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Geology of radon occurrence around Jari in Parvati Valley, Himachal Pradesh, India
J. Environ. Radioactivity, Vol. 34, No. 2, pp. 139-147, 1997 Copyright 0 Printed ELSEVIER
PII:SO265-931X(96)00024-0
1996 Elsevier Science Limited
in Ireland. All rights reserved 0265-931X/97$15.00+ 0.00
Geology of Radon Occurrence Around Jari in Parvati Valley, Himachal Pradesh, India
Vinay M. Choubey Wadia Institute
of Himalayan
Geology, 33, General 24800 1, India
Kewal K. Sharma Department
of Physics, H.N.B.
(Received
Garhwal
9 October
Mahadev
Singh Road, Dehra Dun,
& R. C. Ramola
University India
1995; accepted
Campus,
Tehri Garhwal,
26 February
249001,
1996)
ABSTRACT Soil gas and indoor radon concentrations have been measured around Jari in Parvati Valley, Himachal Pradesh, India, to study their relationship with the local geology. Both soil gas and indoor radon concentrations were found to be higher near structurally controlled uranium mineralization. Indoor radon levels in the houses of the study area are considerably higher than the ICRP recommended value of 200 Bqm-“. The high indoor radon concentration found may be attributed to the geology of the area. This area needs more detailed investigation as it may be one of the areas of high radon risk in India. Copyright 0 1996 Elsevier Science Limited
INTRODUCTION Radon enters the human environment through the mechanism of diffusion and transport through the earth’s crust. Many factors control emanations and migration of radon, including the geology and the tectonics of the area. Before the discovery of high radon concentrations in houses, the geological aspects of radon abundance were relevant, 139
140
V. M. Choubey et al.
mainly for uranium exploration and earthquake prediction (Sadvosky et al., 1972; Gaucher, 1976; Warren, 1977; King, 1978, 1980; Wakita et al., 1980; Shapiro et al., 1981; Ramola et al., 1989, 1990). In view of its health hazard, radon is now being monitored all over the world. Efforts have been made to correlate soil gas radon concentrations with factors such as the geology, soil porosity, shears, faults and thrusts (Horton & Rogers, 1945; Lapwood, 1948; Mogro-Camper0 & Fleischer, 1977; Fleischer & Mogro-Campero, 1978; Choubey et al., 1986, 1994; Ramola et al., 1989). Several studies on radon and its correlation with geology have been carried out in different parts of the world (Tanner, 1986; Gunderson et al., 1988; Rose et al., 1988; Crameri et al., 1989), but such studies have not been done in this area. A preliminary survey of soil gas and indoor radon has been carried out in the area between Manikaran and Shat in the Parvati Valley of Himachal Pradesh. The geology of the area has also been investigated for comparisons with the radon data.
GEOLOGY OF THE AREA The area under study in the Parvati Valley comprises Precambrian metasedimentaries now exposed in the deeply eroded ‘Kullu-Rampur window’ under the crystalline thrust sheets. The geology of this area has been studied by various workers (Sharma, 1977; Thoni, 1977; Bhargava, 1983; Misra & Tewari, 1988) and mapped in detail by Sharma (1977); he divided the metasedimentaries of the ‘Kullu-Rampur window’ into three units: Manikaran Quartzite, Green Bed Member and Bhalan Member under Banjar Formation. The Manikaran Quartzite unit is generally finegrained, gritty at places and recrystallized into a fine-grained mosaic of quartz, and has uranium mineralization. The Green Bed Member comprises metabasics, green phyllites and schists. It occurs as a thick mappable unit besides a few interbedded bands with quartzite. The Bhalan Member comprises slates and phyllites intercalated with metabasics and flaggy quartzites. Around Jari, the rocks of the overlying thrust sheet (carbonaceous phyllites, quartz schist with recrystallised limestone bands) form a semi-klippen structure over the Manikaran Quartzite with a thrust contact (Fig. 1). Sharma (1977) correlated these rocks with his Khamrada Member (one of the units of Jutogh Formation) which generally surrounds the Window Zone rocks. The soil cover in the study area is l-2m thick, and is developed on quartzite, phyllite and granites (granitic rocks are located at a higher level a few kilometres north of the sampled sites, not shown in Fig. I). As the
THRUST
,,,
,,
Fig. 1. Gcologicai map of the Manikaran
-
. . .
