• Volume 26, Issue 3

      March 1986,   pages  1-281

    • Fibrebundle formalism for supergravity

      G Sardanashvily O Zakharov

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      The non-Poincaré version of supergravity is suggested. This extends the description of gravity as the Higgs-Goldstone type field on supergravity.

    • A radiating Kerr-Newman solution

      L K Patel Sharda S Koppar

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      A non-static exact solution of Einstein’s equations corresponding to a field of flowing null radiation plus an electromagnetic field is presented. The geometry of the solution is described by the Kerr-Schild metric. The solution admits a shear-free, geodetic null congruence. It has the symmetry of the Kerr-Newman solution and when a certain parameter is put equal to zero the solution becomes static and reduces to the Kerr-Newman solution.

    • Correlation between fractional independent yields and neutron-to-proton ratio of fission products in low energy fission

      A Goswami B K Srivastava Alok Srivastava S B Manohar Satya Prakash M V Ramaniah

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      Fractional independent yields of fission products in the thermal neutron-induced fission of233U,235U,239Pu,241Pu and in the spontaneous fission of252Cf have been correlated with the neutron-to-proton ratio of the fission products. The yields of the products from a fissioning system, when plotted as a function of neutron-to-proton (N/Z) ratio of fission preducts, fall on two Gaussian distribution corresponding to light and heavy fission products. The centroids of the distribution or the most probable value of neutron-to-proton ratio is found to be very close to theN/Z of the fissioning nucleus. From the most probable value ofN/Z the various parameters of charge distribution e.g. most probable massAp, most probable chargeZp, the mass dispersionσAand the charge dispersionσZhave been obtained and are in good agreement with the experimental values ofApandZp.

    • Fabrication of lithium-drifted silicon detectors by constant temperature method

      R P Sharma A S Divatia

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      A new approach for lithium drifting in silicon is described where the silicon devices under drift are held at constant temperature and bias at normal air ambient, and the drift process is terminated at the end of an estimated time depending upon the thickness of wafers. A 4-channel lithium drifting unit with electronically controlled oven has been constructed for this purpose. Full details of the fabrication procedure are given. A sizable number of Si(Li) detectors have been fabricated using this approach. The quality of the detectors is tested with241Am alphas and conversion electrons from209Bi and137Cs sources. The detectors are regularly used for nuclear physics experiments at this Centre.

    • Enhancement of spectral intensities of mercury triplet lines in longitudinal magnetic field

      S N Sen S K Sadhya

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      The variation of intensity of the spectral lines of the triplet series of mercury namely (73S1 → 63P012) (λ5461 Å,λ 4358 Å,λ 4047 Å) in the presence of a longitudinal magnetic field between zero and 2000 gauss has been investigated. The effect of magnetic field is found to be different as regards the variation of intensity and the occurrence of maxima in the three lines. These variations can be explained by considering the reabsorption of the spectral lines. A mathematical theory has been presented and an expression for (Iul)B/Iul has been deduced where (Iul)B and (Iul) are the intensities of the lines with and without the magnetic field. The experimental results agree fairly well with the theoretical model.

    • Diffraction from a quasi-crystalline chain

      M C Valsakumar Vijay Kumar

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      We present a general formalism for diffraction from a one-dimensional quasicrystal with arbitrary length scales and sequences. The notion of sub-quasi-lattices is introduced and the effect of different basis on different sites is studied. The relevance of this work for the study of vibrational and electronic spectra of the chain is discussed.

    • Isochoric temperature coefficient of surface tension andSo-parameter of quasi-spherical molecular liquids

      B K Sharma

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      The Sharma parameterSo which is characteristic of molten alkali halides and polymers has also been shown to be characteristic of a wide variety of liquids. Calculated data using the volume expansivity of the liquid establish the constancy of theSo-parameter which retains, on an average, a constant value of 1·11 for quasi-spherical molecular liquids. It is shown thatSo-parameter is also related to volume expansivity of the surface layer of the liquid, temperature coefficient of surface tension of liquids and describes the temperature and volume or pressure dependence of thermodynamic Grüneisen parameter and isochoric heat capacity with significant contribution for influencing the thermoacoustic and surface tension properties of liquids.

