|Year : 2017 | Volume
| Issue : 3 | Page : 133-141
Variation of ambient gamma dose rate and indoor radon/thoron concentration in different villages of Udhampur district, Jammu and Kashmir State, India
Sumit Sharma1, Ajay Kumar2, Rohit Mehra3
1 Department of Physics, DAV College, Amritsar; Department of Physics, Dr. B.R. Ambedkar National Institute of Technology, Jalandhar, Punjab, India
2 Department of Physics, DAV College, Amritsar, Punjab, India
3 Department of Physics, Dr. B.R. Ambedkar National Institute of Technology, Jalandhar, Punjab, India
|Date of Submission||23-Aug-2017|
|Date of Decision||25-Oct-2017|
|Date of Acceptance||01-Dec-2017|
|Date of Web Publication||16-Feb-2018|
Department of Physics, DAV College, Amritsar - 143 001, Punjab
Source of Support: None, Conflict of Interest: None
The exposure of natural background radiation imparts a major contribution to inhalation doses received by the public, and its amount depends on the lithology, altitude, and building construction materials. The preliminary results of indoor and outdoor gamma-ray dose rate of Udhampur district, Jammu and Kashmir, India are presented. Indoor radon and thoron gas concentration have also been measured by using the LR-115 based pin-hole detectors in the same villages and the estimated concentrations are within the recommended level of the International Commission of Radiological Protection. For the outdoor environment, the minimum and maximum gamma dose rate were 0.06 and 0.4 μSvh−1, whereas for indoor environment, the minimum and maximum gamma dose rates were 0.09 and 0.21 μSvh−1, respectively. Effects of lithology on indoor radon/thoron concentration and also on gamma dose rates have also been investigated. The average values of annual effective dose from background gamma radiations were well within the safe limit and does not cause health hazard to the inhabitants.
Keywords: Annual effective dose, exposure, Gamma dose rate, indoor radon/thoron, indoor/outdoor environment
|How to cite this article:|
Sharma S, Kumar A, Mehra R. Variation of ambient gamma dose rate and indoor radon/thoron concentration in different villages of Udhampur district, Jammu and Kashmir State, India. Radiat Prot Environ 2017;40:133-41
|How to cite this URL:|
Sharma S, Kumar A, Mehra R. Variation of ambient gamma dose rate and indoor radon/thoron concentration in different villages of Udhampur district, Jammu and Kashmir State, India. Radiat Prot Environ [serial online] 2017 [cited 2022 Aug 18];40:133-41. Available from: https://www.rpe.org.in/text.asp?2017/40/3/133/225584
| Introduction|| |
Indoor gamma exposure is an important contributor to the total exposure of the population to ionizing radiation  and it represents a radiation assurance issue. Therefore, the European Commission taken this issue in consideration and published a guidance report in 2000. Gamma radiation from radionuclides which are characterized by half-lives comparable to the age of the earth, such as K-40 and the radionuclides from the U 238 and Th 232 series and their decay products represents the main external source of irradiation to the human body. The terrestrial gamma rays originated from radioactive nuclides vary significantly, depending on the geological and geographical features of the region. The world average value of annual effective dose (AED) by natural radiation is about 2.4 mSv, of which 52% is due to inhalation exposure. About 92% of this fraction is contributed by the radioactive element radon and its decay products.
Radon, thoron, and gamma radiations are the main source of natural radioactivity in a recent years. The high value of radon concentration in an indoor environment is the pressure driven to radon transport from soil to air. Indoor radon concentration is influenced by some factors: Ability of the soil to exhalate radon, ventilation rate, building materials, lifestyle of the peoples,,, radium content, the emanation factor, and the permeability of the soil. Naturally occurring radioactive materials are found in variable amounts in rocks and soils of different regions and therefore, the amount of terrestrial radiation from rocks and soils varies geographically. The presence of terrestrial radiations due to naturally occurring radioactive materials in the environment may result in an internal dose received by a population through the ingestion or inhalation pathways.
