample. Since 10 Beach (B-6) 183 4 a plastic track detector measures the time-integrated value of 11 Beach (B-17) 238 8 12 Beach (B-1) 305 3 the above expression, i.e. the total number of alpha disintegra 13 Beach (B-19) 3179 tions in unit volume of the can with a sensitivity K during the 14 Beach (B-U) 389 8 exposure time T, hence the track density observed is given by 15 Beach (B-16) 557 0 16 Beach (B-5) 587 9 p = ATCRaTe (3) 17 Beach (B-13) 652.2 18 Beach (B-18) 654 6 where Te denotes the effective exposure time given by 19 Beach (B-12) 758 3 20 Beach (B-15) 773 5 n = iT-x-hi -iRnT" )J (4) Average value 3190 SD 250 7 In these measurements the exposure time T is 150 days. Rel std.% 78 6 Finally, the "effective radium content" of a specimen in a Samples fmm river can (see Fig. 1) can be calculated by the formula 1 River (R-l) 17 3 2 River (R-2) 184 CRa(Bqkg-') (5) 3 River (R-3) 213 \KTJ\M) 4 River (R-4) 29 5 where M is the mass of the solid sample in kg, A is the area Average value 216 SD 55 of cross-section of the can in m^; /i is the distance between the Rel std% 255 detector and top of the solid sample in m. S522 A.K. Mahur et al. I Radiation Measurements 43 (2008) S520-S522 and minor amounts of hornblende, diopside, sphene, tourma References line, epidote and pyroxene, while the light sand minerals are quartz, feldspars and some mica. The ilmenite, garnet, silliman- Mohanty, A.K., Das, S.K., Van, K.V., Sengupta, D., Saha, S.K., 2003. ite, rutile, zircon and monazites are present in the samples in Radiogenic heavy minerals in Chhatrapur beach placer deposit of Orissa, decreasing order of abundance (Mohanty et al., 2003). It is also Southeastern coast of India. I. Radioanal. Nucl. Chem. 258 (2), 383-389. Mohanty, A.K., Sengupta, D., Das, S.K., Saha, S.K., Van, K.V., 2004. clear from the table that 13 samples have effective radium con Natural radioactivity and radiation exposure in the high background area tent below 370Bqkg~' and 7 samples have effective radium at Chhatarpur beach placer deposit of Orissa, India. J. Environ. RadioacL content above 370Bqkg~'. The samples having effective ra 75, 15-33. dium content greater than 370 Bq kg~' are not advisable to be OECD, 1979. Organization tor economic cooperation and development used in construction of dwellings as it is the limit for overall exposure to radiation from natural radioactivity in building materials. radium content as recommended by OECD (1979) for the safe Report by a group of experts of the OECD Nuclear Energy Agency, OECD, Paris. use of building materials for dwellings. Veiga, R., Sanches, N., Anjos, R.M., Macario, K., Bastos, J., Iguatemy, M., Aguiar, J.G., Santos, A.M.A., Mosquera, B., Carvalho, C, Baptista, Acknowledgements Filho, M., Umisedo, N.K., 2006. Measurement of natural radioactivity in Brazilian beach sands. RadiaL Meas. 41, 189-196. Somogyi, G., 1986. Track detection methods of radium measurements. The authors are thankfiil to Prof. D. Sengupta, Indian In ATOMKI Preprint E/25. stitute Technology, Kharagpur and Dr. Masroor Alam, Aligarh Somogyi, G., Hafez Abdel-Fattah. Hunyadi, I., Toth-Szilagyi, 1986. Muslim University, Aligaifa for providing the sand samples and Measurement of exhalation and diffusion parameters of radon in solids by fruitful discussion. plastic track detectors. Nucl. Tracks 12, 701-704. AmiabiB onine at www.science(irectoom '%' SdenceDirect ELSEVIER i43(20a8)SSa8-SSll www.ebeviaxaniAocaK/raihnBas Radon exhalation ratefro m sand samples finomth e newly discovered high background radiation area at Erasama beach placer deposit of Orissa, India RajeshKnmar*-*, A.K.Mahi]r', N. Sulekha Rao^ D.SenglIpta^ Rajendra Prasad' ^Depmtmem of Geology tmd Gtopkyaa, IJ.T, aiamgfrv-7213tB, India AMnct iKBuki teffOB wiricfa in due to ihe preaence of radioeeaicheav y mmeiih. The sjnd amplfes coBWinine heivy mmenjs were critected fiwwn EcHiaa beach plMcr dqnck I7 Ihe gnb noqding nelhad fiom pteoes «t n iniennl of ~ Itan. Radoa HriMtartw tmti were iiie«uiBd by "XlmT twhuMfif Dsmg LR-115 type II plastic tnck detector to estimle the ladiatioB caqxMore in givea imneyhere. Radm activily is fimid tomyfion I47I ±46 to 4686±87Bqm~^ widi aa avenge vatae of 3349 ±68Bqin~^ whereas die ladan exfaafaiiaa nie varies fiam S29± 1610 168S±31iiiBqiii~^ h~' widi an avenge vahie of 1204±25inBqm~^ h~'. Ynation of ladon caduladon me widi die 1 rur. Thf «pliip« nl*»iiinH »»> ini taffwr gifc anH may piwe a radiatinn riA In amhiw* i-Mwiimiiiif-nt, if die ««J is iMed «» mmdmilWiii miiBfial O 2008 Elsevier L^ Anri^as reserved. Jtqwwiii. Radoa r aadk deleclan; Scded Cia 1. Introduction Macdonald et aL, 1997; Aly Abdo et aL, 1999). DislribDiian of naturally occurring radionuclides mainly ^^U, ^^Th and *'K Naturally occurring radionuclides of terrestrial origin are and other radioactive elements in solids depends on the distri- present in the earth's crust since its origin. Radioactive toxic ele buticm in rocks from which they originate and on the processes ments uranium, thorium and potassium are found in traces in al through which they are concentrated. Higher concentrations of most all types of rock, sand, soil and water. DIK to its property to radionuclides such as ^*U, ^^Th and *'K occur in minerals get dissolved in aqueous solution in hexavalent (U^) from and such as monazites and zircons. High background radiation to precipitate as a discrete mineral in tetravalent (U^'*') form, areas (HBRAs) are found in the world and are due the local ge uranium forms deposit in the earth's crust where die geologi ological controls and geochemical effects and cause enhanced cal conditions become favorable. Human beings are exposed to levels of tenestnal ndialkn (UNSCEAR, 1993, 2000). IWde ionizing radiation from natural sources due to flie occurrence ranging radiation studies have been carried out in the HBRAs of natural radioactive elements in solids: rocks, sand, soil, etc; in Bnzfl(FlBnna Franca, 1977; Bennett, 1997; Pssdioa, 2000). cosmic rays entering the eartii's atmosphere from outer space in China (Wd et aL, 1993; Wd and Sugahara, 2000), in India and the internal exposure from radioactive elements through (Snnta et aL. 1982; Santa, 1993; Mishra, 1993; PIBOI et aL, food, water and air. Natural radioactivity is wide sfHead in the 1998). in Iran (Sohiabi, 1998; Ghiassi-nejad et al., 2002X in earth's enviroimient and it exists in various geological fomiia- USA and Canada (NCRP, 1987) and in some odier comlnes tions in soil, rods, water, sand and air (UNSCEAR, 1993; (UNSCEAR, 2000) to estimate risks and efiEects ofkng-lcnn radiation exposure. * CkMiBpniii« aahot "UL: 49157! 