|Year : 2022 | Volume
| Issue : 2 | Page : 81-87
Regional survey of indoor gamma-radiation and estimation of radiation exposure indexes in and around Vellore district, Tamil Nadu
MohanDas Paul Dinakaran1, Abel Nithya Deva Krupa2, Ramu Suriyan1
1 Department of Physics, Voorhees College, Vellore, Tamil Nadu, India
2 Department of Zoology, Voorhees College, Vellore, Tamil Nadu, India
|Date of Submission||29-Jun-2022|
|Date of Decision||30-Sep-2022|
|Date of Acceptance||23-Oct-2022|
|Date of Web Publication||20-Dec-2022|
MohanDas Paul Dinakaran
Department of Physics, Voorhees College, Vellore - 632 001, Tamil Nadu
Source of Support: None, Conflict of Interest: None
The ambient gamma (γ)-radiation levels were measured in various types of dwellings in and around Vellore district. The survey was performed by using a portable Micro-R Survey Meter NUCLEONIX in different types of dwellings. The background γ-radiation exposure inside the dwelling was obtained in a total of 632 dwellings located in 30 different geographical positions in Vellore and nearby places. From the measured dose values, the radiation exposure indexes were estimated such as absorbed dose rate (ADR) and annual effective dose (AED) for the population. The present study has taken an initiative to formulate the environmental γ-radiation reference level for indoor γ-radiation level in and around Vellore district, Tamil Nadu. The calculated highest mean AED was found in concrete dwellings at 0.58 ± 0.07 mSvy−1. The highest ADR was found to be 1219 μGy/yr in tiled house. Furthermore, the work was extended to find the correlation between the temperatures, time, and type of house with radiation for a day with 2 h of regular time interval in these four types of houses and analyzed with response surface methodology.
Keywords: Ambient gamma radiation, μ- R survey meter and RSM analysis
|How to cite this article:|
Dinakaran MP, Deva Krupa AN, Suriyan R. Regional survey of indoor gamma-radiation and estimation of radiation exposure indexes in and around Vellore district, Tamil Nadu. Radiat Prot Environ 2022;45:81-7
|How to cite this URL:|
Dinakaran MP, Deva Krupa AN, Suriyan R. Regional survey of indoor gamma-radiation and estimation of radiation exposure indexes in and around Vellore district, Tamil Nadu. Radiat Prot Environ [serial online] 2022 [cited 2023 Jan 28];45:81-7. Available from: https://www.rpe.org.in/text.asp?2022/45/2/81/364556
| Introduction|| |
Human beings are exposed continuously by two types of radiation from the terrestrial radionuclide and cosmogenic nuclides. Terrestrial radiations have a greater contribution in the environmental radiation for the population after the radon 232Rn. The population receives an external radiation from the cosmic rays whose concentration depends on the geological and geographical conditions. Furthermore, they have received the radiation from indoor by the building construction materials, i.e., soil, brick, sand, clay, variety of cement, brick, marble, granite, gypsum, and aggregate. Indoor gamma (γ)-dose rate is greater than the outdoor γ-dose rate due to the earth materials that were used for the building constructions also the occupancy factor also is high and the more radiation dose received from the indoor is significant for the human health. People spend their 80% of time in indoor such as dwelling and official places. The building materials contain radionuclides 232Th, 238U, and 40K which are the major sources of the indoor radiation. Environmental radioactivity exists in various geological formations of water, rocks, soil, and air in the earth's environment. Obviously, the indoor γ-radiation exposure is greater than the outdoor γ-radiation exposure due to the construction materials. The population is also affected by the radioactive substances which are in the form of nutrients and food. It may be ingested through various kinds, i.e., inhalation, absorption, and ingestion. Nambi et al. reported that the annual γ-radiation dose rates in India range from 0.28 mSv/yr in western India to about 1.06 mSv/yr in eastern parts of the country.
Manmade radiation exposure to the public is occasional, but environmental γ-radiation is always present in the environment and radiation exposure to the public is continuous in their life. The average worldwide natural radiation exposure level indoors is 0.41 mSv.