Indoor gamma dose rate measurements have been carried out in several surveys, for obtaining the distribution of gamma radiation exposure or to evaluate the risk associated with it. Exposure to ionizing radiation poses health risk and this risk may include cancer induction, radiation cataractogenesis, and indirect chromosomal transformation depending on the level of exposure. The knowledge of natural radioactivity inside the buildings is important for the determination for the population exposure to radiations.
In the present study, the indoor and outdoor gamma radiation level measurement has been carried out for the first time in the dwellings of Udhampur district of Jammu and Kashmir (J&K) State, India and correlated with the annual average value of indoor radon and thoron concentration of the same dwellings. Radiation gamma dose rate and the effective dose have been calculated for the assessment of radiation exposure to the inhabitants living in the indoor and outdoor environment. Results obtained from the current study have been compared with the results of other national and international studies available from the literature. This study will provide a baseline data of natural radioactivity level in the studied area.
Geology of the area
Udhampur is one of the oldest districts situated in south-eastern part of the J&K state. It is predominantly an Hill District, which enjoys variable climatic conditions, ranging from subtropical to the semi-temperate. The district has a total area of nearly 4550 km 2. The most important physiographic features of the district are forests. The lithostratigraphic units, exposed in the district, range in age from Eocene to Miocene and consist mainly of sedimentary rocks. The types of rocks found the range from interbedded cherty limestone, dolomite, flaggy limestone, and subordinate quartzite and shale. It is assigned Neo-Proterozoic (Riphean) age on the basis of stromatolites., The area under study consists of three formations; (1) Siwalik formation, (2) Murree formation, and (3) Ramban and Sincha group. [Figure 1] and [Figure 2] show the tectonic map of sub-Himalayan zone and surveyed locations of the study area.
|Figure 1: Tectonic map of the sub Himalaya zone between Udhampur and Dharamsala showing local area names to the MWT. MWT: Medlicott–Wadia Thrust|
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|Figure 2: The surveyed locations of Udhampur district, Jammu and Kashmir|
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The middle Miocene to Pleistocene aged rocks is exposed in the Udhampur district of NE India. This succession along the carbonates rocks was grouped with the Agglomeratic slate in the area west of Gulabgarh, whereas in Chenab valley, it was included in the Ramban Formation. The lowermost part consists of hard compact and bright red sandstones and red-purple shales and clays. The middle part consists of light-gray to gray, thin-bedded limestone, and coarse micaccous gray sandstones. The uppermost part is composed of yellowish to brownish, thin bedded, limestone interbedded with shales, marls, and phyllites.
The Murree Formation is a monotonous sequence of buff and purple clays and purple-gray to greenish-gray sandstones. The Pir Panjal Volcanic overlying the agglomeratic slate and is well exposed in the area lying between Gulabgrah and Uri. A band of the Panjal Volcanic has been extending from Nainikhad in the Ravi valley to Pira-Melra in Chenab valley, south of Ramban running almost parallel to the Murree thrust. It unconformably overlies the Gamir Formation, as the rocks of Oligocene age are missing. The sandstones are fine-grained, hard, and compact. The beds of pseudoconglomerate are also found, frequently in Murree Formation. An early to Middle Miocene age has been assigned to the formation on the basis of fauna.
Ramban and Sincha zone
The narrow belt of carbonates succession conformably overlying the Bhimdasa Formation and unconformably overlying by the Agglomeratic slate constitute the Sincha Formation. It is well exposed around Sincha, north of Ramban where it is limited in North by Panjal “Thrust.” In the east, it is continues to Sudh Mahadev and cutsoff again further in the east toward Chauhra. The lithostratigraphy in Sincha Formation is dark-gray dolomite, dark-gray to bluish-gray dolomite, light-gray sandy dolomite, and pinkish limestone. The Sincha Formation was earlier grouped with “Dogra slate,” Ramsu Formation, Agglomeratic slate.
