• S Roy

      Articles written in Pramana – Journal of Physics

    • Fragmentation of positronium in collision with Li ion including electron loss to the continuum

      S Roy C Sinha

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      Fragmentation of ground state ortho-positronium (Ps) in collision with Li ion (Li+) is studied in the framework of post-collisional Coulomb distorted eikonal approximation (CDEA), giving special emphasis on the dynamics of the electron loss to the continuum (ELC) that occurs when the electron (𝑒) and the positron ($e^{+}$) are very close to each other in the velocity space $(v_{e} \approx v_{p})$. The present model takes account of the two-centre effect on the ejected 𝑒 which is crucial for a proper description of the ELC phenomena. Both the fully differential cross-section (TDCS) and the doubly differential cross-section (DDCS) (energy spectra) are investigated at intermediate and high incident energies. A broad distinct ELC peak centred around $v_{e} \approx v_{p}$ is noted in the 𝑒 energy spectrum in contrast to the sharp ELC peak for a heavy projectile, corroborating the experimental findings. Two salient features are noted in the present study: (i) the shift of the 𝑒 DDCS peak (summed over $e^{+}$ angles) towards higher ejection energy with respect to half the residual energy of the system, (ii) comparison of the 𝑒 and $e^{+}$ energy spectra reflect a strong $e-e^{+}$ asymmetry with respect to the ratio $v_{e}/v_{p} = 1$. Both these features are in qualitative agreement with the experimental observations due to Armitage et al for Ps–He atom system and could be attributed to the post-collisional two-centre effect on 𝑒 due to its parent nucleus $(e^{+})$ and the screened target ion. Two different wave functions of the Li ion are chosen in order to test the sensitivity of the present results with respect to the choice of the wave function.

    • Energy-dispersive X-ray fluorescence study of elemental uptake in cauliflower

      D Gupta J M Chatterjee R Ghose A K Mitra S Roy M Sarkar

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      A109Cd radioisotope-induced energy-dispersive X-ray fluorescence (EDXRF) study has been performed on samples of cauliflower consisting of the flower, the leaves and the associated root soil. The cauliflowers were collected from farms near the main dumping site of municipal solid waste in the city of Kolkata, India and also from uncontaminated farms about 50 km away from the city. A unified calibration approach was undertaken for the elemental analysis of the samples of widely varying matrices. The present study suggests that the elemental concentrations in the root soils and leaves of the samples vary from farm to farm, whereby the concentrations of Cu, Zn and Pb in root soils of MSW-contaminated farms are higher by almost an order of magnitude compared to uncontaminated farms. But, the most notable feature of this study is the strikingly similar elemental concentrations in the edible flower part of all samples irrespective of the type of soil.

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