M. P. Chougaonkar

Profiles of doses to the population living in the high background radiation areas in Kerala, India

A sample study of the profiles of radiation exposures to the populations living in the high background radiation areas (HBRAs) of the monazite-bearing region in Kerala, India, has been conducted by monitoring 200 dwellings selected from two villages in this region. Each of these dwellings was monitored for 1 year and the study lasted for a period of 2 years. The indoor gamma ray dose measurements were carried out using thermo luminescent dosimeters (TLDs) and the inhalation doses due to radon, thoron and their progenies were monitored using solid-state nuclear track detector (SSNTD) based twin-cup dosimeters. Outdoor gamma ray dose measurements were carried out using Geiger Muller (GM) tube based survey meters. Annual effective doses were computed, using occupancy factors of 0.8 and 0.2, respectively, for indoor and outdoor, by adding the three components. Occupants of 41.6% of the houses surveyed were observed to receive the annual effective doses ranging between 0.5 and 5 mSv/a, 41.6% between 5 and 10 mSv/a, 10.2% between 10 and 15 mSv/a and 6.6% greater than 15 mSv/a. The inhalation component was generally smaller than the external gamma ray component and on an average it was found to constitute about 30% of the total dose. The paper presents the details of the methodology adopted and the analysis of the results.

Effect of Low and Chronic Radiation Exposure: A Case-Control Study of Mental Retardation and Cleft Lip/Palate in the Monazite-Bearing Coastal Areas of Southern Kerala

A population-based 1:3 age-matched case-control study was conducted during 2006–2009 to assess the role of high-level natural radiation (>1 mSv/year) on congenital mental retardation and cleft lip/palate in the southwest coastal area of Kerala. Dosimetry was carried out in the house where parents resided during conception and the subsequent two trimesters of pregnancy of the study subject. Conditional logistic regression did not suggest any statistically significant association of either mental retardation (n = 445) or cleft lip/palate (n = 116) with high-level natural radiation. The odds of mental retardation and cleft lip/palate among those exposed to high-level natural radiation relative to normal levels of natural background radiation (≤1 mSv/year) were 1.26 (95% CI: 0.91–1.73) and 0.56 (95% CI: 0.31–1.02), respectively, after controlling for gender and maternal age at birth of the study subject. The data did not suggest any dose-related trend in the risk of either mental retardation (P = 0.113) or cleft lip/palate (P = 0.908). Notwithstanding the use of a single dose estimate to reconstruct past radiation exposure and the complex etiology of congenital malformations, it may reasonably be concluded that the prevailing high-level natural radiation in the study area does not appear to increase the risk of either mental retardation or cleft lip/palate among offspring of parents staying in the area.

Indoor radon and thoron levels in Neendakara and Chavara regions of Southern Coastal Kerala, India

Some areas of the world, called high background radiation areas (HBRAs), have anomalously high levels of natural background radiation and the population residing in the areas is exposed to higher levels of radiation doses than other parts of the world where the natural radioactivity contents are normal. In the present investigation, levels of radon, thoron and their progeny are studied in 110 houses in the coastal region of the Kollam district in the state of Kerala, India using the multi-detector twin cup dosimeter. Among these, 10 houses were studied in detail with five dosimeters in each house. Radon activity concentrations were found to vary from 7 to 100 Bqm(-3) and that of thoron from 4 to 66 Bqm(-3) in Neendakara panchayat. In Chavara panchayat, the variations of radon concentrations were from 7 to 83 Bqm(-3) and thoron concentrations were varied from 4 to 86 Bqm(-3). The occurrence of radon and thoron concentrations in the dwellings for both study areas shows that in 50% of the dwellings, the concentration of radon is about 25 Bqm(-3) and in 60% of the dwellings thoron concentration is about 15 Bqm(-3). The ratio of thoron-to-radon concentrations in the dwellings showed a mean value 0.55 (GM=0.45) for the region.

Deposition-based passive monitors for assigning radon, thoron inhalation doses for epidemiological studies