The present work is mainly focused on the measurement of indoor γ-radiation level in different types of dwellings located in different types of landscape and also the γ-radiation was analyzed at different timings and temperatures. Quantification of γ-radiation rate inside the dwellings is an imperative work to know the natural radiation level exposed to the population. To the best of our knowledge, no other report is available on exposure rate and exposure indexes from γ-radiation level in and around Vellore region.
| Materials and Methods|| |
The Vellore district area is 6077 sq. km, and it is located between 12°–15° and 13°–15° northern latitude and between 78°–20° and 79°–50° eastern longitude. Towns and villages in Vellore district are surrounded by mountains, connected with rivers and forests. Significantly, the temperature is very high when compared with other districts. The indoor background γ-radiation dose rate was measured by using the survey meter NUCLEONX Micro-R Survey Meter (16 × 2 LCD display based, 1” × 1” plastic scintillator based). The measurements have been taken 1 m above and far from the wall of the various indoor places (Agbalagba, 2017). In each house, 10 readings for 30 s were carried out at different places inside the house at 1 m above the floor and wall, i.e., hall, bedroom, and kitchen. In each type, twenty samples were taken in each location and five readings were taken in various places of the dwellings. The dwellings are categorized according to their type of construction such as concrete houses, i.e., flat and slope roof, tiled house, asbestos sheet house, and mud house. Thirty different regions were taken for the study which includes houses located in different types of geological and geographical positions in and around Vellore district.
The γ-radiation was measured at different indoors in regular intervals of time at varying temperatures. In day time, the γ-radiation was monitored at 2-h regular intervals of time in various types of dwellings, i.e., concrete, sheet, tiled, and mud houses.
Estimation of the annual effective dose from indoor gamma-radiation
In the present study, response surface methodology (RSM) which is one of the statistical tools has been employed to analyze the process parameters (A: indoor; B: time; and C: temperature).
Box–Behnken design (BBD) has been employed to study the levels of significant parameters and the interaction between variables which influence the environmental γ-radiation. In the present model, the annual effective dose (AED) (R1) has been studied. The actual experimental design with three variables and the actual response (R1) were generated by the BBD using Design Expert Software (Version 11.0) (Stat-Ease, Inc. Minneapolis, Minnesota, USA.). In the present study, the experimental design consisted of 17 trials, and the independent variables were studied at three different levels, namely low (−1), medium (0), and high (+1). The second-order polynomial coefficients were calculated and analyzed using the Design Expert Statistical Software (Version 11.0, Stat-Ease, USA).
| Results and Discussion|| |
Gamma-radiation exposure levels
The radiation exposure was measured in the units of microroentgen per hour (μRh−1) and for different types of dwellings which are categorized according to their construction, and in each house, 10 readings were taken in different places for 30 s.
The highest exposure has been measured at Alangayam and Virinjipuram (16 μRh−1). In Vellore city (Ambur and Arcot), it was measured to be 14 μRh−1. The average radiation exposures in concrete houses are 11.87 ± 1.36 μRh−1.
In tiled houses, the maximum exposures were observed to be in Alangayam and Virinjipuram (16 μRh−1) and Ranipet (15 μRh−1). The houses are constructed very closely and the river is present in the middle of the town and also the town has many tanneries. The house walls were made by the construction materials which are the major sources of radionuclide. In Kannamangalam, Kanthili, Thimiri, and Vilapakkam regions, it was observed to be 13 μRh−1 and the lowest radiation level of 6 μRh−1 has been measured in the regions of Chittoor and Anaikattu. The average radiation exposures in tiled houses were found to be 11.07 ± 2.91 μRh−1. The tiled dwellings roof were covered with wooden pieces and special type of materials which were made by recycled clay. These type of houses were seen in very congested area with no sufficient ventilation unlike villages with better space. People have no space to get the good air and the temperature of the house is also somewhat high compared to other places. The geographical position and type of the natural materials for the house construction are the main reasons to get such a high radiation.