| Methodology|| |
The estimation of indoor radon/thoron gas level was carried in 50 villages of study region for the period of one year from November 2015 to 2016. The whole year is divided into three seasons (winter, summer and rainy). Indoor radon and thoron gas concentration were measured using pinhole based 222 Rn/220 Rn discriminating dosimeters (described in section “Calculation of 222 Rn and 220 Rn gas”). The dosimeters were deployed in each village (average of two to three dwellings in each village). These dosimeters were then retrieved after an exposure of 4 months and processed to obtain time average concentration values. Measurements of indoor gamma dose rate were also carried out during installation and retrieval of the detectors at all locations. After 4 months of deployment, detectors were retrieved and processed.
The global positioning system coordinates and gamma dose rate of the selected locations were also measured.
In the selected villages, the indoor and outdoor gamma radiation level measurements were made by using Dosimeter-Radiometer MKS-03D. It is GM tube based survey meter with digital display and detects gamma radiations ranging from 0.05 to 3.0 MeV. The detection limit of ambient dose equivalent rate ranged between 0.1 μSvh −1 and 0.1 Svh −1. The measurements were made according to standard protocol, i.e., in the air at a distance of one meter above the ground. For every location, three measurements (after every 4 months) were taken and mean value of three measurements of each location was presented. The exposure rate measured in μSvh −1 was converted into absorbed dose (AD) rate nGyh −1 using the following conversions:
1 μSvh −1 = 1000 nGyh −1
Pin hole based 222 Rn/220 Rn dosimeter
The newly designed pin-hole based 222 Rn/220 Rn dosimeter [Figure 3] is a passive detector which gives time-average radon and thoron concentration. It has a single entry for the measurement of radon and thoron gas activity concentration. Gas enters the first compartment of the cup specifically “radon + thoron” chamber through a glass fiber filter paper (0.56 μm). A circular disc is at the center of the cup which isolates the second compartment and act as a 220 Rn discriminator. Four pin holes are at the circular disc (2 mm length and 1 mm diameter) through which gas diffuses to second compartment, i.e., radon compartment. Chambers are coated with metallic powder to have zero electric field so that the decay products of the gasses will remain uniform throughout the volume. The whole description of these cups is discussed by Sahoo 2013. Both chambers have LR-115 (type II) films, which register tracks from incident alphas in respective chambers. The dosimeters are deployed in dwellings following standard protocols. After exposing the dosimeters for required periods, they were retrieved for processing.
|Figure 3: Systematic diagram of single entrance based 222Rn/220Rn dosimeter|
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The solid-state nuclear track detectors from detector were etched in 2.5 N solution of sodium hydroxide at a constant temperature of 60°C for 90 min in a constant temperature bath unit. It was ensured that the process removed the bulk thickness of 4 μm and leaving the residual thickness of the detector 7 ± 1 μm. Then, films were washed and dried. After that, detectors peeled off from the cellulose base, and track density was obtained by using spark counter. The track density obtained was converted into gas concentration (Bqm −3) using calibration factor.
Calculation of 222 Rn and 220 Rn gas
The 222 Rn and 220 Rn gas concentration are measured by using following the relations.
Where CR and CT are radon and thoron concentration, T1 is the track density observed in “radon” compartment, KR is the calibration factor of radon in “radon” compartment for radon (0.0170 ± 0.002 tr.cm −2 per Bq.d –1.m –3), d is the number of days of exposure, T2 is the track density observed in the “radon-thoron” compartment KR´ (0.0172 ± 0.002 tr.cm −2 per Bq.d −1.m −3), and KT (0.010 ± 0.001 tr.cm −2 per Bq.d −1.m −3) are the calibration factors of radon and thoron in “radon-thoron” compartment.,
Calculations of annual effective dose rate
The annual dose resulting from AD attributed to gamma-ray emission from the radionuclides (226 Ra,232 Th and 40 K) is obtained using the formula:
AEDIn = ADIn × DCF × OFIn × T
AEDOu = ADIn × DCF × OFOu × T
Where AED is the annual effective dose equivalent (μSvy −1). AD is absorbed dose. DCF is the dose conversion factor for both indoor as well as outdoor is same and is 0.7 SvGy −1, T is the indoor exposure duration per year (7000 hy −1). OFIn and OFOu are the occupancy factor for indoor (0.8) and outdoor (0.2) effective dose, respectively.