2743X37; bx: -1919410643341. In India there exists some natural HBRAs due to monazite E-mail atUiat: diniaMM9i«fiffiiiiiLcaiii Ot- Kma). sand bearing placer deposits along its long coast line in south 13Sa44S7n-Ke trot mmcr O 2008 Efaevicr Lid. AD n^at lacrnd. dofciaioias jriMw 7niiK.04.ow croL/ 43 (2aOS) SS0g~S5Il SS09 India sudi as UDd in Kamalak (Raiftakrishna et aL, 1993X retrieved and were eldied in 23N NaOH tt 60 ± 1 °C far Kalpakkam in Tannlnadn (Kannan et al., 2002), coastal ports a period of 90min in a constant temperature water badi for of Tamilnadu and Kerala and the soudiwestem coast of In revdation ci tracks. Resulting aJ^te trads on the eaqiosed dia (Mishra, 1993; Sunta, 1993). Recendy Mohanty et al. face of the detector foils woe scanned under an optical mi- (2004a, b) haw cacdcd out nalnni rafioKtinty measmonenls amnxye at a m^mficadon of 400x. The calibniion hdar in the newly discovered HBRA on the eastern coast of Orissa, cf 0.0S6Trcm~^ d~' obtained fiom an eariier caHbmian ex and higher levels of uranium, thorium and potassium are periment for LR-llS qrpe-n detector (Singb et aL, 1997) was observed in the sand samples. used to compute the radon activity from the track density. Radon, an x-radioactive inert gas indicates the presence of Fdkiwing oqaessian gives die cxiHiatian nMe (Fldsdier aid radium and its ultimate precursor uranium in the ground. Ura Moigo-campao, 1978; Khan et al., 1992; Kumar et al., 20QS): nium has heterogeneous distribution in earth and is found to CVi. have wide variation in its ccmcentratirai. As an inert gas and hav Ex = (1) ing sufficiendy large lifetime can move freely through the ma AlT + l/l{e -iT _ 1)1 terials like soil, sand, rock, etc. Short lived daughters of radon where Ex is die radon exhaladoa rale in Bqm~^h~', C is are eslddiaiied as caosHivc ageals of tangcaocc r (UNSCEAR, the integrated radonexposur e as measured by LR-llS type n 1993, 2000). Under spedBc condilians sodi as pnivailing in plastic tradk detector in Bqm'^h, V Is die dfedive volume of the uranium mining environment and in HBRA's the lung dose Cm in m^, 1 is die dec^ constant for radon in h~', T is die dne to ladon pwigenics mqr be snffidendy bigb (Kmnar et aL, exposuie time in hand A Is the area cowered by the Ci in m^. 2003). Radon exhaling properties of porous materials sne of prime ixaponaace for the estimation of radiation risk and have beca die snbiect of several invcstigMians (Jooassen, 1983; Kanmdoost et aL, 1988; Kumar et al., 2003, 200S, 2006; The sand is die basic ingredient used in constiuctian ma Mafanr et aL, 20QS). The condadon between die mninm terials in India. By mixing it widi cement, sand is cammanly ccmcentraticm and the radcn emanation potential of the source used as a binding material for fired clay and fly adi bri(±s for material is required for radcm risk. In the present study radon the constiuctian of waDs and also as a plasleriitg mafcriaL ft is exhalation rate measurement from the sand samples of the also used in die prqparalion of concrete. Thus, it is quite impor Erasma beach placer deposit, a part of the eastem coast of state tant to find its radonemanatio n potential to have an estimaixm of Orissa, India, has been carried out for finding its correlation of raifiatianridi to die habitants. The values of radonactivi ^ with uranium concentration. and radon exhaladion rates in the sand saiii|4es are presented in Table 1. U-coooenlntion in dieae sani|4es as mtasuml by our 2. Experimental method 13Mel Can technique was used for the radon exhalation measure ments. This is supposed to be the most efBcient method for Savie Trade Radoa adhi^ Radoa edobliaa U^n the measurement of time integrated radon exhalation rate. The mate deaaqr (fiqwr^) mc (Bqa-^ h-') sample is placed in the lows' part of a sealed cylindrical can Cn-o and an a-sensitive solid state nuclear track detector is fixedo n ERl 114.6 ±3.0 2046 ±54 736±19 16L2 diBinneruppersuifooeafdiecan(Abo-JaradetaL, 1980; Khan ma 2Z2j6±4.2 3974i:7S 1429±27 32.4 el al., 1992; Kumar et al., 2003). In sudi measurements, it is ER3 ll6J±3i)2lOO±SS 755±20 20.2 expected that the exhalation ratedepend s upon the material and ER4 2Z7.S ±43 4069 ±76 1463±27 36L4 its amount as well as on the geometry and dimension of the Can ERS 228Jt±4.4 4a86±79 1469±28 36.4 and can be estimated widi snffident accuracy (Sooiogy et al., Elt6 8Z.4±2.6 1471 ±46 529±16 12.1 ER? IIS.2±3.O20S7±S4 739±19 16.2 1986). Sand samples odlected from die Erasama beadi |riaoer ERS 243.2 ± 4.4 «43± 79 1561 ±28 40L5 deposit of Orissa, India were dried and sieved through a ER9 224J)±4.2 4000±7S 1438 ±27 32.4 100-mesh sieve. Equal amount of each sample (100 gm) ERIO 246L4±4.4 44a0±79 15S2±28 405 was placed in the Cans (diameter 7.0 cm and height 7.5 cm) ERll 134.4 ±33 2400 ±58 863±21 243 siimlar to diose used in die caHxation expeiiuient (Singh ERI2 2S6.6±4.S4SS3±S1 1648±29 403 ER13 256.0 ±43 4571 ±80 1643 ±29 403 et aL, 1997). In eadi On a LR-1 IS Qrpe-n itetic track detec ERI4 136J)±33 2«29±S9 S73±21 243 tor (2 cm X 2 cm) was fixed at the top inside of the Can. The ERIS 118.4 ±3.1 2114 ±55 760±20 20L2 sensitive lower surface of the detector is thus freely exposed ERI6 114.4 ±3J0 2043 ±54 734±I9 162 to the emergent radon from the material in the Can so that it ER17 211.2±4.13771±73 1354±26 283 is ci^Ktble of recording the alpha particles resulting from the ERIS 232J)±43 4143±77 1489±28 36.4 decay of radon in the Can. Radon and its daughters reach an ER19 123.2 ±3.1 2200 ±56 791 ±20 20L2 ER20 22S.0±43 4071±76 1464±27 32.4 equilibrium concentration after a week or more and thus the ER21 120J)±3.12143±55 770±20 2012 equilibrium activity of emergent radon could be obtained from ER22 225.6 ±4:2 4029 ±76 1448±27 32.4 the time of exposure and the geometry of the Can. After the ER23 260L0±4.64643±S1 1669±29 403 exposure for 1{X) days, the detectors from all tiie Cans were ER24 262.4 ±4.9 4686 ±87 1685 ±31 36.4 SSIO Jt. Kmmir et aL / KaJiadam Meaammaia 43 (2008) SS0g-S5II -abk2 ture and grain size cancemralian. To investigate the condalian f IIMIIIW rale in ififluuol *™*'^^ between die radon exhalation rate and tbe uranium conoentra- S.MI. S-pfc tion in die samites, the variation of radon exhalatian nCc with me (•BqB~'h~>) uranimn concentration is {dotted in Fig. 1. K shows a positive 1 173 correlation between the two. 2 6M 3 436 4. Conclusion 4 I«9 5 94 6 63 Radon exhalation rates from the sand samples from Erasama 7 40 beach placer deposit, a newly discovered HBRA of Orissa, In S 2S dia, studied here have much higher values than the sand sam 9 S2 ples from nonnal background region and also fit)m other build 10 13 ing materials used in India. As the sand is the basic ingredient 11 108 12 1203 used in construction materials in India, the use of sand from this region as construction material may give significant radia tion dose and pose radiological risk to the population. 