Mukesh Rawat

Variability of radon and thoron equilibrium factors in indoor environment of Garhwal Himalaya

The measurements of radon, thoron and their progeny concentrations have been carried out in the dwellings of Uttarkashi and Tehri districts of Garhwal Himalaya, India using LR-115 detector based pin-hole dosimeter and DRPS/DTPS techniques. The equilibrium factors for radon, thoron and their progeny were calculated by using the values measured with these techniques. The average values of equilibrium factor between radon and its progeny have been found to be 0.44, 0.39, 0.39 and 0.28 for rainy, autumn, winter and summer seasons, respectively. For thoron and its progeny, the average values of equilibrium factor have been found to be 0.04, 0.04, 0.04 and 0.03 for rainy, autumn, winter and summer seasons, respectively. The equilibrium factor between radon and its progeny has been found to be dependent on the seasonal changes. However, the equilibrium factor for thoron and progeny has been found to be same for rainy, autumn and winter seasons but slightly different for summer season. The annual average equilibrium factors for radon and thoron have been found to vary from 0.23 to 0.80 with an average of 0.42 and from 0.01 to 0.29 with an average of 0.07, respectively. The detailed discussion of the measurement techniques and the explanation for the results obtained is given in the paper.

Measurements of radon and thoron progeny concentrations in dwellings of Tehri Garhwal, India, using LR-115 deposition-based DTPS/DRPS technique

This paper presents the values of radon and thoron progeny concentrations for different seasons in the dwellings of Tehri Garhwal, India. The measurements have been carried out using LR-115 solid-state nuclear track detector-based passive time-integrated direct thoron progeny sensor/direct radon progeny sensor technique. In summer, the radon and thoron progeny have been found to vary from 5.7±0.8 to 153.2±4.3 Bq m(-3) with an average of 37.6 Bq m(-3) and 0.3±0.06 to 3.2±0.19 Bq m(-3) with an average of 1.3 Bq m(-3), respectively. In the rainy season, the radon and thoron progeny have been found to vary from 3.2±0.6 to 120±3.7 Bq m(-3) with an average of 58.2 Bq m(-3) and 0.2±0.05 to 11.3±0.37 Bq m(-3) with an average of 3.4 Bq m(-3), respectively. In autumn, the radon and thoron progeny have been found to vary from 4.1±0.7 to 374.4±6.7 Bq m(-3) with an average of 95.6 Bq m(-3) and from 0.3±0.06 to 30.5±0.60 Bq m(-3) with an average of 6.6 Bq m(-3), respectively. In winter, the radon and thoron progeny have been found to vary from 9.8±1.1 to 188.9±4.8 Bq m(-3) with an average of 70.7 Bq m(-3) and 0.1±0.03 to 7.5±0.30 Bq m(-3) with an average of 2.3 Bq m(-3), respectively. It has been observed that the average value of radon and thoron progeny concentrations is maximum for autumn and minimum for summer seasons. The seasonal variations in radon and thoron progeny concentrations in different houses are discussed in detail.

Analysis of natural radionuclides in soil samples of Purola area of Garhwal Himalaya, India

Naturally occurring radioactive materials are widely spread in the earths environment, being distributed in soil, rocks, water, air, plants and even within the human body. All of these sources have contributed to an increase in the levels of environmental radioactivity and population radiation doses. This paper presents the activity level due to the presence of (226)Ra, (232)Th and (40)K in soil samples of Purola area in Garhwal Himalaya region. The measured activity of (226)Ra, (232)Th and (40)K in collected soil samples of Purola was found to vary from 13±10 to 55±10 Bq kg(-1) with an average of 31±2 Bq kg(-1), 13±10 to 101±13 Bq kg(-1) with an average 30±3 Bq kg(-1) and 150±81 to 1310±154 Bq kg(-1) with an average 583±30 Bq kg(-1), respectively. The radium equivalent activity in collected soil samples was found to vary from 47 to 221 Bq kg(-1) with an average of 115 Bq kg(-1). The total absorbed gamma dose rate in this area was found to vary from 22 to 93 nGy h(-1) with an average of 55 nGy h(-1). The distribution of these radionuclides in the soil of study area is discussed in details.

Measurements of Radon Flux and Soil-Gas Radon Concentration along the Main Central Thrust, Garhwal Himalaya, Using SRM and RAD7 Detectors

Radon in the Earth’s crust or soil matrix is free to move only if its atoms find their way into pores or capillaries of the matrix. 222Rn atoms from solid mineral grains get into air, filling pores through emanation process. Then 222Rn enters into the atmosphere from air-filled pores by exhalation process. The estimation of radon flux from soil surface is an important parameter for determining the source term for radon concentration modeling. In the present investigation, radon fluxes and soil-gas radon concentration have been measured along and around the Main Central Thrust (MCT) in Uttarkashi district of Garhwal Himalaya, India, by using Scintillation Radon Monitor (SRM) and RAD7 devices, respectively. The soil radon gas concentration measured by RAD7 with soil probe at the constant depth was found to vary from 12 ± 3 to 2330 ± 48 Bq·m−3 with geometrical mean value of 302 ± 84 Bq·m−3. Th significance of this work is its usefulness from radiation protection point of view.

Comparative study of various techniques for environmental radon, thoron and progeny measurements

Long-term average concentrations of radon, thoron and progeny were measured in normal and high background radiation areas in India using different techniques. Radon, thoron and progeny concentrations were measured using Raduet, Pin-Hole dosimeter, deposition-based CR-39 and deposition-based direct radon/thoron progeny sensor (DRPS/DTPS) detector system. All these techniques were used at a same time inside an individual dwelling. Radon concentration was recorded higher than thoron concentration in Garhwal Homes (NBRA) while thoron concentration was found relatively higher in the houses of Chhatarpur area (HBRA) in Odisha, India. The values measured with the CR-39 detector-based technique were found comparable with the values measured with the LR-115 detector-based technique. The comparisons of results using various techniques and their usefulness in radiation measurements are discussed in detail.

Micro-Raman and electronic structure study on kinetics of electronic excitations induced monoclinic-to-tetragonal phase transition in zirconium oxide films

Monoclinic-to-tetragonal phase transformation (PT) in sputtering grown zirconium oxide (ZrO2) films on silicon substrates by electronic excitation (EE) induced by swift heavy ion (SHI) irradiation is reported. The density of EEs and the fluences of irradiation were varied for the better insight of phase transformation kinetics. The phase transition is well evident from the investigations using grazing incidence X-ray diffraction (GIXRD) and micro-Raman spectroscopy (mRS). Studies reveal a PT from the monoclinic to tetragonal phase. It is noted that at high fluence of Ag ion irradiation partly PT to cubic phase is also observed. However, it is clear from this study that this PT is not only due to transient temperature induced by SHI, but also attributed to the strain in the lattice created under the influence of the induced density of defects in the lattice. Interestingly, it may be noted that strain is well evident by the stiffening of the characteristic Raman modes of monoclinic phase. The modifications in electronic and local structure revealed using soft X-ray absorption spectroscopy (XAS) and X-ray absorption fine structure (XAFS) and found after fitting of Zr K-edge XAFS that phase transformation from m-ZrO2 to t-ZrO2 and/or c-ZrO2 upon Ni and Ag irradiation. Studies would elucidate a deeper understanding about the kinetics of PT under such non-equilibrium conditions.