• Volume 21, Issue 5

      November 1983,   pages  293-345

    • e-H(2S) elastic scattering in the two-potential eikonal approximation

      C N Chandra Prabha H S Desai

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      The differential scattering cross-sections fore−H (2S) elastic scattering are calculated at intermediate energies by using the two-potential eikonal approximation. The results are compared with the recent theoretical data and the conventional Glauber cross-sections.

    • Theory of divalent ions in crystals

      G Raghurama Ramesh Narayan

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      The divalent ions in alkaline earth chalcogenides are viewed as compressible objects and are treated within a purely ionic model. As in earlier studies on the alkali and ammonium halides, the ions are taken to be in the form of space-filling polyhedral cells and the compression energy, which is the source of repulsion, is written as a surface integral over the cell faces. A simple method of computing the repulsion energy in any crystal lattice of arbitrary symmetry is proposed and the repulsion parametersB andσ are refined for the divalent ions under study. The theory explains the predominant occurrence of the NaCl structure in the alkaline earth chalcogenides. Hard sphere radii are estimated for the tetravalent cations Ti4+, Sn4+ and Pb4+ using the repulsion parameters of O2− ion and the data on the corresponding rutile structure oxides. These radii are seen to be consistent with the measured interionic distances in several compounds occurring in the perovskite structure. The free transfer of repulsion parameters among several structures, which is a key feature of the present approach to repulsion, is confirmed to be valid by the present study.

    • Effect of minute’s-scale aging on refractive index of chopped and non-chopped optical films

      R K Puri K Vijaya R N Karekar

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      The refractive indices of non-chopped and chopped films of cryolite, MgF2 and mixed cryolite-MgF2, which is higher than the bulk value, measured using spectro-photometer, ellipsometer and Abeles method are observed to be higher than corres-ponding bulk values. Chopped films show a higher refractive index than non-chopped films. The electron diffraction study shows a more amorphous structure for the chopped films. The major part played by chop-time seems to be in increasing the initial minute’s-scale aging rather than settling of ad-atoms during chop-time. The observed dispersion curve shows that some unknown material other than water gives an important aging effect.

    • Study of1840Ar ion tracks in cellulose nitrate

      Subhash Chander Shyam Kumar J S Yadav A P Sharma

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      Sample of cellulose nitrate (Russian) is exposed to1840Ar ions. The bulk etch rate has been studied at different etching temperatures and the activation energy for bulk etch rate has been calculated. The etched track lengths are measured for different etching times. The energy loss rate and range of1840Ar ions in CN(R) is also calculated. The critical threshold value for etchable track in CN(R) is determined by comparing the theoretical and experimental values of track length. The response curve of CN(R) is also presented.

    • Mesonic decays of τ lepton: Effects of neutrino mass and mass mixing

      R R L Sharma N K Sharma

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      Experimentally established mesonic decays ofτ lepton have been reexamined with the inclusion of the effects of finite neutrino mass and the associated mass mixing in the form of Kobayashi-Maskawa mixing matrix. A comparison with the experimentally predicted decay probabilities provides limits for thevτ mass which are finite in all decays except for the lower limit in mass mixing case of the decayτK* (892)+vτ for which$$m_{v_\tau } = (420 \pm 610)$$ MeV. The large error in this value is because of (i) large errors in the experimental values of life time and branching ratio for this decay and (ii) thekm mixing used in the calculations. The ratio of parity-violating to parity-conserving terms in the differential decay probabilities of various decays differs slightly from their values corresponding to those with varishingvτ mass.

    • Response of Makrofol polycarbonate plastic track detector to 1.1 MeV/N54132Xe-ion

      S M Farid A P Sharma

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      Makrofol polycarbonate plastic track detectors have been exposed to54132Xe -ions of energy 1.1 MeV/N from the cyclotron beam. The bulk etch rate and track etch rate are measured for different temperatures and the activation energies are calculated. The maximum etched track length is compared with the theoretically computed range. The critical energy loss is (dE/dx)c=5 MeV cm2 mg−1 for this detector material.

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