45 Acknowledgments One of the authors. Prof. Rajendra Prasad, is thankful to All India Council of Technical Education, Government of India for providing Emeritus Fellowship to carry out this work. Finan cial assistance provided by Department of Science and Tech nology (D.S.T.), Government of India to Dr. Rajesh Kumar as Young Scientist (Award No. SR/FTP/PS-31/2004) is gratefully acknowledged. References Abu-Jarad, R, Fremlin, J.H., Bull, R., 1980. A study of radon emitted firom 400 600 800 1000 1200 1400 1600 1800 building nuterials using plastic alpha track detectors. Pbys. Med. Biol. 25 (4), 683-694. Aly Abdo, A.A., Hassan, M.H., Huwait, M.Rj^., 1999. Radioactivity (inBqiir%^) assessment of £d>ricated i^osphogypsum mixtures. In: Fourth Radiation Physics Conference, 15-19 November, Alexandria. Egypt, pp. 632-640. F^ 1. ^ftuMMM of ladoa i Bennett, B.C., 1997. Exposure to natural radiatioo wraldwide. In: Proceedings of tbe Fourtti IntematicMial Confraence oo Higji Levels of Natural Radiation: Radiation Doses and Healdi Efiiects. 19%, Beijing. China£lsevier, Tokyo, pp. 15-23. cirfiabaratafs (Mohanty et al., 2004a) are also givai in Fleischer, R.L., Morgo-campero, A., 1978. Matting and int^iated radon TaUe 1. Radon activilies are found to vanrfian 1471 ±46 to emanation for detection of long distance migration of gasses with in tbe 4686 ± 87 Bq m"^ with an average value of 3349 ± 68 Bq m"^ earth, techniques and principles. Geophys. Res. 83. 3539-3549. Ghiassi-nejad, M., Mortazavi. S.MJ.. Cameron, JR., Niroomand-rad. A., while the radon exhalation rate varies ftom 529 ± 16 to Karam. P.A., 2002. Very high background radiation areas of Ramar. Iran: 1685 ± 31inBqni~^h~' with an average value of 1204 ± preliminary biological studies. Health Phys. 82, 87-93. 25niBqm-2h-i. Jonassen, N., 1983. The determination of radon exhalation rates. Health Phys. It can be observed from the results that the radon exhalation 45. 369-374. rate varies sq^ieciably from one sample to another. In our pre- Kannan. V.. Rajan, M.P., Iyengar. M.A.R.. Ramesh, R., 2002. Distribution of natural and anthropogenic radionuclides in soil and bestch sand sam|des vkns measnrenients (Khan et al., 1992) in some sand sarajdes of Kalpakkam (India) using hyper pure gananium (HPGe) ganmia ray from the nonnal background area of India average radon ex spectrometry. AH>1. Radiat Isot 57, 109-119. halation rate has been found to be 108 mBq m~^ h~'. Present Kannadoost, N.A., Durrani, SA., Fremlin. J.H.. 1988. An investigation of values are much higher than this value and the values (Table 2) radon exhalation from fly ash produced in the combustion of coal. Nucl. for other building materials such as soil, cement, clay bricks, •Racks Radiat Meas. 15. 647-650. Khan, A.J., Prasad. R.. lyagi, R.K.. 1992. Measurement of radon exhalation concrete, marble, fly ash, gypsum, etc. are estimated from our rate from some building materials. Nucl. Tracks Radiat. Meas. 20, eariier studies (Khan et al., 1992; Komar et aL, 20QS). 609-610. It is expected that radon exhalation should depend on the Kumar. R.. Sengupta. D.. Prasad, R., 2003. Natural radioactivity and radon uranium concentration in the samples. But it is worth mention exhalation studies of rock samples fiom Surda Cu deposits in Singhbhum ing that it is difficult to predict the radon exhalation rate from shear zone. Radiat Meas. 36, 551-553. Kumar, R., Mahur, A.K., Sengupta, D., Prasad, R.. 2005. Radon activity and the concentration of uranium or its decay series products in a exhalation rates measurements in fly ash from a thermal power plant sample, since the radon exhalation rate depends also on the tex Radiat. Meas. 40, 638-641. K. Kmmar et aL / Kadbaim Mtaaarmaas 43 (2008) SS08-SSII SSII Kumar, R., Mahur, A.K., Singh, A.K., Prasad, R., 2006. An investigatifm of Radhakiisfana. A.P.. Somasekarapa, HM., Narayana. Y., Siddappa, K., 1993. radon exhalation fi A.K. MAHUR*, FAFESH KUMAR, P.J. JoJo^ ASHAVANI KuMARt. A.K.SiNGHt A.K. VARSHNEYK and RAJENDRA PRASAD Department of Applied Pf^sics, Z.H. College of Engineering and Technology Aligarh Miislin, University, Aligarh-202 002, India E-mail: ajaymahur345@rediffmail. com Radiological importance of radon among other naturally occurring radionuclides is due to the fact xhat it is a noble gas in the uranium decay series with a fliirly long haif-iife of 3.7 days. Being an inert gas it can easily disperse into the atmosphere as soon as It is released. The solid alph? active decay products of radon (^"Po, ^'^Po) become airborne and attach themselves to the dust particles, aerosols and water droplets in the atmosphere. When inhaled, these solid decay products along with air may get deposited in the trachea- bronchial and pulmonar;' region of lungs resulting in the continuous irradiation of the cells, which may cause lung cancer. Measurement of time integrated concentration of indoor radon and its progeny are important as these are responsible for a major part of natural radiation dose to human beings and may be responsible for lung cancer. LR-115 Type II solid state nuclear track detectors hive been used to estimate the radon concentratior in dwellings in various cities from different states of India. Ann-jal effective dose has been calculated from the radon concentration to carry out the assessment of the variability of expected radon exposuie of the population due to radon and its progeny. The radon levels in the dwellings vary from 64.8 to 222.1 Bq m'' whereas annual effective dose vary from 2,5 to 7.5 m Sv. Radon concentration in Panmana (Kerala), the so called high back ground area is about two times 'nore than the normal back ground area. Key Words: Radon, Solid state nuclear track detectors, HERA, Radon activity, Alpha tracks. Effective dose. INTRODUCTION The risk of lung cancer for workers in uranium mines is known for a long time and is related to radon exposure'. Radon is generated from radium present in soil, building materials and even water. Radon is a noble gas in the uranium decay series with a fairly long half-life of 3.8 days. Being an inert gas it can easily disperse into the atmosphere as soon as it is released. The solid alpha active decay products of radon ^2i8pQ 2i4pQ^ become airborne and attach themselves to the dust particles, aerosols and water droplets in the atmosphere. When inhaled, these solid decay products along with air maj' get deposited in the Department of Physics, Fatima Mata National College, Kollam.691 001, India. Department of Physics, SLIET Longowal -148 106, India. Department of Applied Physics, Dronacharya College of Engineering, Gurgaon, India. Department of Physics. G.G.D.S.D. College, Baijnatli-l' 1 125, India. 3372 Mahuretal. AsianJ.Chem. trachea-bronchial.