Asbestos roof house in the region of Vallam, Ranipet, and Mambakkam showed the measurement of 13, 12, and 11 μRh−1, respectively, and the mean value was observed to be 9.07 ± 1.74 μRh−1 in the range of 7–13 μRh−1. The highest measured γ-radiation in mud houses was found to be 10 and 9 μRh−1 in Thimiri and Vaniyambadi, respectively. Similarly, in Katpadi and Vilapakkam, it was observed to be 8 μRh−1. The mean observed value of mud houses was found to be 6.37 ± 1.52 μRh−1 in the range of 4 μRh−1–10 μRh−1. In a report carried out in Nilgiris district (Gudalur) of Tamil Nadu, a similar result was observed where mud houses have been reported to receive the lowest radiation due to the soil, unfired bricks, and stone and have a coating of thin mud paste. The number of mud houses is less when compared to other types of houses. The measured mean background radiation exposure is high in concrete houses and it is double the value of mud houses.
The radiation exposure indexes and their analyses give a reliable assessment of the risks to the exposed persons. In 2009 Uttarakhand, the background radiation level has been reported in the range of 42.6–83.5 μRh−1 with an average value of 60.3 μRh−1. In our district, the measured radiation has been found to be less than the reported value. Using the measured γ-radiation levels [Table 1], the exposure indexes have been assessed as equivalent dose rate (EDR), absorbed dose rate (ADR), and AED.
|Table 1: Measured background gamma-radiation exposure levels (μRh-1) in various types of houses|
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Absorbed dose rate
The ADR gives the amount of radiation energy deposited for each kilogram of body tissue and biological damage can be estimated according to the types of radiation. The γ-radiation exposure rates measured in μRh−1 were also converted into absorbed rates μGyy−1 using the following conversion factor.
The calculated ADR for five different types of dwelling is represented in [Table 2] for thirty places in and around Vellore district. The maximum ADR was found to be 1219 μGyy−1 n the tiled houses which were recorded at Alangayam and Virinjipuram. In slope concrete house of Kavanur, it was calculated to be 1143 μGyy−1 In flat concrete houses of Kaveripakkam and Ranipet, the ADR was found to be 1067 μGyy−1 with a mean value of 904 ± 103 μGyy−1. A similar effect has been observed in the tiled house in the region of Ranipet, Virinjipuram, and Odukathur. On the other hand, asbestos roof houses at Vallam also show ADR values nearer to the concrete house value (991) and the lowest ADR was observed at 305 μGyy−1 at Virinjipuram mud houses. The variations observed in the ADR for different types of houses in different geographical locations might be attributed to the differences in the natural radioactivity concentration in the soil and the construction materials.
In Vellore district, the minimum and maximum of indoor γ-dose rates were found to be 305 to 1219 μGyy−1. In a previous study, Malathi et al. have reported the mean annual absorbed dose of 2435 μGyy−1 in Kanyakumari region and Mohankumari et al. have been reported the mean annual absorbed dose of 2286.36 μGyy−1 in Shimoga region, respectively. When compared to the above-reported values, the ADR obtained in the present study was found to be less.
In a recent study, the maximum ADR was reported in Sri Lanka from various building construction materials (464.28 μGyy−1) which was found to be less when compared to the mean value (485.22 ± 115.81 μGyy−1) of mud houses in our region. Furthermore, the indoor ADR (4328 μGyy−1) reported in Bangladesh was found to be the highest value in the literature. The estimated indoor ADR value is greater than our region in the following countries, i.e., France (657 μGyy−1), Denmark (473 μGyy−1), Finland (639 μGyy−1), Poland (587 μGyy−1), the United Kingdom (526 μGyy−1), Japan (464 μGyy−1), and the United States (333 μGyy−1) (Muhammad, 2013).
Annual effective dose
The AEDs were calculated from the measured γ-dose rates in each type of dwellings. In a day (24 h), people spend 80% of their time in indoor compared with outdoor, especially women spend more time when compared to men.
The AED equivalent was determined by using the equation:
where AED is annual effective dose, Din is the mean indoor ADR, T (hrs) time converted from year to hour (8760 h), and CC is conversion coefficient for indoor that is 0.8.
