• Volume 39, Issue 2

      August 1992,   pages  95-191

    • Search for the effect of pressure on liquid-liquid critical phenomena

      A Kumar V C Vani A G Aizpiri R G Rubio

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      The coexistence curve of methanol + cyclohexane has been reanalyzed using an intrinsically simpler equation to study the influence of pressure on its asymmetry. The results confirm that no pressure dependence is discernible in the coexistence curve. Suggestions for future work in this direction are made.

    • Anharmonic oxygen vibration and mode softening in Tl2Ba2Ca2Cu3O10 superconductor

      Nabonita Deb Chowdhury Sankar P Sanyal

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      The softening of the IR active 300 cm−1 phonon mode in Tl-2223 superconductor, aroundTc has been explained by considering a sixth order polarization potential at the off-center oxygen ion site in the Tl-O plane, and by using a nonlinear lattice dynamical theory. The present theory explains, more or less satisfactorily, the unusual temperature dependence of oxygen ion vibration and frequency shifts at higher temperature. The existence of strong nonlinear electron-phonon interaction atTc has been emphasized.

    • Thermal conductivity of YBa2Cu3O7 from 7 K to 260 K

      T R Ravindran V Sankaranarayanan R Srinivasan

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      Thermal conductivity of YBa2Cu3O7 has been measured on samples of a few mm thickness. AboveTc thermal conductivity is found to decrease with increase in temperature, pointing towards a contribution to thermal resistivity from three-phonon Umklapp processes. BelowTc thermal conductivity increases rapidly before reaching a maximum at about 50 K and then falls towards zero at lower temperatures. The experimental set up is described and results discussed.

    • Solid state effects during deuterium implantation into copper and titanium

      H K Sahu M C Valsakumar B Panigrahi K G M Nair K Krishan

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      Results of neutron counting experiments during deuterium implantation into titanium and copper are reported. Models for neutron yield have been developed by taking into account different solid state effects like energy degradation of incident ions, energy dependent d-d fusion cross section and diffusion of implanted deuterium possibly influenced by surface desorption and formation of metal deuterides. The asymptotic time dependence of the neutron yield during implantation has been compared with the experimental results. Using these results, solid state processes that might occur during deuterium implantation into these metals are inferred.

    • Thermally stimulated luminescence and electron paramagnetic resonance studies of actinide doped calcium chloro phosphate

      T K Seshagiri V Natarajan M D Sastry

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      Electron paramagnetic resonance [EPR] and thermally stimulated luminescence [TSL] studies were conducted on self [α]-irradiated239Pu doped calcium chloro phosphate andγ-irradiated239Pu/238UO22+ doped calcium chloro phosphate to elucidate the role of the electron/hole traps in thermally stimulated reactions and to obtain trap parameters from both TSL and EPR data. TSL glow peaks around 135 K (# peak 1), 190 K (# peak 2), 435 K (# peak 5) and 490 K (# peak 7) were observed and their spectral characteristics have shown that Pu3+ and UO66− act as luminescent centres in calcium chloro phosphate with respective dopants. EPR studies have shown the formation of the radical ions H0, PO42−, O, O2 and [ClO]2− under different conditions. Whereas the [ClO]2− radical being stable up to 700 K, was not found to have any role in TSL processes, the thermal destruction of other centres was found to be primarily responsible for the TSL peaks observed. The trap depth values were determined both by using the TSL data and also the temperature variation of EPR spectra of these centres.

    • Photoconductivity and dark conductivity studies of (MgO-ZnO) mixed system

      Sadhana Devi S G Prakash

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      The photoconductivity and dark conductivity of (20% MgO-80% ZnO) mixed system in polystyrene binder layer have been studied and compared with (50% MgO-50% ZnO) and ZnO samples. For (20% MgO-80% ZnO) and (50% MgO-50% ZnO) samples, the dark current is found to be space charge limited at higher voltages. The photocurrent shows non-Ohmic behaviour at lower voltages and tends to saturation at higher voltages. For 100% ZnO system at higher voltages the photocurrent does not show any saturation effect and the dark current becomes linear. The change in photocurrent versus intensity curve from superlinear to sublinear indicates the presence of sensitizing centres near to the valence band and the existence of an exponential trap distribution in (20% MgO-80% ZnO) and (50% MgO-50% ZnO) samples. For 100% ZnO system, the photocurrent versus intensity curve changes from sublinear to linear indicating the presence of exponential trap distribution. Photocurrent decays more rapidly with increasing percentage of MgO in the mixed system. The X-ray diffraction pattern of these samples do not show formation of solid solutions.

    • Surface enhanced Raman scattering of 2-cyanopyridine adsorbed on silver colloidal particles

      Ekram Ali Shaikh Y Kumar B N Khanna

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      Surface-enhanced Raman scattering (SERS) spectra of 2-cyanopyridine (2 CP) adsorbed on silver colloidal particles have been investigated. The prominent SERS bands are observed at 556, 612, 778, 1002, 1060, 1072, 1150 and 1240 cm−1. The absolute enhancement factor of the Raman signals in SERS studies has been estimated to be of the order of 102–105 for various bands. The 2CP molecules have been ascribed to adsorb on colloidal particles in standing up fashion.

    • The inductively coupled plasma spectrum of OD in the infrared

      Mark C Abrams Sumner P Davis M L P Rao Rolf Engleman

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      To gain more information about the highly excited rotational states of the Δv = 1 sequence of OD vibration-rotation bands, the spectrum has been produced in an inductively coupled plasma discharge and measured with a Fourier transform spectrometer between 1670 and 5768 cm−1. Along with the extension of 1–0 band, we have been successful in recording the 2–1 band for the first time. A nonlinear least square fit of these bands yielded equilibrium molecular parameters forv = 0, 1 and 2 levels with a standard deviation of 0·0032 cm−1. The centrifugal distortion parameters show a systematic vibrational dependence.

    • Imaging characteristics of toroidal and ellipsoidal mirrors for synchrotron radiation source Indus-1

      K J S Sawhney R V Nandedkar

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      We discuss and compare the imaging characteristics of toroidal and ellipsoidal mirrors for different horizontal acceptances of synchrotron radiation source Indus-1; using a ray tracing method. It has been shown that the toroidal and ellipsoidal mirrors have similar focussing behaviour at small horizontal acceptances. For large horizontal acceptances, toroidal mirror shows an asymmetry in the focussed image. Though the data used here are for Indus-1, the results are generally valid for any bending magnet synchrotron radiation source incident at grazing angles on these mirrors.

    • Ultra lowqa discharge experiments in the SINP tokamak

      A N Sekar Iyengar S K Majumdar J Basu R K Paul R Pal S Chowdhury

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      Operation of most tokamaks in limited byqa, the edge safety factor, which is usually about 2–3. In the SINP tokamak we have been able to obtain discharges withqa values as low as 0·8. In this paper we describe our results on the setting up processes and the MHD activity associated with these ultra lowqa discharges.

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