(T-B) and pulmonary (P) region of lungs resulting in the continuous irradiation by a-particles on the cells which may cause lung cancer^"^. Radon in dwellings is generated fiom radium present or existing or accumulated in soil, construction materials and water. Radon and its daughter products may pose a significant health hazard, especially when concentrated in some enclosures such as underground mines, caves, cellars or poorly ventilated and badly designed houses. Thus radon concentration in dwellings is important due to the health risk jjnd to determine the design of control strategies. Indoor radon concentration depends in a complex way on the characteristic of the soil, the type of building structure, ventilation condition and occupant's behavior. In homes the predominant source of radon in indoor air is the soil beneath structures, but building materials and Water used in the homes and in a few cases natural gas may also contribute'. The concentrations of radium in soil and in rocks vary several orders of magnitude. This variation in source strength results in the variation in radon concentrations among dwellings. Keeping the radiation hazards of radon for general population in mind, it is quite important to make a systematic study of the indoor racjon concentration in Indian dwellings. For this purpose, radon measurements have been carried out in a number of dwellings in the cities of different states of India i.e. Mathura, and Agra in U.P; Dehradun in U.A., Banswara in Rajasthan; Palampur and Baijnath in H.P., Bhatinda in Punjab, and Panmana, Eravipuram and Thankassery ia Kerala. Panmana is in the vicinity of the High Back Ground Area (HBRA), whereas Eravipuram and Thankassery are about five to six Km away from HBRA EXPERIMENTAL Nuclear track-e/ch detectors (LR-115 type II Solid Sate Nuclear Detectors (SSNTDs) were employed for measuring the Potential Alpha Energy Concentration (PAEC) of radon progeny in Workin<5 Level (WL) units. The pieces of the detecior films of size 2x2 cm, fixed on a thick flat card were exposed in bare plastic track detection technique • by hanging the cards on the wall in the room for a period of 90 to 100 days such that the detector viewed a hemisphere of radius at least 6.9 cm, the range of ^'*Po a-particles io the air. No surface was closer than this range as the decay products would act as an indeterminate a-particles sources. Detectors were mounted vertical and the locations were so selected that the dust collection on the detectors be minimum. After exposure, the detectors were collected and brought back to the laboratory for analyses. The films were efched in 2.5 N NaOH solution at 60°C for 90 min in a constant temperature water bath. The counting of aloha tracks was done usin^ a binocular oi tical research microscope 3374 Mahure/fl/. Asian J. Chem. TABLE-1 RADON LEVELS AND POTENTIAL ALPHA ACTIVITY IN SOME INDIAN CITIES Potential alpha , " ' !'•. Radon concentration activity (mWl.) Cities No. of Range Aver. Range Aver. S.D. Rel. Std.% dwel. (Bq.m-') value (Bq.m-') , (Bqtri-') Eravipuram 21 2.9- 14.2 26.8- 131.7 56.6 42.9 (Kerala) 17.3 ,227.5 Panmaiia 19 4.6- 24.0 . 42.5 - 222.1 103.0 46.4 (Kerala) 42.5 393.1 Thankasseiy 24 5.3- 17.« 44.3- 144.7 61.5 42.5 (Kerala) 45.4 373.3 Dehradun 34 2.6- 7.9 21.0- 64.8 35.3 54.5 (U.A.) 19.8 162.5 Mathura 39 2.6- VJ..t 20.0- 103.8 45.6 43.8 (U.P.) 22.6 185.4 Agra 36 2.4- 9.7 19.8- 80.3 36.1 44.9 (IJ.P.) 18.4 151.5 Panswara 44 1.8- lis 15.0- 95.9 76.3 79.5 (Rajasthan) 34.4 282.7 Palampur 10 6.9- 15,1 56.7- 123.8 52.1 42.4 (H.P.) 25.8 212.0 Baijnath 15 5.1- 17.ii 41.9- 146.8 72.9 49.7 (H.P.) 32.3 265.5 Bhatinda 33 6.3- 14.9 51.8- 125.6 45.3 36.1 (Punjab) 27.3 224.5 TABLE-2 ANNUAL EFFECTIVE DOSE IN SOME INDIAN CITIES Cities Range Average Value S.D. F.el. Std.% Eravipuram 0.9-7.7 4.5 1.9 42.2 (Kerala) Panmana 1.5-13.3 7.5 3.5 46.7 (Kerala) Thankassery 1.7-14.2 5.5 2.3 41.8 (Kerala) Dehradoon 0.8-6.2 2.5 1.4 54.8 (U.A.) Mathura 0.8-7.1 3.9 1.7 43.9 (U.P.) Agra 0.8-5.8 3.1 1.4 45.2 (U.P.) Banswara 0.6-10.8 3.6 2.9 73.2 (Rajasthan) Palampur 2.1-8.1 4.7 2.0 42.4 (H.P.) Baijnath 1.6-10.0 5.6 2.8 49.8 (H.P.) Bhatinda 2.0-8.6 4.8 1.7 36. i (Punjab) above a continued effective dose of 10 mSv, while an action level within the range of 3-10 mSv per year has been proposed. The action level for radon concentration should be in the range between 200 and 600 Bq m"^ Vol. 18, No. 5 (2006) Radon Levels m Dwellings of Some Indian Cities 3373 with a magnification of 400X. The track density registered in the bare detector will, therefore, be a function of radon and its progeny concentration in air. The radon concentration in Ba.m"^ was estimated from working level by using the following equation*'. R„C(Bqm-') = WLxJTOO F The equilibrium factor for radon has been taken as 0.4 as suggested by UNSEAR, 2000'°. To obtain the Potential Alpha Energy Concentration (PAEC) of radon progeny in mWL, LR-115 type II detector films should be calibrated with a known radon concentration under the conditions almost similar to those, which prevail in Indian dwellings. For this purpose, the detectors were calibrated''''^ in a radon exposure chamber at the facility available in Environmental Assessment Division of Bhabha Atomic Research Centre, Mumbai. The mean calibration factor for LR-115 type II detector was found to be 442 tracks cm'^d"'per WL. RESULTS AND DISCUSSION Table 1 presents the radon levels aiid Potential alpha activity in the dwellings of different cities of various states of India. The radon levels in the dwellings vary from 64.8 to 222.1 Bq m*' and Potential alpha activities vary from 7.9 to 24.0 mWl. The radon activity depends on many factors i.e soil beneath the house, flooring, building materials, ventilation conditions, type of construcrion etc. Panmana in Kerala is the city situated in the vicinity of High Background Area and the radon levels in the dwellings are found to be about two times more than the normo' back ground areas of the state (Eravipuram, the town far from HBRA'"**. The radon activity depends on many factors i.e. soil beneath the house, flooring, building materials, ventilation conditions, type of construclion etc. Palampur and Baijnath cities are siiuated in the hilly region of the state of Himachal Pradesh, a state known for U-mineralization. Radon levels in the dwellings surveyed in thi\se cities are in the action level limit'\ Other cities of the present studies are situated in the normal background areas. Radon levels arc found higher in Mathura as compared to Agra. Both being normal background area, this may be due to Mathura being at closest distance from big oil refinery. Table-2 presents the annual effective dose in the dwellings of different cities of various states of India. The effective dose equivalents using the conversion factor of 9 mSv/WLM proposed by (ICRP 1986)'^ varies from 2.5 to 7.5 m Sv. The International Commission on vladiation Protection (ICRP-65. 