Mineralogy of agricultural soil of selected regions of South Western Karnataka, Peninsular India

Agricultural soils of selected regions of Southwestern Karnataka, Peninsular India, were subjected to systematic mineralogical characterization along with the study of soil physical properties. Physical properties such as soil texture and micro porosity were studied using particle size analyses and positron annihilation lifetime analysis (PALS) technique, respectively. The latter was used to analyze micro porosity of agricultural soil. Both major and minor minerals were identified and confirmed by some analytical techniques like thin section study, powder X- ray diffraction, X-ray fluorescence spectroscopy and Fourier transform infrared spectroscopy

Free volume study of poly(chlorotrifluoroethylene) using positron annihilation spectroscopy as a microanalytical tool

Positron lifetimes and X-ray diffraction measurements were carried out on poly(chlorotrifluoroethylene) films annealed between 25 and 215 degrees C. The positron lifetime results were used to determine the free volume and XRD data were used to determine the apparent crystallite size and crystallinity. The glass transition temperature (T-g) of 52 degrees C obtained from positron results is in agreement with that obtained by thermal analysis. The average free volume cell size is 74 Angstrom(3) in films annealed below T-g, and increases to 84 Angstrom(3) in samples annealed above T-g. Although the observed changes in positron lifetime parameters as a function of annealing temperature are small, they are significant for the kind of material investigated. Our observations are explained in terms of thermally activated chain mobility, local relaxations and long-range motions. We further estimate, for the first time, the activation energies in the amorphous and crystalline regions of the polymer using the Goldanskii kinetic relations. Copyright (C) 1996 Elsevier Science Ltd

Morphology of Thermoset Polyimides by Positron Annihilation Spectroscopy

Thermoset polyimides have great potential for successfully meeting tough stress and temperature challenges in the advanced aircraft development program. However, studies of structure/property relationships in these materials have not been very successful so far. Positron annihilation spectroscopy has been used to investigate free volumes and associated parameters. It has been noted that the free volume correlates well with the molecular weight, cross-link density and thermal coefficient of expansion of these materials. Currently no other techniques are available for direct measurement of these parameters. Experimental results and their interpretations will be discussed

Physics Potential of the ICAL detector at the India-based Neutrino Observatory (INO)

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies and path lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial to address some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations. We describe the simulation framework, the neutrino interactions in the detector, and the expected response of the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Its charge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles.Comment: 139 pages, Physics White Paper of the ICAL (INO) Collaboration, Contents identical with the version published in Pramana - J. Physic

Free volume micro probe study of silver ions implanted in polycarbonate

Positron lifetime, UV-VIS absorption and differential scanning calorimetric (DSC) measurements were performed on pristine polycarbonate (PC) and Ag2+-ion-implanted polycarbonate before and after isochronal annealing treatment. UV absorption results indicated the formation of silver clusters in the polymer matrix. The cluster sizes and number of atoms in these clusters were evaluated from UV results. DSC scans for the sample before and after implantation revealed the diffusion of silver ions in the matrix. Further, these results reveal that the T, of the implanted PC decreased from its pristine value before annealing whereas it increased after annealing. This was inferred to be due to the formation of cross-links by Ag2+ ions when implanted but after annealing, the cross-link seemed to decrease, which resulted in increased diffusion. Positron results as a function of annealing temperature revealed that small size clusters may have been formed in the available free volume and there was migration of silver atoms in the polymer matrix due the rearrangement of the polymer chains. From the positron results the activation energy for the diffusion of silver atoms was determined to be 0.6 eV

Characterization of interfacial adhesion in binary polymer blends: a new approach based on positron lifetime study

A new method of characterizing the adhesion at the interface of partially miscible and immiscible binary polymer blends based on free volume concept is described here. The efficacy of the method is tested in four binary polymer blend systems namely PS/PMMA, PVC/EVA, PP/NBR and PVC/SAN. The usefulness of hydrodynamic interaction is exploited which is derived from free volume data to understand the changes at the interface. We understand that if the adhesion at the interface is good it exhibits large negative values for hydrodynamic interaction parameter alpha, a measure of excess friction at the interface. The thermal properties (indicated by T(g)) also improve for this condition. To show that the method is sensitive to the changes at the interface, we modified the interface through microwave and e-beam irradiation and found from a characterization, that blends with polar groups exhibit interface stabilization for microwave irradiation while e-beam is good for blends with no polar or weak polar groups

Thermally induced microstructural changes in cotton fibers: A free-volume study

Abstract I measured positron lifetime in natural polymer–cotton fibers as a function of isochronal annealing temperature in the range 27–290°C. The variations in the positron results indicated structural changes occurring in the cotton fibers and determined the glass-transition temperature as 80°C. Activation energies were measured separately for the crystalline and amorphous regions, indicating the versatility of the technique. These values were close to the OH bond dissociation energy, suggesting OH bond dissociation, the most probable process occurring under thermal treatment. As an extension of the positron results, the molecular weight of the cotton fibers was determined to be 1,200,000 based on free volume, which was within the range suggested for cotton. There seemed to be an indication that crosslinking changed the spiral structure of cotton fibers to the network type. However, this needs to be validated by other measurements. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3336–3345, 200

Positronium formation in carbon fullerenes — myth or reality

Positron lifetimes in C60 and C70 fullerenes have been measured using Positron Lifetime technique. The analyzed lifetime spectra yields a single lifetime component in agreement with the earlier measurements. XRD measurements have also been used to characterize the fullerene samples. The C60 and C70 fullerenes have regular crystallographic face centered cubic structure with lattice constant a = 14.149 Å and 14.903 Å respectively in good agreement with the literature data. The present positron results clearly support the conclusion that positrons do not form positronium in fullerenes

Physical ageing of poly(chlorotrifluoroethylene): A positron annihilation study

Isothermal annealing of poly(chlorotrifluoroethylene) (PCTFE) was carried out at a temperature of 70 degrees C (slightly above T-g) using the positron annihilation lifetime (PAL) technique. Both the o-Ps lifetime and intensity shows systematic variation with ageing time, and its intensity can be represented by two additive decay exponentials. The free volume which is estimated using the Nakanishi et al. equation developed from Tao's model, exhibits Doolittle type free volume relaxation. Physical ageing seems to yield close packing of polymer chains without crystallization. The relaxation time, and the nonexponentiality parameter, were estimated using a Kolrausch-Williams-Watt (KWW) function. (C) 1997 Elsevier Science Ltd