| Results and Discussion|| |
Variation of gamma dose rates
The range of indoor and outdoor gamma-ray dose rate varied from 0.09 to 0.21 μSvh −1 with an average value of 0.13 ± 0.02 μSvh −1 and from 0.06 to 0.4 μSvh −1 with an average value of 0.19 ± 0.08 μSvh −1, respectively in [Table 1]. The maximum values of outdoor and indoor gamma dose rate were found at Kulwanta (0.40 μSvh −1) and Darsoo (0.21 μSvh −1), respectively. The location-wise variation of indoor and outdoor gamma dose rate is shown in [Figure 4].
|Table 1: Indoor radon/thoron concentration, indoor and outdoor gamma dose rate with global positioning system coordinates of villages of Udhampur District, Jammu and Kashmir|
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|Figure 4: Comparision of indoor and outdoor gamma dose rate of studied locations|
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Variation of radon and thoron concentration
The annual average indoor radon concentration measured in selected villages varied from 17 ± 4 to 60 ± 3 Bqm −3 with an average concentration of 29 ± 7 Bqm −3 presented in [Table 1]. The maximum radon concentration was found in Baryalta (Siwalik formation) and minimum in Bali (Murree formation). The measured values of radon concentration were much lower than the reference level recommended by the International Commission of Radiological Protection (ICRP) (100–300 Bqm −3). Except three villages, the observed values of radon concentration is comparable to the world average value (40 Bqm −3) given by the United Nation Scientific Committee on Effects of Atomic Radiation (UNSCEAR). Similarly, thoron concentration varies from 39 to 171 Bqm −3 with an average value of 82 ± 25. The level of thoron concentration in indoor air is higher than the world average value (10 Bqm −3). The observed thoron concentration is much higher than that of radon concentration in the studied region. The variation of indoor 222 Rn and 220 Rn concentration for the covered villages are shown in [Figure 5].
Gamma dose rate–radon correlation
The result shows that the highest values of indoor gamma radiation level did not always correspond with values of radon, which suggests that radon and its progeny contributes little to the gamma radiation level. This is evident from the fact that indoor radon concentration has a weak correlation of 0.32 with the indoor gamma dose rate as seen from the graph in [Figure 6]. The reason for the difference could be attributed to the high ventilation rate in the dwellings.
|Figure 6: Correlation between indoor gamma radiation level and radon concentration in villages of Udhampur district|
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Comparison of results with those for adjoining Jammu district
The indoor and outdoor gamma dose rate was compared with the reported data of adjoining Jammu district. The average indoor and outdoor gamma dose rate of Jammu district (0.12 and 0.13 μSvh −1) was comparatively lower than the Udhampur district which may be due to subsoil structure, construction materials and geology of the area. The study region is exposed with slates, phyllite lithology  and this kind of lithology contains uranium in trace amounts. Therefore uranium and thorium deposits are a source of gamma radiations  which may be the one of the reason of high gamma dose rate then the neighboring district.
Variation of gamma dose rate for different geological areas
Gamma dose rates were also compared in different geological formations (Siwalik, Murree and Ramban and Sincha). The statistical variation of gamma dose rate and radon/thoron concentration is presented in [Table 2] and graphical variation is shown in [Figure 7]. Indoor gamma dose rate and thoron concentration is observed to be slightly higher in Murree formation while radon concentration is found to be comparable in different geological formations. The higher values in Murree formation may be attributed due to purple/red colored sand and clay which are rich sources of thorium.
