V.M. Choubey

A study of seasonal variations of radon levels in different types of houses

Abstract A study of the seasonal variations of radon and its decay products in the houses of Tehri Garhwal have been carried out by using LR-115, type II plastic track detector. Radon levels were found to be higher in mud houses than in cemented houses. Radon levels were recorded high in winter and autumn and low in summer and rainy season. However, it is measured highest in winter and lowest in the summer. The season/annual ratios for different type of houses vary substantially among different places. These values were found to vary from 0.91 to 1.07 ana 0.85 to 1.14 for cemented houses and mud houses, respectively. Behaviour of indoor radon for different seasons at different places is discussed in detail. The results show that the seasonal variations with indoor radon levels should be taken in to account to calculate annual effective dose equivalent.

Soil-gas radon as seismotectonic indicator in Garhwal Himalaya

Research on earthquake-related radon monitoring has received enormous attention recently. Anomalous behaviour of radon in soil and groundwater can be used as a reliable precursor for an impending earthquake. While earthquake prediction may not yet be possible, earthquake prediction research has greatly increased our understanding of earthquake source mechanisms, the structural complexities of fault zones, and the earthquake recurrence interval, expected at a given location. This paper presents some results of continuous monitoring of radon in soil-gas in Garhwal Himalaya, India. Daily soil-gas radon monitoring with seismic activity and meteorological parameters were performed in the same laboratory system, located at H.N.B. Garhwal University Campus, Tehri Garhwal, India. Radon anomalies along with meteorological parameters were found to be statistically significant for the seismic events within the magnitudes M2.0-M6.0 and epicentral distances of 16-250 km from the monitoring station. The frequent positive and negative anomalies with constant environmental perturbation indicate the opening and closing of micro cracks within the volume of dilatancy by strain energy. The spike-like and sharp peak anomalies were recorded before, during and after earthquakes occurred in the area. The variations in radon concentrations in soil-gas are found to be correlated with seismic activities in the Garhwal Himalaya. The correlation between radon level and meteorological parameters is also discussed.

Relation between soil-gas radon variation and different lithotectonic units, Garhwal Himalaya, India

Abstract Measurements of radon concentration and uranium content in soil and rocks were made in the regions of the Alaknanda and Bhagirathi valleys in the Garhwal Himalaya by using radon emanometry and X-ray fluorescence method, respectively. The data were collected from different lithotectonic units along and across the various regional thrust planes, faults, shears, etc. The observed values were then correlated with the geological formations and structure of the area. Radon concentrations were found to be controlled by lithology, structure and associated uranium mineralization. A positive linear correlation was also observed between soil-gas radon and in situ uranium in the area.

Measurement of radon exhalation rate from soil samples of Garhwal Himalaya, India

Laboratory experiment was performed for the measurement of radon exhalation rate from the soil samples collected from Garhwal Himalayas. This study is accompanied by the measurement of soil-gas radon concentration in the same area. Both results were compared with the geological formation and structure of the area. No correlation was observed between soil-gas radon concentration and radon exhalation rate. However, it was found to be controlled by the lithology, geological structure and uranium mineralization in the area. The relationship between radon emanation, geological formation and occurrence of high indoor radon concentration is discussed.

Precursory signatures in the radon and geohydrological borehole data for M4.9 Kharsali earthquake of Garhwal Himalaya

Continuous recording of different geophysical parameters incorporated at a single location as a unified effort for earthquake precursory through geodynamical changes initiated for the first time in the Garhwal Himalaya, India. A 68 m deep borehole, penetrating into the water table is operated for continuous radon monitoring along with meteorological/geohydrological observations at two points, one at 10 m (in the air column) and the second one at 50 m (within water column) depths from surface. Preliminary studies reveal diagnostic short duration anomalies in radon concentration recorded few days before the occurrence of a nearby moderate M4.9 earthquake at Kharsali on the 23rd of July, 2007. For nearly half of the year, radon emanation at 10 m depth in the closed air column showed definite pattern of daily variations that may be due to the influence of tidal forces, meteorological and other geodynamical phenomena. This pattern is totally missing during June and July, 2007 when few anomalies for small durations were observed out of which two are unique. These two anomalies exceed 2 sigma (standard deviation) from average radon concentration in both positive and negative sides. However, its emanation at 50 m depth (water radon) is almost constant throughout the year 2007 except some disturbances observed to the ending of June and during July. These abnormalities in radon emanation and other parameters in the borehole may be considered precursory to the M4.9 Kharsali earthquake of July 23, 2007 having an epicenter distance of 60 km. The empirical relation used for amount of radon anomaly with the epicenter distance predicts an earthquake of M4.6 and M4.7 with the observed anomaly at 10 m and 50 m observation points respectively after taking a 60 km epicenter distance.