. .
. ,
. .
. .
. .
.
,,
,,
and shat area showing radon sampling sites and their values.
.
142
V. M. Choubey et al.
predominant rock type is quartzite, soil packing is generally coarse, which is favourable for radon to escape easily through a soil cover.
EXPERIMENTAL
METHOD
The track etch method for radon measurements has been described in detail in several papers. In the present study, plastic containers (5cm in diameter and 25 cm in height) were used as a holder for LR-115 (Type II) film detectors. The 2 x 4 cm strips of LR-115 were fixed inside the plastic containers with the sensitive surface of the film facing towards the open end of the plastic holder (Fig. 2). The experiment suggests that the thick wall of the plastic container prevents the penetration of alpha particles from outside, and the air column of 25cm inside the container is sufficient for alpha particles of radon to be distinguished from those of thoron (Ghosh & Soundararajan, 1984). The whole assembly was kept inverted in an augered hole for a period of 13 days. The films were removed and etched in 2.5 N NaOH solution for 2 h at a temperature of 60°C and scanned under an optical microscope for track density measurements. The calibration factor (1 trackcm -2 h-’ = 0.75 kBq me3), determined by Ramola et al.
Fig. 2. Soil gas measurement
assembly
143
Geology of radon occurrence around Jari
(1989) for similar conditions of exposure, has been used to express radon activity in units of kBqme3. For indoor radon measurements, the LR-11.5 (Type II) films were suspended inside the room and exposed for 13 days. The calibration factor (2.84 x 10V2tracks cme2 day-’ = 1 Bqme3) was determined by the BARC, Bombay (Subba Ramu et al., 1988) and was used to express indoor radon activity in units of Bq rne3.
RESULTS AND DISCUSSION The results of 13 soil gas radon measurements from the study area are given in Table 1. The highest radon values of 8.36-17.95 kBqmW3 are found in soil over the Manikaran Quartzite. Some of the detectors planted near the thrust zone east of Jari also show high radon concentrations (5.01, 5.99 and 8.19kBqme3 for sample nos 7, 11 and 8, respectively). In comparison to the uraniferous Manikaran Quartzite, the Green Bed Member (i.e. metabasics, green phyllites and schists) and the Khamrada Member (slates, phyllites and schists) have yielded three- to four-times lower radon values. The higher radon concentrations in Manikaran Quartzite are attributed to the fracture filled vein and disseminated uranium mineralization. The
TABLE 1
Radon Concentration
Sample no.
1 2 3 4 12
13 5 6 9 10 7 8 11
in Soil Between Manikaran and Shat in the Parvati Valley (Samples Grouped by Geological Unit) Rock type
__ .- ~~-.._ White quartzite (Manikaran Quartzite) Pure massive white quartzite (Manikaran Quartzite) White quartzite with grey bands (Manikaran Quartzite) White massive quartzite (Manikaran Quartzite) Grey massive gritty quartzite (Manikaran Quartzite) Grey massive quartzite (Manikaran Quartzite) Greenish phylhtes and schist (Green Bed Member) Greenish phyllites and schist (Green Bed Member) Grey slates, phyllites and schist (Khamrada member) Grey slates and phyllites (Khamrada member) Grey slates, phyllites and schist (near thrust) Grey slates, phyllites and schist (near thurst) Phyllitic schist (near thrust)
