K. Rama Reddy

Magnetic field-induced transitions in La0.42Eu0.25Ca0.33MnO3 perovskite manganite

Electrical and magnetic transport properties of polycrystalline La0.42Eu0.25Ca0.33MnO3 manganite perovskite are reported here. Temperature dependence of electrical transport, in 0 and 0.6 T external magnetic fields, shows insulating behaviour down to the lowest measured temperatures. Application of 6 T external magnetic field induces two different transitions: (1) an insulator–metal transition around 110 K and (2) a low temperature upturn in resistance values at 30 K. These field-induced transitions suggest strong competition between various interactions present in these materials; this is further supported by the observation of hysteresis in electrical resistance in thermal cooling and warming cycles of measurement. The observed upturn in resistance values below 30 K is presumably due to the combined effect of weak localization, electron–electron and electron–phonon scattering. Magnetization measurements show a paramagnetic–AFM transition at 50 K, but a deviation from a straight line in the 1/M versus T is observed well above 170 K. These results manifest the competition between various possible interactions present in the system.

Baseline studies of radon/thoron concentration levels in and around the Lambapur and Peddagattu areas in Nalgonda district, Andhra Pradesh, India

Abstract Studies conducted by Atomic Minerals Directorate of Exploration and Research (AMD) of Hyderabad, India had established the presence of higher concentrations of uranium in Lambapur and Peddagattu areas of Nalgonda district, AP, India and it was estimated that it could be a viable source for commercial extraction. The envisaged extraction process involves dispersion of radioactive particulate matter into atmosphere. Environmental radioactive studies in and around proposed mining areas at this point of time will be extremely useful for establishing base line data before a large scale uranium extraction process comes into existence. To this end, Solid State Nuclear Track Detectors were installed to evaluate indoor radon and thoron concentration levels in the dwellings of the area. The geometric means of radon and thoron concentration levels were found to be (7.1±0.2)×101 and (6.7±0.3)×10 1 Bq / m 3 , respectively. Simultaneously, natural background radiation measurements were also made and these levels are found to vary from 770 to 3995 μGy / y in the spatial distribution.

Nanosize effects in Eu doped La0.67Ca0.33MnO3 perovskite

Electrical, magnetic and Mossbauer measurements have been carried out on La0.67−xEuxCa0.33MnO3 (x=0.21 and 0.29) for a comparative study of different grain size materials. The samples have been prepared through sol–gel method and sintered at 700, 800, and 900 °C to achieve nanosized materials. All the prepared samples are found to be single phase having orthorhombic structure. The particle sizes are estimated through x-ray diffraction (XRD) by using the Debye–Scherrer’s formulae and these sizes are further confirmed by transmission electron microscopy (TEM) images. E151u Mossbauer studies reveal that Eu is in 3+ charge state. The isomer shift and full width at half maximum (FWHM) of the Mossbauer peak decrease with the increase in particle size. Reduction in the grain size leads to drastic increase in electrical resistivity in all the samples. The typical metal–insulator transition (MIT) observed in x=0.21 bulk sample disappears with decrease in grain size while an external magnetic field of 8T restores t...

Magnetic, ferroelectric, and spin phonon coupling studies of Sr3Co2Fe24O41 multiferroic Z-type hexaferrite

The magnetic, Raman, ferroelectric, and in-field 57Fe Mossbauer studies of polycrystalline multiferroic Sr3Co2Fe24O41 are reported in this paper. From the magnetization studies, it is observed that the sample is soft magnetic in nature with low temperature magnetic spin transitions like longitudinal to transverse conical structure around 130 K and change in magnetic crystalline anisotropy from conical to planar structure at 250 K. Ferroelectric studies of the sample exhibit the spontaneous polarization at low temperature. Strong spin phonon and spin lattice coupling is observed through low temperature Raman spectroscopy. From the in-field 57Fe Mossbauer spectroscopy, spin up and spin down site occupations of Fe ions are calculated in the unit cell.

Airborne radon and its progeny levels in the coal mines of Godavarikhani, Andhra Pradesh, India*

In India, out of about 0.7 million miners, nearly 0.5 million persons are directly engaged in coal operations. Radon and its progeny levels have been quantified in the coal-mining environment of Godavarikhani, Andhra Pradesh, India using solid-state nuclear track detectors. Seasonal and mine depth variations in radon levels have been recorded resulting in the identification of locations with a high radon level as areas with no mining activity, active mining operational zones and return air ventilation paths. All these radon levels were below the permissible levels. The average concentrations of radon and its progeny levels were found to be 144 +/- 61 Bq m(-3) and 20 +/- 11 mWL (working level) respectively in the two-incline mine, and these values for the five-incline mine are recorded as 315 +/- 71 Bq m(-3) and 30 +/- 9 mWL respectively.

