Y.S. Mayya

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.

A model to predict radon exhalation from walls to indoor air based on the exhalation from building material samples.

In recognition of the fact that building materials are an important source of indoor radon, second only to soil, surface radon exhalation fluxes have been extensively measured from the samples of these materials. Based on this flux data, several researchers have attempted to predict the inhalation dose attributable to radon emitted from walls and ceilings made up of these materials. However, an important aspect not considered in this methodology is the enhancement of the radon flux from the wall or the ceiling constructed using the same building material. This enhancement occurs mainly because of the change in the radon diffusion process from the former to the latter configuration. To predict the true radon flux from the wall based on the flux data of building material samples, we now propose a semi-empirical model involving radon diffusion length and the physical dimensions of the samples as well as wall thickness as other input parameters. This model has been established by statistically fitting the ratio of the solution to radon diffusion equations for the cases of three-dimensional cuboidal shaped building materials (such as brick, concrete block) and one dimensional wall system to a simple mathematical function. The model predictions have been validated against the measurements made at a new construction site. This model provides an alternative tool (substitute to conventional 1-D model) to estimate radon flux from a wall without relying on ²²⁶Ra content, radon emanation factor and bulk density of the samples. Moreover, it may be very useful in the context of developing building codes for radon regulation in new buildings.

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.

Wire-mesh capped deposition sensors: Novel passive tool for coarse fraction flux estimation of radon thoron progeny in indoor environments

Deposition-based (222)Rn and (220)Rn progeny sensors act as unique, passive tools for determining the long time-averaged progeny deposition fluxes in the environment. The use of these deposition sensors as progeny concentration monitors was demonstrated in typical indoor environments as conceptually superior alternatives to gas-based indirect monitoring methods. In the present work, the dependency of these deposition monitors on various environmental parameters is minimized by capping the deposition sensor with a suitable wire mesh. These wire-mesh capped deposition sensors measure the coarse fraction deposition flux, which is less dependent on the change in environmental parameters like ventilation rate and turbulence. The calibration of these wire-mesh capped coarse fraction progeny sensors was carried out by laboratory controlled experiments. These sensors were deployed both in indoor and in occupational environments having widely different ventilation rates. The obtained coarse fraction deposition velocities were fairly constant in these environments, which further confirmed that the signal on the wire-mesh capped sensors show the least dependency on the change in environmental parameters. This technique has the potential to serve as a passive particle sizer in the general context of nanoparticles using progeny species as surrogates. On the whole, there exists a strong case for developing a passive system that responds only to coarse fraction for providing alternative tools for dosimetry and environmental fine particle research.

Acrylonitrile Butadiene Styrene (ABS) plastic‐based low cost tissue equivalent phantom for verification dosimetry in IMRT

A novel IMRT phantom was designed and fabricated using Acrylonitrile Butadiene Styrene (ABS) plastic. Physical properties of ABS plastic related to radiation interaction and dosimetry were compared with commonly available phantom materials for dose measurements in radiotherapy. The ABS IMRT phantom has provisions to hold various types of detectors such as ion chambers, radiographic/radiochromic films, TLDs, MOSFETs, and gel dosimeters. The measurements related to pretreatment dose verification in IMRT of carcinoma prostate were carried out using ABS and Scanditronix‐Wellhofer RW3 IMRT phantoms for five different cases. Point dose data were acquired using ionization chamber and TLD discs, while Gafchromic EBT and radiographic EDR2 films were used for generating 2D dose distributions. Treatment planning system (TPS) calculated and measured doses in ABS plastic and RW3 IMRT phantom were in agreement within ± 2%. The dose values at a point in a given patient acquired using ABS and RW3 phantoms were found comparable within 1%. Fluence maps and dose distributions of these patients generated by TPS and measured in ABS IMRT phantom were also found comparable both numerically and spatially. This study indicates that ABS plastic IMRT phantom is a tissue‐equivalent phantom and, dosimetrically, it is similar to solid/plastic water IMRT phantoms. Although this material is demonstrated for IMRT dose verification, it can also be used as a tissue‐equivalent phantom material for other dosimetry purposes in radiotherapy. PACS number: 87.53Kn, 87.55Qr, 87.53Bn and 87.55Km

Electret--a new tool for measuring concentrations of radon and thoron in air.