[Table 3] shows the estimated AED values of the indoor γ-dose rate in different types of houses. The highest AED value of 0.78 mSv/yr was calculated at Virinjipuram and Alangayam and the AED value of 0.74 mSv/yr was found to be in Ranipet tiled houses. This might be due to the tiled materials in the roof and lacking of ventilation. The AED value of 0.69 mSv/yr was found in concrete houses in various places such as Vellore, Kaveripakkam, Anaikattu, Ambur, and Arcot. The mean AED 0.58 ± 0.07 mSv/yr for concrete houses was found to be the highest than any other type of houses. The minimum and maximum AED values were found to be 0.20 and 0.78 mSv/yr for indoor measurements in our district.
In 2012, the AED was calculated in the Chengam region for the building construction materials showing that the average value of the concrete house is 0.5 mSv/yr which is lesser than our report. Similarly, it confirms the low dose rate for the mud house materials. The highest AED in the concrete and tiled house might be due to the concentration of radionuclide on the building materials as per the previous reports. [Table 4] shows the summary of γ-radiation dose parameters and the estimated exposure indexes in and around Vellore district. From the table, it was observed that the highest γ-radiation exposure is found to be in flat concrete roof (11.87 ± 1.36 μR/h).
|Table 4: Summary of gamma-radiation dose parameters and the estimated exposure indexes in and around Vellore district|
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These results can be attributed to the building materials, and also at the same time, the geographical and geological locations of the places are the determining factors (altitude and latitude). The world average AED (0.4 mSv) has been reported by the UNSCEAR, 2000, and the national average dose of about 0.3 mSv/year has been reported by the UNSCEAR, 2010.
Sivakumar et al. reported that the indoor γ-dose (0.477 mSv/yr) in Nilgiris district which is less than in our region. The maximum indoor AED (1.67–0.477 mSvy−1) in southeast Nigeria has been reported by Isinkaye and Emelue. The AED mean range of 1.83–3.17 mSv has been reported in Bangladesh which is the highest value in the literature.
Optimization of process parameters to estimate the annual effective dose by indoor gamma-radiation
Statistical validation of the model (annual effective dose)
RSM is more advantageous than single parameter optimization as it saves time and raw materials. In the present BBD, 17 runs were carried out indicating 17 combinations of experimental trials and the results were analyzed using quadratic model [Table 5]a and [Table 5]b. [Table 6] shows the analysis of variance which indicates the models fit for the estimated AED values. In order to accept the model, the probability value should be greater than the F-value. The model F-value of 4.62 implies the model is significant. P < 0.0500 indicates model terms are significant. In this case, A and B are significant model terms. Values >0.1000 indicate the model terms are not significant. The lack of fit F-value of 23.01 implies the lack of fit is significant.
|Table 6: Analysis of variance for the annual effective dose using response surface quadratic model|
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[Figure 1]a represents the response surface plot for the estimation of AED by indoor γ-radiation in terms of mSv/yr (R1) with respect to time and indoor (type of house) while the temperature was kept constant at the central value. Maximum radiation dose was found to be observed at indoor: concrete house; time: 8 h, and temperature: 35°C. This was further supported by contour plot that is represented in [Figure 1]b. The perturbation plot [Figure 1]c shows that parameters A and B have much influence on the response (AED).
|Figure 1: (a) Response surface plot showing the interaction between the indoor and time on the AED while the temperature was kept constant. (b) Contour plot of AED with respect to time and indoor. (c) Perturbation plot showing the significant parameters (a and b) on the response (AED). AED: Annual effective dose|
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| Conclusions|| |
The γ-radiation dose rate was measured using a portable survey meter in various dwellings in and around Vellore district, Tamil Nadu. In this study, for each house, the radiation indices, i.e., ADR, EDR, and AED, were estimated from the γ-radiation exposure in different types of dwellings. RSM analysis shows a positive correlation between indoor γ-radiation with increased time and temperature. This systematic study provides that the essential baseline dose level for the assessment of environmental γ-radiation and the indoor γ-radiation reference level were formulated in and around Vellore district, Tamil Nadu.
We would like to express our sincere gratitude to University Grants Commission (UGC) for providing financial assistance under the scheme of UGC-Minor Research Project for Teachers (XII Plan) and also thank our Voorhees College management for their constant support and encouragement.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]