--
Radon concentration (kBqm-‘j 17.95
11.78 12.31 9.47 8.36 11.78 3.81 3.91 3.51
1239 5.01 8.19 5.99
144
V. M. Choubey et al.
well-known Chhinjra uranium mineralization (Das et al., 1972, 1979) lies within the investigated area. These authors reported pitchblende/uraninite occurring in the form of the veins along tensional joints and fold axes, and the selected samples analysed have U308 percentages as high as 0.32. The high radon values in the Manikaran Quartzite are attributed to this radioactive source and its diffusion to the adjoining area through fractures, joints, shears and faults. Rocks of the Khamrada Member are in thrust contact with Green Bed Member rocks. The high values of radon near this thrust (5.01, 5.99 and 8.19 kBq me3) are possibly due to the higher permeability of the thrust zone, which allows radon to travel more easily upward from the depths. The results suggest that the knowledge of geology of the area may be helpful to understand the distribution pattern of soil gas radon near the earth’s surface. Indoor radon concentrations measured in six houses of Parvati Valley vary from 193 to 356 Bqme3 (Table 2). Most of the houses investigated are single storey and are built with stone, bricks, cement and soil. In all the houses, the floor surface is covered with wooden planks. The results show that the houses built with stone and soil have higher radon levels, i.e. 298-356 Bq m-j, compared to houses in which bricks/cut stones have been plastered with cement, which show comparatively lower levels of 193287 Bq rne3. The overall high values of radon in these six houses may possibly be due to poor ventilation conditions, building materials (local quartzite and granites) and easy entry of soil gas radon from the soil through the irregular gaps between the wooden planks covering the floor. However, the measurements have been carried out during summer (May-June) when indoor radon concentrations are expected to be minimum. The recorded values are found to be higher than the recommended level of 200 Bq me3 (ICRP, 1987) and in view of the cold climate of the area, for the most part of the year, forcing people to stay inside, particu-
TABLE2 Indoor Sample no. 14 15 16 17 18 19 “Building material ‘Building material
Radon
Concentration
Rock type Jari” Jari” Shat” Near Takrerh Near Chhinjra’ Jari”
in the Houses Radon concentration
( Bqm-’
287 243 193 356 324 298
either brick or cut stone, plastered with cement; wooden mostly stone and soil; wooden floor.
floor.
j
Geology of radon occurrence around Jari
145
larly during the winter, a detailed investigation is needed to determine the health effects.
CONCLUSIONS
Based on limited data, it may be concluded that soil gas radon concentration depends on the geology, soil porosity, structure (shears, faults and thrusts) and the associated uranium mineralization in the area. The high indoor radon concentration found may be attributed to the geology of the area, and a detailed investigation is needed to justify the results. The study of geological factors with radon measurements is important for identifying the soil and bedrock characteristics that correlate with the above-average concentration of indoor radon.
ACKNOWLEDGEMENTS The authors are grateful to the Director, Wadia Institute of Himalayan Geology, Dehradun for providing the necessary facilities to carry out this investigation. They are also grateful to the house owners for their help and co-operation during this work.
REFERENCES Bhargava, 0. N. (1983). The tectronic windows of the Lesser Himalaya. Him. Geol., 10, 135-55. Choubey, V. M., Agarwal, S. P. & Sharma, K. K. (1986). Preliminary radon studies around Doon Valley using SSNTD. In Nuclear Track, ed. K. K. Sharma. Bishen Singh Mahendra Pal Singh, Dehra Dun, pp. 125-30. Choubey, V. M., Ramola, R. C. & Sharma, K. K. (1994). Soil gas and indoor radon studies in Doon Valley, India. Nucl. Geophys., 8, 49-54. Crameri, R., Brunner, H., Buchli, R., Wemli, C. & Burkart, W. (1989). Indoor Rn levels in different geological areas in Switzerland. Hlth Phys., 57, 29-38. Das, G. R. N., Parthasarathy, T. N., Taneja, P. C. (1972). Uranium mineralization in the pelitic schists in the Kullu Himalaya and its probable origin. Proc. Indian Sci. Acad., 37, 267-76.
Das, G. R. N., Parthasarathy, T. N., Taneja, P. C. & Perumal, N. V. A. S. (1979). Geology, structure and uranium mineralization in Kullu, Himachal Himalaya. J. Geol. Sot. India, 20, 95-l 02. Fleischer, R. L. & Mogro-Campero, A. (1978). Mapping of integrated radon emanation for detection of long-distance migration of gases within the earth: techniques and principles. J. Geophys. Res., 83, 353949.