    • Unified study of lead: Energy-dependent pseudopotential calculation

      A Sarkar D Sen S Sengupta

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      A Unified study of lattice-mechanical properties of lead using energy-dependent pseudopotential is carried out. Energy dependence in pseudopotential is considered through the effective mass approximation; the pseudopotential model chosen is the local Heine-Abarenkov model potential. Properties studied include cohesive energy, equilibrium lattice parameter, second-order elastic constants, pressure derivative of second-order elastic constants, equation of state (atT=0 K), phonon-dispersion and effective two-body interaction. The results show fairly good agreement with experiment especially with a modified Heine-Abarenkov potential.

    • Theory of two-phonon modes in layered charge-density-wave systems

      S N Behera G C Mohanty

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      A theoretical model with electron-phonon and anharmonic interactions is proposed to explain the two-phonon mode observed in the Raman spectra of layered transition metal dichalcogenides, which exhibit charge density wave (cdw) phase transition. The phonon self-energy, which involves the electron response function and the two-phonon Green’s function, is calculated using the double-time Green’s function formalism. It is shown that in these low-dimensional systems there exists an anharmonicity-mediated two-phonon mode in the phonon spectral function both in the normal and in thecdw phases. In the normal phase since the phonon Raman scattering proceeds through a single optic phonon the calculations are carried out for zero wave vector and hence the contribution of the electron response function to the self-energy vanishes. On the other hand explicit evaluation of the two-phonon Green’s function shows that the frequency of the two-phonon mode is twice that of the Kohn anomaly phonon and decreases with decreasing temperature. The strength of two-phonon peak is found to be comparable to that of the original optic phonon. In thecdw phase the phonon which enters into the Raman scattering is taken to be the one with thecdw wave vectorQ, which when zone-folded becomes equivalent to zero wave vector. The evaluation of the electron response function in this phase generates a phonon corresponding to thecdw-amplitude mode. The two-phonon Green’s function is assumed to be of similar form as in the normal phase. The spectral function evaluated at zero temperature shows a weak two-phonon peak besides the prominentcdw-amplitude mode. Numerical results are presented for the system 2H-NbSe2 and are found to be in qualitative agreement with the experimental data.

    • Proton magnetic relaxation in (TMA)2HgBr4 and (TMA)2HgI4

      B S Sarma J Ramakrishna

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      Internal motions of the protonic groups have been studied in polycrystalline [(CH3)4N]2HgBr4 and [(CH3)4N]2HgI4 from the temperature dependence of proton spin relaxation time (T1) and the data analysed according to the spin lattice relaxation model due to Albert and coworkers. The temperature dependence ofT1 in the above compounds is compared with that in (TMA)2HgCl4 and (TMA)2ZnCl4.

    • Optical absorption and electrical conductivity of flash evaporated CuGaTe2 thin films

      K V Reddy J L Annapurna

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      The optical absorption edge of CuGaTe2 thin films in the energy range 1 to 2·3 eV was studied. The characteristic band gaps were found to be 1·23 eV and 1·28 eV whereas the acceptor ionization energy was 170 meV. Electrical conductivity measurements were carried out in the temperature range 300–550 K and two acceptor states with ionization energies 400 meV and 140 meV were found. The origin of acceptor states is explained based on covalent model.

    • Photocurrent characteristics in Cu2O/Pt and Cu2O/TiO2 photoelectrochemical cells in aqueous and non-aqueous electrolytes

      K A Khan J F Kos

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      Photocurrent characteristics of the Cu2O/Pt and Cu2O/TiO2 photoelectro-chemical cells have been presented. In aqueous solution, a slow deterioration of power output occurs approximately at the rate of 50% per day. Operation in non-aqueous solutions (acetonitrile and ethanol) also produced a deterioration of power output. However in ethanol, it was found that the deterioration reversed itself and a new cycle of deterioration and rejuvenation began. These suggest that the deterioration is not due to a chemical reduction process at the electrode surface but other factors such as migration of charged defect centres in the depletion layer or chemical reaction on the electrode surface.

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