1993)'^ has recommended that r6niediaJ action against radon is justified Vol. 18, No. 5 (2006) Radon Lcv.^ls in Dwellings of Some Indian Cities 3375 ACKNOWLEDGEMENTS One of the authors (AKM) wish to thank, Chairman, Department of Applied Physics, Aligarh Muslim University, Aligarh for providing the facilities for this work and also thankful to the residents of the study area for their cooperation during the field work. Prof. Rajendra Prasad wishes to thank, All India Council of Technical Education, Government of India for providing Emeritus Fellowship to carry out this work. Financial assistance provided by Department of Science and Technology (D.S.T.), Government of India to Dr. Rajesh Kumar as Young Scientist (Award No. SR/FTP/PS-31/2004) is gratefully acknowledged REFERENCES 1. J. Sevc, E. Kunz and V. Placek. Health Phys, 54,27 (1976). 2. J.H. Lubin. AmJ. Epidemiol., 140, 323 (1994). 3. J.M. Samet. J. Natl. Cancer Inst., 81,745 (1989). 4. NRC, Health Effects of radon and other internally deposited alpha emitters. Report of the Committee on the Biological EflFects of Ionizing Radiation [BEIR-IV] (1988). 5. V. Nero and W.W. Nazaroof, Radiat. Prot. Dosim., 7,23 (1984). 6. R. Kumar, D. Sengupta and R. Prasad, Radiation Measurements, 36, 521 (2003). 7. H.W. Alter and R.L. Fleischer, HealtkPhys., 40,693 (1981). 8. A.K. Mahur, R. Kumar P.J. Jojo and R. Prasad. Rad. Protect. Environ., 28, 203 (2005). 9. R. Kumar and R. Prassad, Indian J. Environ. Protect., 25, 168 (2005). 10. UNSCEAR, United Nations Scientific Committee on the Effect of Atomic Radiation, Annex A: Exposure from Natural Sources. United Nations, New York (2000) 11. A.K.Singh, A.J. Khan and R. Prasad, Distribution. Radiat. Prot. Dosimetry, 74. 189 (1997). 12. P.J. Jojo, A.J. Khan, R.K. TyagI, T.V. Ramchandran, M.C. Subba Ramu and R. Prasad Radiat. Kttas,, 23, 71S (1994). 13. R. Kumar, A.K. Mahur, A.K. Varshney and R. Prasad, Indian J. Environ. Protect., 24, 588 (2004). 14. ICRP-65, International Commission for Radii^tion Protection; Annals of the ICRP, 23,1, Pergamon Press, Oxford (1993). 15. ICRP, International Commission for Radiation Protection: Protection, New York Publ.No.50(1986). CHEM. ENVIRON. RES. 15 (3 & 4) 2006 287 Study of Indoor Radon Levels in Some Dwellings of Thankassery Town in Kerala A. K. MAHUR", R. KUMAR, P.J. JOJO* AND R. PRASAD Department of Applied Physics, Z. H. College of Engineering & Technology, . Aligarh Mislim University, Aligarh-202002, India "Department of Physics, Fatima Mata National College, Koilam-691 001 India Radon monitoring has become a global phenomenon due to its health hazard effects on popiilation. ^Rn and its radioactive daughters present in the environment results into the largest contribution to the average effective natural radiation dose received by human beings. Indoor ^Rn exposure to the population depends in a complex way on the characteristics of the soil, the building structure, meteorology, ventilation conditions and occupants behaviour. LR-115 type n solid state nuclear track detectors (SSNTDs) have been used for the measurements of indoor radon concentration in 24 rooms of some dwellings situated in Thankassery town along the south west coast of Kerala to carry out the assessment of the variability of expected radiation exposure of the population due to radon and its progeny. The town is situated near the high background area of Kerala. Radon concentrations are found to vary fh)m 44.3 Bqm"' to 373.3 Bqm** with an average of 144.7 ± 61.5 Bqm"' whereas the armual effective dose equivfleiits vary from 1.7 to 14.2 mSv/y with an average of 5.5 ± 2.3 mSv/y. INTRODUCTION In the last few decades, a general social concern about the health risk associated with radon has grown worldwide. Historically, the detrimental effect on health attributed to radon came to light in connection with frequent lung disease (lung cancer) incidences among underground miners. Nowadays attention is paid to radon both at workplaces and homes. Although one usually spends less time at work than at home (the ratio is about 1: 2.5), the radiation e^qposure from radon in the workplace can be significant in cases when the radon concentration is relatively high in work environments. The International Commission on Radiological Protection (ICRP) provides guidance to regulatory authorities on the radon action levels in its publication of ICRP-65 (/). ICRP-65 suggests that workers who are •Author for correspondence : e-mail: ajaymahur345@rediffmaiLcom 288 A.K.MAHURetal. not regarded as being occupational ly exposed to radiation should be treated in the same way as the general public. Public exposure to radon and its radioactive daughters present in the environment results in the largest contribution to the average effective dose received by human beings (2). Radon is a noble gas in the uranium decay series with a fairly long half life of 3.8 days. Being an inert gas it can easily disperse into the atmosphere as soon as it is released. The solid alpha active decay products of radon (2'^Po, ^'''Po) become airborne and attach themselves to the dust particles, aerosols and water droplets in the atmosphere. When inhaled, these solid decay products along with air may get deposited in the tracheo-bronchial (T-B) and pulmonary (P) region of lungs resulting in the continuous irradiation of the cells by a-particles which may cause lung cancer (3- 5).Radon in dwellings is generated from radium present or existing or accumulated in soil, construction materials and water. Radon and its daughter products pose a significant health hazard, especially when concentrated in some enclosures such as underground mines, caves, cellars or poorly ventilated and badly designed houses. The dwellings selected for the present radon study are situated along the south west coast of Kerala in Thankassery town in Kollam district. Thankassery town is in the vicinity of the High Background Radiation Area (HBRA). Radon and its progeny were measured using solid state nuclear track detectors. EXPERIMENTAL METHOD For the measurement of Potential Alpha Energy Concentration (PAEC) in V/L units from radon and its daughter products, small strips of LR-115 type II Solid Sate Nuclear Detectors (SSNTDs) were employed. The pieces of the detector film of size 2x2 cm, fixed on a thick flat card were exposed in "bare" mode shown in Fig. 1 by hanging the cards on the wall in the room for a period of 90 days such that the detector viewed a hemisphere of radius at least 6.9 cm, the range of ^'"Po a-particles