V. M. Choubey et al.
146
Gaucher, E. (1976). Alphameters: uranium prospecting by radon detection. Can. Mining J., 97, 28-34. Ghosh, P. C. & Soundararajan, M. (1984). A technique for discrimination of Radon (222 Rn) and Thoron (220 Rn) in soil-gas using Solid State Nuclear Track Detectors. Nucl. Tracks., 9, 23-27. Gunderson, L. C. S., Reimer, G. M. & Agard, S. S. (1988). Correlation between geology, radon in soil gas, and indoor radon in the Reading Prong. In Geological Causes of Natural Radionuclides Anomalies, eds M. A. Marikos & R. H. Hansman. Special Publication 4, Missouri Department of Natural Resources, Division of Geology and land Survey, pp. 91-102. Horton, C. W. & Rogers, Jr I. T. (1949). Convection currents in a porous medium. J. Appt. Phys., 16, 367-70. ICRP (1987). ICRP Publications 50. Lung Cancer Risk from Indoor Exposure to Radon Daughters. Pergamon Press, Oxford. King, C. Y. (1978). Radon emanation on San Andreas fault. Nature, 271, 5169.
King, C. Y. (1980). Episodic radon changes in sub-surface soil gas along active fault and possible relation to earthquakes. J. Geophys. Res., 85, 3065-78. Lapwood, E. R. (1948). Convection of a fluid in a porous medium. Proc. Camb. Philos. Sot., 44, 508-21.
Misra, D. K. & Tewari, V. C. (1988). Tectonics and sedimentation of the rocks between Mandi and Rohtang Beas Valley, Himachal Pradesh, India. Geosci. J., 9, 153-172. Mogro-Campero, A. & Fleischer, R. L. (1977). Subterrestrial fluid convection: a hypothesis for long-distance migration of radon within the earth. Earth Planet. Sci. Lett., 34, 321.
Ramola, R. C., Sandhu, A. S., Singh, M., Singh, S. & Virk, H. S. (1989). Geochemical exploration of uranium using radon measurement techniques. Nucl. Geophys., 3, 57.
Ramola, R. C., Singh, M., Sandhu, A. S., Singh, S. & Virk, H. S. (1990). The use of radon as an earthquake precursor. Nucl. Geophys., 4,275-87. Rose, A. W., Washington, J. W. & Greeman, D. J. (1988). Variability of radon with depth and season in a central Pennsylvania soil developed on limestone. Northeastern Environ. Sci., 7, 5 -39.
Sadovsky, M., Nersesov, I. L., Nigmatullavev, S. K., Latynina, L. A., Luckk, A. A., Semenov, A. N., Simbireva, I. G. & Ulomov, V. I. (1972). The processes preceding strong earthquakes in some regions of middle Asia. Tectnophysics, 14, 295-307.
Shapiro, M. H., Malvin, J. D., Tombrello, T. A., Mendenhall, M. H., Larson, P. B. & Whitcomb, J. H. (1981). Relationship of the 1979 Southern California radon anomaly to a possible strain event. J. Geophys. Res., 86, 1725-30. Sharma, V. P. (1977). Geology of Kullu-Rampur belt, H. P. Mem. Geol. Sot. India, 106, 235-407.
Subba Ramu, M. C., Muraleedharan, T. S. & Ramachandrian, T. V. (1988). Calibration of a solid state nuclear track detector for the measurement of indoor levels of radon and its daughters. Sci. Total Environ., 73, 245-55. Tanner, A. B. (1986). Geological Factors that Inj7uence Radon Availability. Indoor Radon. Lewis, Pittsburg, PA (Publ. SP-54, Air Pollution Control Assoc.), pp. 1-12.
Geology of radon occurrence around Jari
147
Thoni, M. (1977). Geology, structural evolution and metamorphic zoning in the Kullu Valley (H.P. India) with special references to the reverse metamorphism. Mitt. Ges. Geol. Bergbaustud. Osterr., 24, 125-97. Wakita, H., Nakamura, Y., Notsu, K., Noguchi, M. & Asada, J. (1980). Radon anomaly: A possible precursor of the 1987 Izu-Oshima-Kinkai earthquake. Science, 207, 882-3.
Warren, R. K. (1977). Recent advances in uranium exploration alpha cups. Geophysics, 42, 982-9.
with electronic
PII:SO265-931X(96)00024-0
1996 Elsevier Science Limited
in Ireland. All rights reserved 0265-931X/97$15.00+ 0.00
Geology of Radon Occurrence Around Jari in Parvati Valley, Himachal Pradesh, India
Vinay M. Choubey Wadia Institute
of Himalayan
Geology, 33, General 24800 1, India
Kewal K. Sharma Department
of Physics, H.N.B.
