• Volume 10, Issue 5

      May 1978,   pages  453-550

    • Effect of correlations on electron momentum density in liquid metals

      P Chaddah

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      A scheme to calculate the electron momentum density in simple liquid metals, with the effect ofboth electron correlations and ionic potentials included, is given. This scheme is applied to the case of liquid aluminium. The results are substantially different from calculations considering only the ion potentials, and also from the results for a homogeneous electron gas of corresponding density.

    • Absorption and laser excited fluorescence of Ho3+:LaF3

      Bansi Lal D Ramachandra Rao

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      The absorption and fluorescence spectra of Ho3+:LaF3, in the wavelength region from 4000 Å to 7500 Å have been reinvestigated incorporating polarization features, for the first time. The fluorescence spectrum, recorded using a spectrophotometer assembled in the laboratory, was excited with a He-Ne laser and an Ar+ laser. The present study enabled the interpretation of the data in terms of theC2v site symmetry of Ho3+ and most of the Stark components of the observed states have been classified under the irreducible representations of theC2v point group.

    • Photoelectric properties of pure and aluminium doped CdS films

      S Jatar A C Rastogi V G Bhide

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      Photoelectric properties of pure and Al doped vacuum deposited CdS films have been studied to explore the possibility of their application in photoactivated liquid crystal light valves. The effect of heat treatment in oxygen atmosphere, rate of deposition and the extent of Al doping, etc. on the resistivity, photo-response spectral characteristics, rise and decay time of photo-current, etc. have been investigated. It has been found that in contrast to pure CdS films, the properties of Al-doped films significantly depend on both the rate of deposition and the extent of Al doping. The dark resistivity in all cases was found to increase with heat treatment in oxygen. Unlike pure CdS films, Al doped films show photo-conductivity which is enhanced by heat treatment. Al doped films deposited at higher rates show better photo response even at lower light levels. At various light levels the rise and decay time of Al-doped films were found to be fairly constant and lower than that for pure CdS films. All these properties have been explained in terms of the presence of trapping levels due to doping. These trapping levels are also indicated by TSC, optical absorption and EPR studies.

    • Effect of pressure on F-band energies in alkali halides

      Nawab Singh A W Joshi

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      Variation of peak F-band absorption energy and lattice distortion with pressure has been calculated for lithium halides employing extended ion model and using values of local compressibility in the neighbourhood of the F-centres which include the effect of vacancy and pressure. The calculated results are in very good agreement with experimental results.

    • Computer simulation of back sputtering and ion penetration into polycrystalline targets

      R Shanta

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      In the present work computer simultations of the back sputtering of low energy neon ions with low impact parameter and the penetration of the same for higher values of the impact parameter have been performed. Initial ion energies in the range 100 to 500 eV and impact parameters in the range 0<p⩽0.61 Å have been used. Assuming a binary collision model and for the interatomic potential the Leibfried-Oen matching potential, we compute the complete collision cascade. For Ne+-Cu interaction, the sputtering threshold energy is found to be 125 eV and the sputtering yield increases with the ion energy. The sputtering yield versus ion energy is plotted and is found to agree well with experiment. It is seen that the back scattering is confined to small impact parameters justifying the use of the binary collision model.

    • Domain formation inside thick crystals of ferroelectric PbNb2O6

      S G Ingle B M Bangre

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      Stress dependence of domains in thick crystals of PbNb2O6 is reported. Successive etching shows numerous domains in the bulk not extending to the surface. These domains have correlation with the dislocation substructure in the bulk. The dislocations are in the form of small loops, and domain walls are found terminating along with these loops. The general problem of volume nucleation is discussed, and it is suggested that these dislocation loops play a significant role in domain formation.

    • Measurement ofL-shell photoelectric cross sections in highZ elements at 60 keV

      K L Allawadhi S K Arora B S Sood

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      L-shell photoelectric cross sections have been measured at 60 keV for six elements in the range 74≤Z≤92. The measurements are found to agree with theoretical calculations.

    • Rotational analysis of the 0–9, 0–10 and 0–11 bands of theA2IIu-X2IIg band system of (16O18O)+

      G L Bhale N A Narasimham

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      High-resolution spectra of the 0–9, 0–10 and 0–11 bands of theA2IIuX2IIg system of (16O18O)+ ion have been studied for their rotational structure. This study enables a direct determination of the Λ-doubling parameters of theA2IIu andX2IIg states. The model of ‘pure precession’ explains, though not entirely, the Λ-doubling of theX2IIa state as arising out of its interaction with theB2Σg state. The Λ-doubling in theA2IIu state was found insignificant.

    • Nuclear matter test for a separable non-localN-N interaction

      M L Sharma Lal Singh

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      A nuclear matter test has been conducted on a separable non-localN-N interaction proposed by Sirohi and Srivastava. The potential had been constructed by fitting the phase-shifts. The results obtained compare with those obtained by Tabakin in each partial wave. The binding energy per particle and the symmetry energy coefficient obtained are 19.4 MeV and 66.5 MeV respectively atkF=1.65 fm−1, while the best estimated values for these quantities are 16 MeV and 30–35 MeV atkF=1.5 fm−1. Single particle potential generated out of this NLSI has in general the same shape as the one obtained through Tabakin potential. Finally as a test of non-locality the integrated photoabsorption cross-section parameterh has been calculated and the value of 1.03 agrees with other reported values.

    • Partially conserved axial-vector current inS-matrix theory

      J Pasupathy C A Singh

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      Mandelstam’s argument that PCAC follows from assigning Lorentz quantum numberM=1 to the massless pion is examined in the context of multiparticle dual resonance model. We construct a factorisable dual model for pions which is formulated operatorially on the harmonic oscillator Fock space along the lines of Neveu-Schwarz model. The model has bothmπ andmϱ as arbitrary parameters unconstrained by the duality requirement. Adler self-consistency condition is satisfied if and only if the conditionmϱ2mπ2=1/2 is imposed, in which case the model reduces to the chiral dual pion model of Neveu and Thorn, and Schwarz. The Lorentz quantum number of the pion in the dual model is shown to beM=0.

    • Dipionic decays of psions in a local derivative coupling model

      B Bagchi V P Gautam A Nandy

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      A local derivative coupling model is used to study theφ′→ππ and other dipionic decays ofφ andφ″, as an alternative to theε-model. The results obtained are quite satisfactory. We findt hat the existence of theε-resonance is not essential in order to understand the dipionic decays of the psions at the present level of experimental data available.

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