Environmental radioactivity studies in the proposed Lambapur and Peddagattu uranium mining areas of Andhra Pradesh, India

The present work was aimed at the establishment of baseline radioactive data in the proposed Lambapur and Peddagattu uranium mining areas in the Andhra Pradesh state, India. The background concentrations of naturally occurring radioactivity in the near-surface soils of the study areas were estimated and the results were analysed. The (238)U concentration in the near-surface soil of the study area was found to vary from 100 to 176 Bq kg(-1), with a mean of 138±24 Bq kg(-1). (232)Th in the study area soils was found to vary between 64 and 116 Bq kg(-1), with a mean of 83±15 Bq kg(-1). The (40)K concentration was found to vary between 309 and 373 Bq kg(-1), with a mean of 343±20 Bq kg(-1). The mean natural background radiation levels were also measured with thermoluminescence (TL) dosimetry technique and with a µR-survey meter, in the villages of the study area. Dose rates measured by TL are found to vary from 1287 to 3363 μGy y(-1), with a mean of 2509 ± 424 μGy y(-1). The dose rates measured in the same villages with a μR-survey meter were found to be in the range of 1211-3255 μGy y(-1), with a mean of 2524 ± 395 μGy y(-1). The mean radiation levels in the study area are found to be relatively high when compared with (Indian) national and international averages. Correlations among radon, thoron and gamma dose rates were found to be poor. The pre-operational data produced in this work will be useful for comparison with future radiation levels during the proposed uranium mining operations.

Airborne radioactivity levels in dwellings of Khammam district, Andhra Pradesh, India

Abstract Radon/thoron levels are estimated in Khammam district as a part of “Radon/thoron mapping” program in Andhra Pradesh, India. About 100 dwellings were chosen at random covering most parts of Khammam district. Twin chamber cup dosimeters consisting of solid-state nuclear track detectors (SSNTDs, LR-115, Type-II) were used to evaluate the radiation levels at quarterly intervals for a period of one calendar year. The average radon and thoron concentrations were found to be 39.1±13.3 and 19.4±14.9 Bq / m 3 , respectively. Seasonal variations of radon/thoron levels were also studied. Variations of radon/thoron concentration levels with different types of dwellings have been studied. In the bare flooring dwellings thoron levels were found to be highest in comparison to concrete, limestone and marble floorings.

Study of indoor radon and its progeny concentration levels in the surrounding areas of Hyderabad, Andhra Pradesh, India

Abstract Having studied the radon/thoron and their concentration levels in the urban Hyderabad (known for higher concentrations of uranium, thorium and 40 K compared to other metropolitan cities of India), an attempt has been made to measure radon and its progeny levels in its surrounding areas covering the region beyond municipal limits, with an approximate radius of 50 km , using the technique of solid-state nuclear track detectors. The concentration levels of radon and its progeny varied from 3 to 47 Bq / m 3 and 0.04 to 3.5 mWL with arithmetic mean of 11 Bq / m 3 and 0.9 mWL , respectively. These airborne radioactivity levels in the surrounding areas of Hyderabad are found to be less than the activity levels of urban Hyderabad region. Seasonal variations of these activity levels have also been studied. Further, variation of radon and its progeny levels in different types of dwellings were investigated and it is found that the dwellings with bare flooring and mud walls were found to have higher concentration levels. Distribution of dwellings for different radon levels was carried out to unravel the effect of poor ventilation, type of the construction materials used, etc.

Indoor radon levels in urban Hyderabad area, Andhra Pradesh, India

Indoor radon levels in urban areas of Hyderabad, Andhra Pradesh, India were measured by a time integrated method using solid state nuclear track detector-based dosemeters. Results show that the radon levels varied widely in the area ranging from 17 to 311 Bq m(-3) with a geometric mean value of 52.8 Bq m(-3) (GSD=1.7). Cumulative frequency distribution of radon levels gave a best fit on a log-normal scale. Measurements were carried out for 1 y, segregating the measurement periods in accordance with seasonal changes. Soil samples from the region were also analysed for natural radionuclides to study its effect, if any, on indoor radon levels. Dwellings categorised based on construction types showed that the average radon levels in the order tiles (TLE)>asbestos (ASB)>concrete (RCC) for the roof structures. The estimated radon levels in the study area are relatively higher than the countrys average value of 23 Bq m(-3) and global average value of 30 Bq m(-3).

Correlation techniques for the improvement of signal-to-noise ratio in measurements with stochastic processes

Abstract An AC modulation technique is described to convert stochastic signal variations into an amplitude variation and its retrieval through Fourier analysis. It is shown that this AC detection of signals of stochastic processes when processed through auto- and cross-correlation techniques improve the signal-to-noise ratio; the correlation techniques serve a similar purpose of frequency and phase filtering as that of phase-sensitive detection. A few model calculations applied to nuclear spectroscopy measurements such as Angular Correlations, Mossbauer spectroscopy and Pulse Height Analysis reveal considerable improvement in the sensitivity of signal detection. Experimental implementation of the technique is presented in terms of amplitude variations of harmonics representing the derivatives of normal spectra. Improved detection sensitivity to spectral variations is shown to be significant. These correlation techniques are general and can be made applicable to all the fields of particle counting where measurements are amenable to “dual modulation”. The proposed AC modulation technique may be applied in diverse fields like pulse height analysis in nuclear spectroscopy, XRD, XRF, RBS, ESCA, positronium resonance, photon counting etc., for enhancing the S / N ratio.