|Table 2: Geological variation of indoor 222Rn/220Rn concentration and gamma dose rate|
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|Figure 7: (a) Variation of indoor 222Rn and 220Rn concentration in different geological formations. (b) Variation of indoor and outdoor gamma dose rate in different geological formations|
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The AD rate has been calculated for indoor and outdoor gamma radiation level and presented in [Table 3]. The absorbed dose rate for indoor and outdoor environment has been found to vary from 97 to 210 nGyh −1 with an average value of 129 ± 20 nGyh −1 and from 60 to 400 nGyh −1 with an average value of 196 ± 82 nGyh −1, respectively. The world average range of absorbed dose is 60 nGyh −1 given by the UNSCEAR. The calculated values of absorbed dose for indoor and outdoor gamma are generally higher than the recommended level (60 nGyh −1). Therefore, the value of indoor AED rate (AEDIn) is observed to vary from 414 to 896 μSvy −1 with an average of 548 ± 85 μSvy −1. Similarly, the outdoor AED rate varied from 256 to 1707 μSvy −1 with an average value of 835 ± 352 μSvy −1 [Table 3]. ICRP has suggested a guidance level for gamma AED rate as 1000 μSvy −1 and all the values of indoor AED rate are within the limit. 32% (16 villages) locations has higher outdoor AED rate than suggested level.
Annual effective dose due to radon (AEDR) and thoron (AEDT) progeny were calculated from the relation:
AEDR = CR (Bqm −3) × FR × 7000 × 9 (Bqhm −3)−1
Where CR is the average radon concentration in the houses of study area and FR is the globe average of the equilibrium factor for radon and progeny (0.4) given by UNSCEAR. 7000 is the indoor occupancy factor  and 9 is the dose conversion factor for radon and its progeny. The AEDR and progeny in the study area was found to vary from 0.43 to 1.51 mSvy −1 with an average value of 0.73 ± 0.19 mSvy −1 [Table 2]. The measured average values of AEDR are within the recommended limit given by the ICRP. The AEDT and its progeny were calculated by the relation:
AEDT = CT (Bqm −3) × FT × 7000 × 40 (Bqhm −3)−1
Where, CT is the annual average thoron concentration. FT (0.01) is the global average equilibrium factor for thoron and progeny. The annual effective dose rates due to the exposure to thoron and progeny in the houses of study area with dose conversion factor of 40 was found to vary from 0.11 to 0.48 mSvy −1 with an average value of 0.23 ± 0.07 mSvy −1., The AEDT and its progeny are well within the general guidance level of 1 mSvy −1 set by the ICRP.
In this study, we have also obtained the variation of indoor to outdoor gamma dose ratio as given in [Table 3]. The arithmetic mean of indoor to outdoor gamma dose rate has found to be 0.80 ± 0.42 obtained from gamma survey meter. In normal background areas of India, the ratio of indoor to outdoor gamma dose rate is found to be approximately 1.2, particularly in tiled/cemented floor and concrete walls and ceilings. Chougaonkar 2004 has reported the mean value of indoor to outdoor ratio for bricks, cemented and tiled houses. The obtained average values of the ratio is almost same as that of Chougaonkar 2004 because construction materials has less radioactivity content than that of surrounding earth (mean value = 0.8). The higher values of ratio than 1.2 attributes to mud types of houses (wall/floor of mud) and has the radioactivity content greater than that of surrounding soil.
| Conclusions|| |
The present study was performed to give the baseline reference data of natural radioactivity level in Udhampur district. The maximum value of outdoor gamma dose rate was found at Kulwanta, located at the contact of Murree which is exposed with dolomite, limestone, and quartzite lithology. The minimum and maximum values of indoor gamma dose rates were 0.09 and 0.21 μSvh −1, respectively. The variation in measured values from location to location is because these locations fall in different geological formations. Average values of indoor and outdoor gamma absorbed dose rate was higher than the world average value as reported by the UNSCEAR 2000. The maximum average value of indoor radon and thoron concentration were found in third zone having maximum outdoor gamma dose rate.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3]
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