(Received
Garhwal
9 October
Mahadev
Singh Road, Dehra Dun,
& R. C. Ramola
University India
1995; accepted
Campus,
Tehri Garhwal,
26 February
249001,
1996)
ABSTRACT Soil gas and indoor radon concentrations have been measured around Jari in Parvati Valley, Himachal Pradesh, India, to study their relationship with the local geology. Both soil gas and indoor radon concentrations were found to be higher near structurally controlled uranium mineralization. Indoor radon levels in the houses of the study area are considerably higher than the ICRP recommended value of 200 Bqm-“. The high indoor radon concentration found may be attributed to the geology of the area. This area needs more detailed investigation as it may be one of the areas of high radon risk in India. Copyright 0 1996 Elsevier Science Limited
INTRODUCTION Radon enters the human environment through the mechanism of diffusion and transport through the earth’s crust. Many factors control emanations and migration of radon, including the geology and the tectonics of the area. Before the discovery of high radon concentrations in houses, the geological aspects of radon abundance were relevant, 139
140
V. M. Choubey et al.
mainly for uranium exploration and earthquake prediction (Sadvosky et al., 1972; Gaucher, 1976; Warren, 1977; King, 1978, 1980; Wakita et al., 1980; Shapiro et al., 1981; Ramola et al., 1989, 1990). In view of its health hazard, radon is now being monitored all over the world. Efforts have been made to correlate soil gas radon concentrations with factors such as the geology, soil porosity, shears, faults and thrusts (Horton & Rogers, 1945; Lapwood, 1948; Mogro-Camper0 & Fleischer, 1977; Fleischer & Mogro-Campero, 1978; Choubey et al., 1986, 1994; Ramola et al., 1989). Several studies on radon and its correlation with geology have been carried out in different parts of the world (Tanner, 1986; Gunderson et al., 1988; Rose et al., 1988; Crameri et al., 1989), but such studies have not been done in this area. A preliminary survey of soil gas and indoor radon has been carried out in the area between Manikaran and Shat in the Parvati Valley of Himachal Pradesh. The geology of the area has also been investigated for comparisons with the radon data.
GEOLOGY OF THE AREA The area under study in the Parvati Valley comprises Precambrian metasedimentaries now exposed in the deeply eroded ‘Kullu-Rampur window’ under the crystalline thrust sheets. The geology of this area has been studied by various workers (Sharma, 1977; Thoni, 1977; Bhargava, 1983; Misra & Tewari, 1988) and mapped in detail by Sharma (1977); he divided the metasedimentaries of the ‘Kullu-Rampur window’ into three units: Manikaran Quartzite, Green Bed Member and Bhalan Member under Banjar Formation. The Manikaran Quartzite unit is generally finegrained, gritty at places and recrystallized into a fine-grained mosaic of quartz, and has uranium mineralization. The Green Bed Member comprises metabasics, green phyllites and schists. It occurs as a thick mappable unit besides a few interbedded bands with quartzite. The Bhalan Member comprises slates and phyllites intercalated with metabasics and flaggy quartzites. Around Jari, the rocks of the overlying thrust sheet (carbonaceous phyllites, quartz schist with recrystallised limestone bands) form a semi-klippen structure over the Manikaran Quartzite with a thrust contact (Fig. 1). Sharma (1977) correlated these rocks with his Khamrada Member (one of the units of Jutogh Formation) which generally surrounds the Window Zone rocks. The soil cover in the study area is l-2m thick, and is developed on quartzite, phyllite and granites (granitic rocks are located at a higher level a few kilometres north of the sampled sites, not shown in Fig. I). As the
THRUST
,,,
,,
Fig. 1. Gcologicai map of the Manikaran
-
. . .
. .
. ,
. .
. .
. .
.
,,
,,
and shat area showing radon sampling sites and their values.
.
142
V. M. Choubey et al.
predominant rock type is quartzite, soil packing is generally coarse, which is favourable for radon to escape easily through a soil cover.