AbstractElectret is an electrical analogue of a permanent magnet and it carries permanent electrical charge. A negatively charged teflon electret is used for the collection of decay products of radon or thoron (positively charged) formed inside a 10-l. wire mesh chamber whose sides are covered with

Dosimetry of gamma chamber blood irradiator using Gafchromic EBT film.

Gafchromic films are increasingly being used for dosimetry in medical and industrial applications of ionizing radiation because of their favorable characteristics such as self developing in nature, easy to handle, dose rate independent response, insensitivity to normal room lights, high resolution and insensitivity to variation in the environment conditions. The dosimetry measurements using Gafchromic EBT film, Fricke dosimeter and thermoluminescence (TL) dosimeter were carried out on gamma blood irradiators to establish the suitability of Gafchromic EBT film in such applications. The dose rates determined by Gafchromic EBT film, Fricke dosimeter and TL dosimeter powder are found in good agreement to one another within the uncertainty of measurement. The two-dimensional dose distributions determined using Gafchromic EBT film reflects the expected dose distribution inside the sample compartment of the blood irradiator. The results of this study establish Gafchromic EBT film a suitable dosimeter for routine dosimetry on gamma blood irradiators.

Multi-parametric approach towards the assessment of radon and thoron progeny exposures

Conventionally, the dosimetry is carried out using radon and thoron gas concentration measurements and doses have been assigned using assumed equilibrium factors for the progeny species, which is inadequate pertaining to the variations in equilibrium factors and possibly due to significant thoron. In fact, since the true exposures depend upon the intricate mechanisms of progeny deposition in the lung, therefore an integrated approach for the assessment of progeny is essential. In this context, the recently developed deposition based progeny concentration measurement techniques (DTPS: Direct Thoron progeny sensors and DRPS: Direct Radon progeny sensors) appear to be best suited for radiological risk assessments both among occupational workers and general study populations. DTPS and DRPS consist of aluminized mylar mounted LR115 type passive detectors, which essentially detects the alpha particles emitted from the deposited progeny atoms on the detector surface. It gives direct measure of progeny activity concentrations in air. DTPS has a lower limit of detection limit of 0.1 Bq/m(3) whereas that for DRPS is 1 Bq/m(3), hence are perfectly suitable for indoor environments. These DTPS and DRPS can be capped with 200-mesh type wire-screen to measure the coarse fraction of the progeny concentration and the corresponding coarse fraction deposition velocities as well as the time integrated fine fraction. DTPS and DRPS can also be lodged in an integrated sampler wherein the wire-mesh and filter-paper are arranged in an array in flow-mode, to measure the fine and coarse fraction concentration separately and simultaneously. The details are further discussed in the paper.

Preliminary results from an indoor radon thoron survey in Hungary

More than half of the radiation dose of natural origin comes from radon. However, according to some surveys in certain cases, the radiation dose originating from thoron may be considerable. Among the factors disturbing the measurement of radon, the presence of thoron may also influence the measured radon value, making the estimated radiation exposure imprecise. Thoron has previously been surveyed, mainly in Asia; however, recent surveys for some European locations have found that significant thoron concentrations also need to be considered. In this survey, several types of commercially available SSNTDs (solid-state nuclear track detectors) capable of measuring both radon and thoron were placed at the same time in 73 houses and 7 workplaces in Hungary with 3-month exposition periods. In order to measure thoron, the distance of the detector sets was fixed as 15-20 cm from the walls. The radon concentration was measured with five types of SSNTDs: NRPB, NRPB SSI, Raduet, DTPS and DRPS. The first four types had relatively good accordance (within ± 10 %), but the results of the DRPS detectors were considerably lower when compared with other detectors for radon concentrations over 100 Bq m(-3). The thoron averages were provided by two different types of detectors: Raduet and DTPS. The difference between their average results was more than 30 % and was six times the maximum values. Therefore, the thoron measurement results were judged to be erroneous, and their measurement protocol should be clearly established for future work.

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.