Influence of surface conditions on thermal positron reemission spectra from W(100)

Our measurements trace the temporal dependence of positron reemission spectral features, namely, the reemission intensity, energy and angular distributions with post-cleaning time and oxygen exposure. The unwanted inelastic component in the reemission spectra can be kept at less than 6 % of the total reemitted positrons during long and continuous operation by simply ensuring the cleanliness of the sample with better vacuum level. Simultaneously the other optimized spectral features of the beam can be maintained except for the reemission spectral intensity which decreased with increasing time after cleaning. Even though oxygen at high temperature is used normally in the cleaning process of the tungsten moderators, exposure of the sample to oxygen at room temperature caused an exponential reduction in the reemission yield with exposure time.     

Application of particle induced gamma-ray emission for non-destructive determination of fluorine in barium borosilicate glass samples

Barium borosilicate glass (BaBSG) is proposed as a potential candidate for vitrification of nuclear waste generated from thoria based nuclear reactors. Along with fission products, activation products and many inactive chemicals, like fluorine in the form of HF are expected to be present in the dissolver solution with nuclear waste. As vitrification occurs at high temperature, it is important to quantify fluorine in BaBSG. Due to its complex matrix, most of the wet chemical and nuclear analytical methods encounter problems in the estimation of fluorine. Particle induced γ-ray emission (PIGE) method has been standardized for non-destructive determination of fluorine contents in BaBSG samples utilizing measurement of prompt gamma-rays from ¹⁹F (p, p’γ) ¹⁹F reaction. Experiments have been carried out with thick pellet targets prepared in cellulose matrix using 4 MeV proton beam from the folded tandem ion accelerator at BARC, Mumbai. For obtaining current normalized count rate of interest, beam current variation was monitored by the Rutherford backscattering spectrometry (RBS) method as well as by the in situ approach using an externally added element sensitive to PIGE. In this paper standardization of PIGE methods for F determination, validation of methods using synthetic samples, and application to BaBSG samples are reported.     

A classification of homogeneous operators in the Cowen–Douglas class

An explicit construction of all the homogeneous holomorphic Hermitian vector bundles over the unit disc D is given. It is shown that every such vector bundle is a direct sum of irreducible ones. Among these irreducible homogeneous holomorphic Hermitian vector bundles over D, the ones corresponding to operators in the Cowen–Douglas class Bn(D) are identified. The classification of homogeneous operators in Bn(D) is completed using an explicit realization of these operators. We also show how the homogeneous operators in Bn(D) split into similarity classes.     

Group Rings with Solvable Unit Groups of Minimal Derived Length

Let F be a field of characteristic p > 2 and G a nonabelian nilpotent group containing elements of order p. Write F G for the group ring. The conditions under which the unit group ??(F G) is solvable are known, but only a few results have been proved concerning its derived length. It has been established that if G is torsion, the minimum derived length is ?log₂(p + 1)?, and this minimum occurs if and only if |G′| = p. In the present note, we show that the same holds if G has elements of infinite order.     

Equivalence of the Generalized Vertical Block Linear Complementarity Problems and Linear Complementarity Problems

In this paper, generalization of a vertical block linear complementarity problem associated with two different types of matrices, one of which is a square matrix and the other is a vertical block matrix, is proposed. The necessary and sufficient conditions for the existence of the solution of the generalized vertical block linear complementarity problem is derived and the relationship between the solution set of the generalized vertical block linear complementarity problem and the linear complementarity problem is established. It is proved that the generalized vertical block linear complementarity problem has the P-property if and only if the vertical block linear complementarity problem has the P-property.     

Application of k 0-based internal mono-standard PGNAA for compositional characterization of cement samples

The k ₀-based internal mono-standard prompt gamma-ray neutron activation analysis (IM-PGNAA) method was used for compositional analysis of a cement standard provided by the International Atomic Energy Agency as a part of inter-laboratory comparison exercise. The PGNAA was also applied to a local cement sample for comparison purpose. The concentration ratios of elements with respect Ca were determined using the internal mono-standard method. The concentration ratios were then converted to the absolute concentrations by determining concentration of Ca in the cement using relative method. Concentrations of 11 elements were determined in both sample and standard of cement. The results of cement standard are found to be in good agreement with the certified values. The uncertainties on the elemental concentrations were in the range of 5–10 %.     

Applications of EDXRF and INAA techniques for studying impact of industries to the environment

In this study we present quantitative elemental analysis techniques like energy dispersive X-ray fluorescence analysis and instrumental neutron activation analysis to assess the impact of industrial discharge on environment. Two cases are discussed, i.e., (a) enrichment of zinc levels in the soil (1080 ± 76 mg kg^?1) and zinc uptake ranging between 628 and 40 mg kg^?1 in edible plants and cereals grown in agricultural fields near an active zinc smelter, Rajasthan; (b) depth-wise distribution of Cr, Pb and other metals in the sediment core samples from Sundarban wetland, West Bengal, indicating waste discharge from tanneries and other industries.