in the air. No surface was closer than this range as the decay products would act as an indeterminate source of a-particles. Detectors were mounted vertically and the locations were so selected that the dust collection on the detectors be minimum. After exposure, the detectors were collected and brought back to the laboratory for analyses. The films were etched in 2.5 NNaOH solution at 60°C for 90 min in a constant temperature water bath. The counting of alpha tracks was done using a binocular optical research microscope with a magnification of 400X. The track density registered in the bare detector will, therefore, be a function of radon progeny concentration in air. The radon concentration in Bqra"^ was estimated from working level by using the following equation (d).: CHEM. ENVIRON. RES. 15 (3 & 4 ) 2006 289 WL X 3700 RC(Bqm-0= The equilibrium factor for radon has been taken as 0.4 as suggested by UNSEAR, (7). To obtain the Potential Alpha Energy Concentration (PAEC) of radon progci^y in mWL, it is essential that LR-115 type II detector films should be calibrated with a known radon concentration under the condi tions almost similar to those which prevail in Indian dwellings. For this purpose, the detectors were calibrated in a radon exposure chamber at the facility available in Environmental Assessment Division of Bhabha Atomic Research Centre, Mumbai (8, 9). The mean calibration factor for LR-115 type II detector was found to be 442 tracks. cm"^d"'perWL. 2 X 2cm LR -115 Type H Plastic Track Detector , Fig.l Bare mode Technique RESULTS AND DISCUSSION Table 1 presents the measured PAEC values of radon daughters in mWL units, radon concentration in Bqm"^ and annual effective dose equivalents in mSv. The radiation doses to the basal layer of epithelium are estimated in terms of the effective dose equivalents using the conversion factor of 9 mSv / WLM suggested by ICRP-65 {10). The measured radon concentration in the dwellings of Thankassery town varies from 44.3 Bqm"' to 373.3 Bqm"^ with an average value of 144.7 ±61.5 Bqm'^ .The radon activity may vary with the ventilation conditions, type of construction materials and other factors. Majority of the houses built in the region are constructed with brick waMs and the remaining houses have either wooden or thatched walls. 34% of the houses are made up of concrete roofs, about 38% are tiled, 12% are thatched and remaining houses have either asbestos or galvanized iron sheets roofs. About 84% of the houses have cement flooring, 8% have tiled flooring and remaining have 290 A. K. MAtnjR et al. bare soil flooring. In our previous measurements in the dwellings of Panmana town situated in the vicinity of High Background Radiation Area (HBRA) more radon activity was found as compared to those in the dwellings of Thankassery. Living rooms show more activities than from the bed rooms and kitchens. The variation may be due to ventilation conditions. Aimual effective dose equivalent in Thankassery town varies from 1.7 mSv/y to 14.2 mSv/y with an average value of 5,5 ± 2.3 mSv/y. Table 1 Indoor radon levels in dwellings of Thankassery town (Kerala ) Code Location Track Potential Radon Annual eftective No. density alpha activity dose equivalent (Tr/Sq Cm/Day) activity (mWL) (Bqm-^) (mSv/y) Sll Living room 12.8 28.9 237.7 9.1 S21 Living room 8.1 18.2 150.1 5.7 S31 Living room 6.9 15.5 128.0 4.9 S41 Living room 7.1 16.0 131.7 S.l S51 Living room 7.8 17.6 145.1 5.5 S61 Living room 5.5 12.4 102.1 3.9 S7I Living room 6.9 15.5 127.6 4.9 S81 Living room 7.2 16.3 134.7 5.1 S12 Bed room 12.7 28.7 236.1 9.0 S22 Bed room 4.9 11.0 91.2 3.5 S32 Bed room 6.9 15.6 128.9 4.9 S42 Bed room 5.7 12.8 105.8 4.0 S52 Bed room 6.6 14.8 121.8 4.6 S62 Bed room 6.0 13.5 111.8 4.3 S72 Bed room 8.1 18.3 150.5 5.7 S82 Bed room 7.9 17.8 147.0 5.6 S13 Kitchen 20.1 45.4 373.3 14.2 S23 Kitchen 2.4 5.3 44.3 1.7 S33 Kitchen 8.7 19.6 161.3 6.1 S43 Kitchen 5.4 12.3 101.2 3.9 S53 Kitchen 7.2 16.3 134.7 5.1 S63 Kitchen 7.0 15.8 130.4 5.0 S73 Kitchen 7.1 16.1 132.8 5.1 S83 Kitchen 7.7 17.4 143.6 5.5 Average 7.8 17.5 144.7 5.5 S.D. 3.3 7.5 61.5 2.3 Rel. Std. % 12.3 42.8 42.5 41.8 CHEM. ENVIRON. RES. 15 (3 & 4 ) 2006 291 The International Commission on Radiatiod Protection (JO) has recommended that remedial action against radon is justified above a continued effective dose of 10 mSv/y, while an action level within the range of 3-10 mSv per year has been proposed and the action level for radon concentrations should be in the range between 200 and 600 Bqm'\ ACKNOWLEDGEMENT The authors wish to thank, Chairman, Department of Applied Physics, Aligarh Muslim University, Aligarh for providing the facilities for this work and also thankful to the residents of the study area for their cooperation during the field work. Prof Rajendra Prasad wishes to thank, All India Council of Technical Education, Government of India for providing Emeritus Fellowship to carry out this work. Financial assistance provided by Department of Science and Technology (DST), Govt, of India to Dr. Rajesh Kumar as Young Scientist under Fast Track Scheme (Award No.SR/ FTP/PS-31/2004) is gratefully acknowledged. REFERENCES 1. International Commission on Radiological Protection; Protection against radon- 222 at home and at work, ICRP Publication 65, Pergamon Press, Oxford, Annals of ICRP 23(2) (1994). 2. UNSCEAR, United Nations Scientific Committee on the Effect of Atomic Radiation, Annex A: Exposure from Natural Sources. United Nations, New York (1982). 3. J. H. Lubin, Am. J Epidemiol., 140,323 (1994). 4. J. M Samet, J. Natl. Cancer Inst, 81,745 (1989). 5. NRC, Health Effects of radon and other internally deposited alpha emitters. Report of the Committee on the Biological Effects of Ionizing Radiation (BEIR-IV- 1988). 6. A.K Mahur, R. Kumar, P.J. Jojo and Rajendra Prasad, Bulletin of Radiation Protection, 28 (M), 203 (2005). 7. UNSCEAR, United Nations Scientific Committee on the Effect of Atomic Radiation, Annex A: Exposure from Natural Sources, United Nations, New York, (2000). 8. A.K. Singh, A. J. Khan and Rajendra Prasad, Radiat. Prot. Dosimetry, 74,189 (1997). 9. PJ. Jojo, A.J. Khan, R.K Tyagi, TV. Ramchandran, M.C. Subba Ramu and Rajendra Prasad, Radiat. Meas., 23,715 (1994). 10. ICRP-65, International Commission for Radiation Protection; Protection against radon-222 at home and at work. Annals of the ICRP, 23(2), 1-48, Pergamon Press, Oxford (1993). 