EXPERIMENTAL
METHOD
The track etch method for radon measurements has been described in detail in several papers. In the present study, plastic containers (5cm in diameter and 25 cm in height) were used as a holder for LR-115 (Type II) film detectors. The 2 x 4 cm strips of LR-115 were fixed inside the plastic containers with the sensitive surface of the film facing towards the open end of the plastic holder (Fig. 2). The experiment suggests that the thick wall of the plastic container prevents the penetration of alpha particles from outside, and the air column of 25cm inside the container is sufficient for alpha particles of radon to be distinguished from those of thoron (Ghosh & Soundararajan, 1984). The whole assembly was kept inverted in an augered hole for a period of 13 days. The films were removed and etched in 2.5 N NaOH solution for 2 h at a temperature of 60°C and scanned under an optical microscope for track density measurements. The calibration factor (1 trackcm -2 h-’ = 0.75 kBq me3), determined by Ramola et al.
Fig. 2. Soil gas measurement
assembly
143
Geology of radon occurrence around Jari
(1989) for similar conditions of exposure, has been used to express radon activity in units of kBqme3. For indoor radon measurements, the LR-11.5 (Type II) films were suspended inside the room and exposed for 13 days. The calibration factor (2.84 x 10V2tracks cme2 day-’ = 1 Bqme3) was determined by the BARC, Bombay (Subba Ramu et al., 1988) and was used to express indoor radon activity in units of Bq rne3.
RESULTS AND DISCUSSION The results of 13 soil gas radon measurements from the study area are given in Table 1. The highest radon values of 8.36-17.95 kBqmW3 are found in soil over the Manikaran Quartzite. Some of the detectors planted near the thrust zone east of Jari also show high radon concentrations (5.01, 5.99 and 8.19kBqme3 for sample nos 7, 11 and 8, respectively). In comparison to the uraniferous Manikaran Quartzite, the Green Bed Member (i.e. metabasics, green phyllites and schists) and the Khamrada Member (slates, phyllites and schists) have yielded three- to four-times lower radon values. The higher radon concentrations in Manikaran Quartzite are attributed to the fracture filled vein and disseminated uranium mineralization. The
TABLE 1
Radon Concentration
Sample no.
1 2 3 4 12
13 5 6 9 10 7 8 11
in Soil Between Manikaran and Shat in the Parvati Valley (Samples Grouped by Geological Unit) Rock type
__ .- ~~-.._ White quartzite (Manikaran Quartzite) Pure massive white quartzite (Manikaran Quartzite) White quartzite with grey bands (Manikaran Quartzite) White massive quartzite (Manikaran Quartzite) Grey massive gritty quartzite (Manikaran Quartzite) Grey massive quartzite (Manikaran Quartzite) Greenish phylhtes and schist (Green Bed Member) Greenish phyllites and schist (Green Bed Member) Grey slates, phyllites and schist (Khamrada member) Grey slates and phyllites (Khamrada member) Grey slates, phyllites and schist (near thrust) Grey slates, phyllites and schist (near thurst) Phyllitic schist (near thrust)
--
Radon concentration (kBqm-‘j 17.95
11.78 12.31 9.47 8.36 11.78 3.81 3.91 3.51
1239 5.01 8.19 5.99
144
V. M. Choubey et al.
well-known Chhinjra uranium mineralization (Das et al., 1972, 1979) lies within the investigated area. These authors reported pitchblende/uraninite occurring in the form of the veins along tensional joints and fold axes, and the selected samples analysed have U308 percentages as high as 0.32. The high radon values in the Manikaran Quartzite are attributed to this radioactive source and its diffusion to the adjoining area through fractures, joints, shears and faults. Rocks of the Khamrada Member are in thrust contact with Green Bed Member rocks. The high values of radon near this thrust (5.01, 5.99 and 8.19 kBq me3) are possibly due to the higher permeability of the thrust zone, which allows radon to travel more easily upward from the depths. The results suggest that the knowledge of geology of the area may be helpful to understand the distribution pattern of soil gas radon near the earth’s surface. Indoor radon concentrations measured in six houses of Parvati Valley vary from 193 to 356 Bqme3 (Table 2). Most of the houses investigated are single storey and are built with stone, bricks, cement and soil. In all the houses, the floor surface is covered with wooden planks. The results show that the houses built with stone and soil have higher radon levels, i.e. 298-356 Bq m-j, compared to houses in which bricks/cut stones have been plastered with cement, which show comparatively lower levels of 193287 Bq rne3. The overall high values of radon in these six houses may possibly be due to poor ventilation conditions, building materials (local quartzite and granites) and easy entry of soil gas radon from the soil through the irregular gaps between the wooden planks covering the floor. However, the measurements have been carried out during summer (May-June) when indoor radon concentrations are expected to be minimum. The recorded values are found to be higher than the recommended level of 200 Bq me3 (ICRP, 1987) and in view of the cold climate of the area, for the most part of the year, forcing people to stay inside, particu-
TABLE2 Indoor Sample no. 14 15 16 17 18 19 “Building material ‘Building material
Radon
Concentration
Rock type Jari” Jari” Shat” Near Takrerh Near Chhinjra’ Jari”
in the Houses Radon concentration
( Bqm-’
287 243 193 356 324 298
either brick or cut stone, plastered with cement; wooden mostly stone and soil; wooden floor.