The International Commission on Radiological Protection dose limits for radiation protection have been based on linearly extrapolating the high-dose risk coefficients obtained from the Japanese A bomb survivor data to low doses. The validity of these extrapolations has been questioned from time to time. To overcome this, epidemiological studies have been undertaken across the world on populations chronically exposed to low-radiation levels. In the past decade, the results of these studies have yielded widely differing, and sometimes, contradictory, conclusions. While recent residential radon studies have shown statistically significant radon risks at low doses, high-level natural radiation (HLNR) studies in China and India have not shown any low-dose risks. Similar is the case of a congenital malformation study conducted among the HLNR area populations in Kerala, India. It is thus necessary to make efforts at overcoming the uncertainties in epidemiological studies. In the context of HLNR studies, assigning radon and thoron doses has largely been an area of considerable uncertainty. Conventionally, dosimetry is carried out using radon concentration measurements, and doses have been assigned using assumed equilibrium factors for the progeny species. Gas-based dose assignment is somewhat inadequate due to variations in equilibrium factors and possibly due to significant thoron. In this context, passive, deposition-based progeny dosimetry appears to be a promising alternative method to assess inhalation doses directly. It has been deployed in various parts of India, including HBRAs and countries in Europe. This presentation discusses the method, the results obtained and their relevance to dose assignment in Indian epidemiological studies.

Beta response of LiMgPO4:Tb,B based OSL discs for personnel monitoring applications

Properties such as high optically stimulated luminescent (OSL) sensitivity, ease of preparation and dose linearity over nine decades (µGy-kGy) make LiMgPO4:Tb, B (LMP) a unique phosphor for dosimetry applications. This led to the investigation of the beta response of highly sensitive LMP-based Teflon-embedded OSL discs for personnel monitoring applications. A PTB beta secondary standard calibration setup (BSS2), which contains three beta sources viz. (147)Pm, (85)Kr and (90)Sr/(90)Y, was used. The relative response with respect to (137)Cs photons for 0.4-mm thick LMP discs was found to be ∼7.32, ∼53.5 and 100 % for (147)Pm, (85)Kr and (90)Sr/(90)Y beta energies, respectively. The response of LMP discs under various filter combinations viz. 0.18-mm thick mylar (25 mg cm(-2)), 0.625-mm thick Poly-allyl-diglycol carbonate (PADC, 81 mg cm(-2)), 1-mm thick polythene (95 mg cm(-2)), 1-mm thick Perspex (118 mg cm(-2)), 1.25-mm thick PADC (162 mg cm(-2)) and 1.6-mm thick (189 mg cm(-2)) Perspex filters was also studied and the ratio of the response of open disc to the response under filters (DOpen/DFilter) of different thicknesses (mg cm(-2)) was evaluated. Studies were also performed for the mixed field of low- ((85)Kr) and high-energy ((90)Sr/(90)Y) beta particles and the DOpen/DFilter ratio was evaluated. The angular dependence of the response of OSL discs to (85)Kr and (90)Sr/(90)Y beta sources was also studied. Studies were also carried out for (204)Tl, (32)P, natural uranium and (106)Ru/(106)Rh beta sources and the ratios of the response of open disc to that of under 1.6-mm thick Perspex (DOpen/DFilter) filter were measured. A study with various beta sources for the evaluation of the DOpen/DFilter ratio was necessary as these ratios are used to estimate the energy of beta particles and to apply the correction factor while evaluating the beta dose/design of dose estimation algorithms.

Performance Characteristics of Newly Modified CaSO4:Dy based Indigenous Thermoluminescent Dosimeters for Environmental Radiation Monitoring

Environmental gamma radiation monitoring around the nuclear installations in India is being carried out for over three decades. This programme was essentially based on powder based Thermoluminescent Dosimeters (TLDs) using naturally occurring calcium fluoride (Fluorite) powder. Being powder based, it was labor intensive and to cater to the increasing demand for monitoring new stations, it was necessary to go for automatic TLD reader system. This was achieved by modifying the TLD cards suitably and using the automated PC based TLD badge TLD reader system indigenously developed and being used for personal dosimetry in India. This paper discusses the modifications that were carried out to make the TLDs suitable for environmental gamma monitoring using TLDs. Performance characterisation of the TLDs like accuracy, precision and energy dependence etc were carried out to see the efficacy of the system for use in the environmental gamma radiation monitoring. In addition, inter-comparison with the existing TLD system, both deployed simultaneously in the field was also carried out. It was found that the new TLD exhibit the accuracy of 89–96 % of the various delivered doses in the laboratory while the precision was observed to be within 4% for all the doses delivered. The gamma radiation levels as measured using two TLD systems were found to match very well with each other. The paper also discusses the results.

Optically stimulated luminescence in LiCaAlF6:Eu2+ phosphor

Results on optically stimulated luminescence (OSL) in LiCaAlF6:Eu(2+) are reported. Continuous wave OSL signal as recorded using blue (470 nm) stimulation was found to be ~31% that of standard phosphor lithium magnesium phosphate. The rate of OSL depletion for standard phosphor lithium magnesium phosphate is only three times less as compared with that of LiCaAlF6:Eu(2+). Strong photoluminescence (PL) in the near ultraviolet region is observed for LiCaAlF6:Eu(2+) with the characteristic Eu(2+) emission at 369 nm for 254 nm excitation. The thermoluminescence (TL) glow peak for LiCaAlF6:Eu(2+) was observed at around 180°C. The glow peak was about six times more intense compared with the dosimetric peak of the well known thermoluminescence dosimetric (TLD) phosphor LiF-TLD 100. Thus this phosphor deserves much more attention than it has received until now and may be useful as a dosimetric material in radiation dosimetry.