306 A. K. MAHUR et al. Study of Radon Exhalation Rate from Different Types of Building Construction Materials Using SSNTDs and Estimation of Lung Cancer Risk A. K. MAHUR', R. KUMAR, A. AZAM, P. J. Jojo"* AND R. PRASAD Department of Applied Physics. Z. H. College of Engineering & Technology, Aligarii Mtslim University, Aligarh-202002, India * Department of Physics, Fatima Mata National College, KoUam-691 001 India. Uranium is a iBdiotoxic element found in trace quantitieii in almost all naturally occurring materials like soil, rock and sand etc. Building materials are derived from these rnaterials. Radon, an inert radioactive gas whose predecessor is uraniuir. is emitted from soil beneath the house and from building materials. Building materials are the main source of radon inside the dwellings. Because of low level of radon emanation from these materials, long term measurements are needed. Can technique using LR-115 type n solid state nuclear track detector has been employtd for the measurement of radon activity and radon exhalation rate fiiom a number of building materials corranonly used f 3r construction in Kerala. Radon activity is found to vary from 75.0 to 2212.7 Bqm*' with .m average value of 477.7 Bqm', rddon exhalation rate from44.0t o 1337 7 mBqm%' with an average value of 286.3 mBqm"'h"' and effective do je equivalent fiom 52 to 157.7 jxS / y' with an average value 33.7 nSv y -^ for different buMing construe don materials. Radon emanation from granite is found to be maximum while cement brick (hollow) and Kad^pa stone give minimum nuJon emanation. In the case of plastered bricks covered with sealants, radon exhalation is found to increase slightly with acrylic exterior and acrylic emulsion while it decreases with others. INTRODUCTION Ever since the genesis, biosphere has been exposed to natural environment radiation originating trom the atomic species like uranium, thoriiun, potassium, and traces of very long-lived naturally occurring nuclides. The technological endeavors of human beings have modified the levels of radiation exposure slightly. The emanation of radon is primarily * Author for correqjondence : e-mail: [email protected] CHEM. ENVIRON. RES. 15 (3 & 4) 2006 307 associated with radium and its ultimate precursor uranium. The radiation dose received by human beings from indoor radon and its progeny is the largest of all doses received either from natural or man-made sources (/). In rooms kept closed for a long duration and in air-conditioned rooms, high radiation levels are possible by the accumulation of radon gas (2). Radon in indoor space originates from walls, floors, ceilings, and soil beneath the floor. Since the nature of building materials and their uranium content vary regionally, the contribution of building materials to indoor radon will also vary. The Southwest coast of the Kerala State in India is known to have very high levels of natural background radiation owing to the rare earths rich monazite sand available in large amount. Sand present in the region is an orthophosphate of thorium and rare earths and typically contains about 9% thorium oxide and 0,35% uranium oxide (3). Here exists a uniqi ^ situation where a large population is being exposed to a high level radiation all through their life-span. The interest in the study of radon is mainly due to its detrimental effect on human health. The organ that is affected most by the inhalation of radon is the lung. Studies have shown that about 5-20% of all lung cancer deaths are attributed to the inhalation of air containing radon and its progeny (4). Some building materials like phospho-gypsum, aerated concrete with alum shale and uranium mine tailings are known to be exceptionally radioactive. In recent years, many industrial waste materials obtained from thermal power plants, chemical and metallurgical industries are being used in building materials like bricks and cements. Materials like furnace slag, fly ash, and by-product gypsum etc. contain significant amount of radio nuclides belonging to uranium and thorium series. Some house 5 built with fly ash mixed concrete blocks were found to show enhant:ed levels of radon concentration (5-5). Use of hollow and concrete bricks has been evolved as a moden\ technique for fast, cheap and sturdy construction of dwellings. Composition of these bricks is different from conventional bricks, which contains only mud a.id water. In order to evaluate the health risks due to radon inhalation it is necessary to identify and evaluate the sources of indoor radon. The objectives of the present study are to investigate the levels of uranium and radon emanation rate.j in the building materials used in the region. Majority of the houses built in tiie region are constructed with brick walls and the remaining houses have either wooden or thatched walls. 34% of the houses are made up of concrete roofs, about 38% are tiled, 12% are thatched and remaining houses have either asbestos or galvanized iron sheet roofs. About 84% of the houses have cement flooring, 8% have tiled flooring 308 A. KL MAHUR et aL and the remaining have bare flooring (5). Therefore, to study the radon emanation rates different types of bricks, cement bricks (hollow and solid), plastered bricks, flooring materials like mosaic, Kadappa, marble, granite, ceramic tile, floor concrete, etc., were selected. At least 3 samples of each material were used for the investigation and the mean values of the results are reported. EXPERIMENTAL METHODS Radon exhalation measurements In order to measure the radon exhalation rate Can technique (P) was used for the radon exhalation measurements. Aplastic Can of known dimension ( 7.5 cm height and 7.0 cm diameter) was sealed by plasticin to the individual building material. In each Can a LR-115 type II plastic detector (2 cm x 2 cm) was fixed at the top inside the Can (Fig. 1) such that the sensitive surface of the detector faces the material and is freely exposed to the emergent radon so that it can record the alpha particles resulting from the decay of radon in the whole volume of the Can and also from ^'^Po and ^'"Po deposited on the inner wall of the Can. In such measurements it is expected that the exhalation rate depends upon the material and the geometry and dimension of the Can. Radon and its daughters will reach an equilibrium concentration after one week or more. Hence the equilibrium activity of the emergent radon can be obtained from the geometry of the Can and the time of exposure. After the exposure for 90 days, the detectors from all the Cans were retrieved. For the revelation of tracks the detectors were etched in 2.5N NaOH at 60 °C for a period of 90 minutes in a constant temperature water bath. Resulting alpha tracks on the exposed face of the detector foils were scanned under an optical microscope at a magnification of 400X. From the track density, the radon activity was obtained using the calibration factor of 0.056 Tr cm^^d' obtained from an earlier calibration experiment (10). For the computation of exhalation rate following expression {9, 