floor.
j
Geology of radon occurrence around Jari
145
larly during the winter, a detailed investigation is needed to determine the health effects.
CONCLUSIONS
Based on limited data, it may be concluded that soil gas radon concentration depends on the geology, soil porosity, structure (shears, faults and thrusts) and the associated uranium mineralization in the area. The high indoor radon concentration found may be attributed to the geology of the area, and a detailed investigation is needed to justify the results. The study of geological factors with radon measurements is important for identifying the soil and bedrock characteristics that correlate with the above-average concentration of indoor radon.
ACKNOWLEDGEMENTS The authors are grateful to the Director, Wadia Institute of Himalayan Geology, Dehradun for providing the necessary facilities to carry out this investigation. They are also grateful to the house owners for their help and co-operation during this work.
REFERENCES Bhargava, 0. N. (1983). The tectronic windows of the Lesser Himalaya. Him. Geol., 10, 135-55. Choubey, V. M., Agarwal, S. P. & Sharma, K. K. (1986). Preliminary radon studies around Doon Valley using SSNTD. In Nuclear Track, ed. K. K. Sharma. Bishen Singh Mahendra Pal Singh, Dehra Dun, pp. 125-30. Choubey, V. M., Ramola, R. C. & Sharma, K. K. (1994). Soil gas and indoor radon studies in Doon Valley, India. Nucl. Geophys., 8, 49-54. Crameri, R., Brunner, H., Buchli, R., Wemli, C. & Burkart, W. (1989). Indoor Rn levels in different geological areas in Switzerland. Hlth Phys., 57, 29-38. Das, G. R. N., Parthasarathy, T. N., Taneja, P. C. (1972). Uranium mineralization in the pelitic schists in the Kullu Himalaya and its probable origin. Proc. Indian Sci. Acad., 37, 267-76.
Das, G. R. N., Parthasarathy, T. N., Taneja, P. C. & Perumal, N. V. A. S. (1979). Geology, structure and uranium mineralization in Kullu, Himachal Himalaya. J. Geol. Sot. India, 20, 95-l 02. Fleischer, R. L. & Mogro-Campero, A. (1978). Mapping of integrated radon emanation for detection of long-distance migration of gases within the earth: techniques and principles. J. Geophys. Res., 83, 353949.
V. M. Choubey et al.
146
Gaucher, E. (1976). Alphameters: uranium prospecting by radon detection. Can. Mining J., 97, 28-34. Ghosh, P. C. & Soundararajan, M. (1984). A technique for discrimination of Radon (222 Rn) and Thoron (220 Rn) in soil-gas using Solid State Nuclear Track Detectors. Nucl. Tracks., 9, 23-27. Gunderson, L. C. S., Reimer, G. M. & Agard, S. S. (1988). Correlation between geology, radon in soil gas, and indoor radon in the Reading Prong. In Geological Causes of Natural Radionuclides Anomalies, eds M. A. Marikos & R. H. Hansman. Special Publication 4, Missouri Department of Natural Resources, Division of Geology and land Survey, pp. 91-102. Horton, C. W. & Rogers, Jr I. T. (1949). Convection currents in a porous medium. J. Appt. Phys., 16, 367-70. ICRP (1987). ICRP Publications 50. Lung Cancer Risk from Indoor Exposure to Radon Daughters. Pergamon Press, Oxford. King, C. Y. (1978). Radon emanation on San Andreas fault. Nature, 271, 5169.
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