Geology of radon occurrence around Jari in Parvati Valley, Himachal Pradesh, India

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 Bq m −3 . 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.

Preliminary indoor thoron measurements in high radiation background area of southeastern coastal Orissa, India

This paper presents the preliminary results of radon and thoron measurements in the houses of Chhatrapur area of southeastern coast of Orissa, India. This area is one of the high radiation background radiation areas in India, which consists of monazite sand as the source of thoron. Both active and passive methods were employed for the measurements. Radon and thoron concentrations were measured in the houses of Chhatrapur area using twin cup radon dosemeters, RAD7 and radon-thoron discriminative detector (Raduet). Thoron progeny concentration was also measured in the houses using deposition rate measurements. Radon and thoron concentrations in the houses of study area were found to vary from 8 to 47 Bq m(-3) and the below detection level to 77 Bq m(-3), respectively. While thoron progeny concentration in these houses ranges between 0.17 and 4.24 Bq m(-3), preliminary investigation shows that the thoron concentration is higher than radon concentration in the houses of the study area. The thoron progeny concentration was found to be comparatively higher, which forms a base for further study in the area. The comparison between the results of various techniques is presented in this paper.

Measurement of Equilibrium Factor ”F” between Radon and its Progeny and Thoron and its Progeny in the Indoor Atmosphere Using Nuclear Track Detectors

Radon, thoron and their progeny are present in the indoor atmosphere as attached and unattached fractions. The level of ventilation in a house and the plating out of radon/thoron daughters onto surfaces decide the extent of equilibrium between them. Since the daughter products are mainly responsible for the inhaled dose, the measurement of the equilibrium factor, F, between radon/thoron and their progenies is desirable. It is therefore necessary to measure the equilibrium factor for different types of house construction, locations and seasons before projecting the dose from the measurements of radon and thoron. This paper presents the results of the measurement of F between radon, thoron and their progenies in dwellings using the LR-115 type II plastic track detector. The exposures were made with a twin-chamber dosimeter in about 150 houses of different types, distributed at different locations in the Garhwal and Kumaun region of the Himalayas in India. The measured equilibrium factor between radon and progeny varied from 0.02 to 0.90 with an average value of 0.28 while the same factor for thoron and progeny was found to vary from 0.01 to 0.90 with an average value of 0.09. The methods of measurement and results obtained are discussed in detail.

Radon in groundwater of eastern Doon valley, Outer Himalaya

Abstract The radon content in water may serve as a useful tracer for several geohydrological processes. The hydrodynamic factor, presence of radium in host rocks, as well as the soil porosity and permeability control its concentration in groundwater. In order to understand the factors that control the occurrence of radon in groundwater of Doon valley in Outer Himalaya, a total of 34 groundwater samples were collected from handpumps and tubewells covering three hydrogeological units/areas in the eastern part of Doon valley. Radon variation in tubewells and handpumps varies from 25.4±1.8 to 92.5±3.4 Bq / l with an average of 53.5±2.6 Bq / l . A significant positive correlation between radon concentration and depth of the wells was observed in the Doiwala–Dudhli and Jolleygrant areas suggesting that radon concentration increases with drilling depth in areas consisting of sediments of younger Doon gravels, whereas samples of the Ganga catchment show negative correlation. The high radon levels at shallower depths in the Ganga catchment (consisting of fluvial terraces of Ganga basin) indicate uranium-rich sediments at shallower depth.

Seasonal and daily variation of radon at 10 m depth in borehole, Garhwal Lesser Himalaya, India

Mostly accepted and widely reported radon (Rn(222)) measurements, a tool for earthquake precursor research, is a part of multi-parametric geophysical observation in the Garhwal Lesser Himalaya for earthquake related studies. Radon is being recorded continuously at an interval of 15 min at 10 m depth in a 68 m deep borehole. Three years high resolution 15 min data at 10 m depth shows a complex trend and has a strong seasonal effect along with some diurnal, semi-diurnal and multi-day recurring trends. A well-defined seasonal pattern is prominent with a high emanation in summer and low values in winter accounting for about a 30% decrease in count values in winter when the atmospheric temperature is very low at this station located 1.90 km above mean sea level. Diurnal, semi-diurnal and multi-day trends in this time-series are mainly observed during April-May and October-November. This is the period of spring and autumn when there is a high contrast in day-night atmospheric temperature. Hence the high fluctuation in Rn concentration is mainly caused by the temperature contrast between the air-column inside the borehole and the atmosphere above the earths surface.