Inhalation and external doses in coastal villages of high background radiation area in Kollam, India

The observational evidence for radiation-induced health effects in humans comes largely from the exposures to high doses received over short periods of time. The rate of induction of any health risk at low doses and dose rates is estimated by extrapolation from observations at high doses. Effects of low dose/low dose rate could be done by the study of populations that have been exposed to slightly above-average natural radiation doses. Southwest coastal line of the Kerala state in India is one such region known to have elevated levels of background radioactivity mainly due to the mineral-rich sand available with high abundance of thorium. In the present work, a study was conducted to investigate the inhalation and external radiation doses to human beings in the high background radiation area along the southwest coast of Kerala. Five hundred dwellings were selected for the study. All the selected houses were at least 10 y old with similar construction. Long-term integrated indoor measurements of the external gamma dose using thermoluminescent dosemeters (TLDs) and the inhalation dose with the SSNTD-based twin-cup dosemeters were carried out in the dwellings simultaneously. Ambient gamma dose measurements were also made with a GM tube-based survey meter while deploying and retrieving the dosemeters. The data show a high degree of heterogeneity. The inhalation dose was found to vary from 0.1 to 3.53 mSv y(-1) and the external dose rates had a range of 383-11419 µGy y(-1). The external doses measured by the survey meter and TLDs showed an excellent correlation.

Preliminary study on the measurement of background radiation dose at Antarctica during 32 nd expedition

A significant proportion (10%) of the natural background radiation is of cosmic origin. Cosmic ray consists of gamma, protons, electrons, pions, muons, neutrons and low Z nuclei. Due to the geomagnetic effect, cosmic radiation levels at poles are higher. As a consequence, personnel working in Antarctica (or Arctic) are subjected to high level of cosmic radiation. The present study gives the details of the estimation of background radiation (neutrons, gamma and electrons) dose rate around the Indian station at Antartica named Bharati measured during 32 nd Indian scientific expedition to Antarctica (32 nd INSEA). The measurement was carried out by passive dosimeters such as TLDs and CR-39 and active dosimeter such as RadEye G portable gamma survey meter. Gamma and electron components were measured using TLDs and survey meter, whereas CR-39 SSNTDs and neutron sensitive TLDs were used for neutron measurements. These detectors were deployed at few selected locations around Bharati station for about 2u038d months during summer expedition. The neutron detectors used in the study were pre-calibrated with 241 Am-Be fast/thermal neutron source. The fast neutron dose rate measured based on CR-39 detector was found to about 140-420 nSv/h. The gamma dose rate evaluated by TLDs/survey meter are in the range of 290-400 nSv/h.

Ambient gamma radiation levels (indoor and outdoor) in the villages around Jaduguda (India) using card-based CaSO4: Dy TL dosemeters

A systematic study of the gamma radiation levels (indoor and outdoor) in the villages surrounding the uranium-enriched regions around Jaduguda, India has been undertaken by monitoring selected dwellings in six villages. Each dwelling unit was monitored for a total duration of 1 y. The gamma radiation measurements were carried out using card-based CaSO(4): Dy thermoluminescent dosemeters. The estimated average annual gamma dose values for indoor and outdoor were 980 and 924 (µGy y(-1)), respectively, for the entire region studied. The maximum indoor and outdoor gamma doses experienced in North Dungridih and South Dungridih villages were 1305 and 1223 (µGy y(-1)), respectively. The minimum indoor and outdoor gamma dose values observed in Chatikocha village were 624 and 696 (µGy y(-1)), respectively. Seasonal variation of the indoor gamma values was not observed during the year; however, a small variation was seen with the type of building materials used for construction purposes. A statistical analysis was attempted to characterise the distribution of terrestrial gamma radiation obtained in the study area. The average quarterly indoor gamma values for spring, summer, monsoon and winter seasons as prevalent in the regions were 267±71, 262±54, 213±91, 238±66 (µGy 90 d(-1)), respectively. The annual effective doses to the local population residing in the selected dwelling units were estimated to be 0.6 and 0.1 (mSv y(-1)) for indoor and outdoor, respectively, using an occupancy factor of 0.8 and 0.2.