11) was used: cwx Ex = — (1) A[T4{e^^-T}] Where E^ is radon exhalation rate (Bqm'^ h"^), C is integrated radon exposure (Bqm-^ h), V is the effective volume of Can (m^), X is the decay constant for radon (h"^), T is the exposure time (h) and A is the area covered by the Can (m^). CHEM. ENVIRON. RES. 15 (3 & 4 ) 2006 309 [ TntekO«teetor ! >Fhslk;C3K BvMi^MMttiii Fig. 1. Assembly for the measurement of radon exhalation rate using "Can technique" (Plastic Can : Diameter 7 cm and Height 7.5 cm ) Risk estimates The risk of lung cancer from domestic exposure due to radon and its daughters can be estimated directly from the effective dose equivalents The risk of lung cancer due to radon and its daughters is estimated from the radon exhalation rate from building materials. The contribution to indoor radon concentration from different building materials can be calculated from the expression (12). E xS C = ~ (2) Rn Vxl Where, C„ E V, X, are radon concentration (Bqm'^), radon exhalation rate (Bqm-^ h-^), room volume (m^) and air exchange rate (h"') respectively. In these calculations, the maximum radon concentration from the building material was assessed by assuming the room as a cavity with S/ V= 2.0 m-' and air exchange rate of 0.5 hK The annual exposure to potential alpha energy E is then related to the average radon concentration Cj^^ by the following expression. 8760.n.KC^ £ [WLM-y-'j = ^ (3) 170 xSlOO 310 A. K MAHUR et al. Where, C^^is in Bq m-^; n, the fraction of time spent indoors; 8760, the number of horn's per year ajid 170, the mmiber of hours per working month. The values of n = 0.8 and F = 0.42 were used to calculate E . From radon p exposure, the effective dose equivalents were estimated by using a conversion factor of 6.3 mSvAVLM {13). RESLLTS AND DISSCUSION Radon activity and radon exhalation rate are measured in a number of building materials commonly used for building construction in the state of Kerala, India. Calculated values of radon activity and radon exhalation rate are presented in Table 1. It can be seen that there is a wide variation in radon exhalation rate of building materials. Radon activity varies from 75 Bqm'^to 2212.7 Bqm^^ with an average value of 477.1 Bqm'^; radon exhalation rat.^ varies from 44 mBqm-^h-* to 1337.7 mBqm-%-^ with an average value of 286.3 mBqm'^h-' whereas the effective dose equivalents for radon decay products vary from 5.2 to 157.7 \xSv y' with an average value of 33.7 ^iSv y\ Table 1 Radon activity, radon exlialation rate and effective dose equivalent from different building construction materials Building material No. of Random Radon Effective Samples Activity Exhiation dose (Bqm-*) rate equivalent (mBqm^ h"') (jiSvyO Brick: Top layer of the furnace 3 435 257 30.3 Brick: Middle layer of the furnace 3 384 231 27.2 Brick Bottom layer of tiie fiunace 3 376 227 26.7 Cement brick (Hollow) 4 75 44 5.2 Cement brick (Solid) 4 235 141 16.6 Plastered brick 4 521 308 36.3 G Concrete 4 307 181 21.3 Mosaic (Ground Floor) 4 231 136 16.0 Kadqjpa Stone 4 98.7 58 6.8 Ceramic Tile 7 459.3 278.5 32.8 Granite 2 2212.7 1337.7 157.7 Marble 2 390.4 236.1 27.8 Nfinimum vahie 75 44 52 Nfeximum value 2212.7 1337.7 157.7 Average Value 477.1 286.3 33.7 S.D. 539.7 326.8 38.5 Rel.Std.% 113.1 114.1 114.2 CHEM. ENVIRON. RES. 15 (3 & 4 ) 2006 311 Table 2 shows radon activity, radon exhalation rate and effective dose equivalent from the plastered brick covered with sealants. Table 2 Radon activity, radon exhalation rate and effective dose equivalent from the plastered brick covered with sealants Materials Radon Activity Radon Exhalation Effective dose (BqmO rate (mBqm^ h') equivalent (jiSv y') Uncovered plastered Brick 521 308 36.3 White acrylic exterior 535 316 37.3 White acrylic emulsion 628 371 43.7 White snowcem 315 186 21.9 White premium enamel 220 130 15.3 Red oxide 489 289 34.1 Radon activity varies from 220 Bqm"^ to 628 Bqm"^ with an average value of 451.3 Bqm"^, radon exhalation varies from 130 mBqm'^h' to 371 mBqm"^ h'' with an average value of 266.6 mBqm"%'. Radon exhalation was found to increase slightly with acrylic exterior and acrylic emulsion while it decreases with others. The radon exhalation rate from building materials varies appreciably from one building material to another. This may be due to the differences of radium content (14) and porosity of the material (75).The results show highest radon emanation from granite while cement brick (hallow) give minimum value. UNSCEAR (16) has reported exhalation rates from walls and floor of half slab thickness 0.1 m and 0.05 m as 5760 mBqm^^h^' and 2860 mBqm'^"^ respectively. The values reported in the present study are less than these values. ACKNOWLEDGEMENT Prof Rajendra Prasad wishes to thank. All India Council of Technical Education, Government of India for providing Emeritus Fellowship to carry out the work. Financial assistance provided by Department of Science and Technology (DST), Govt, of India to Dr. Rajesh Kumar as Young Scientist under Fast Track Scheme (Award No.SR/FTP/PS-31/2004) is gratefully acknowledged. REFERENCES 1. UNSCEAR Report, United Nations Scientific Committee on Effects of Atomic Radiation, UN, New YorkJ^o. E 88 (1988). 2. A.J. Khan, R.Prasad and R.K. Tyagi, Nucl, Tmcks and Rad. Meas., 20, 609 (1992). 312 A. K. MAHUR et al. 3 M. P. Chougaonkar, K.P. Eappen, T.V. Ramachandran, P.G. Shetty, Y.S. Mayya, S. Sadasivan and V. Venkat Raj, J. ofEnv. Rad, 71,275 (2004). 4. M.C. Subba Ramu, T.S. Muraleedharn, T.V. Ramachandran and GN. Sheikh, Bhabha Atorjic Research Centre Report, India, No. 1390 (1987). 5. K. BI'ton^Albicka and J. Pensko, Health Phys.. 41, 548 (1981). 0." Organisation for Economic Cooperation and Development (OECD), Exposure to radiation from the natural radioactivity in building materials. Report by a group of experts of the OECD Nuc lear Energy Agency, Paris (1979). 7. R. Krieger, Betonwerk Fertiteil Techn., 47,468 (1981). 8. P.J. Jojo, A. Rawat, A. Kumar and R. Prasad, Nuclear Geophysics. 7,445 (1994). 9. A. K. Mahur, Rajesh Kumar and Rajendra Prasad, Environmental Geochemistry, 8 (1&2), 300 (2005). 10. A.K. Singh, P.J. Jojo, A.J. Khan, R. Prasad and T.V. Ramachandran, Radiat. Prot. Environ., 3,129(1997). 11. Y. S, Mayya, Radiat. Prot. Dosim., 14,305 (2004). 12. W. W Nazaroff and A. V Nero. (Jr.), A Wiley-inter science Publicatin, New York (1988). 13. ICRP, International Commission on Radiological Protection, '-ub.No.SO, 17, New York (1987). 14. T.V. Ramachandran and M.C. Subba Ramu, M. C, 3,20. (1989). 15. K.H. Folkerts, G Keller and R..Muth, Radiat. Prot. Dosim., 9, 27 (1984). 16. UNSCEAR, Sources and effects of ionizing radiation. United Nations Scientific Com mittee on the Effect of Atomic Radiation, United Nations, New York (2000).