• Volume 52, Issue 5

      May 1999,   pages  1-528

    • Solar neutrino oscillation diagnostics at SuperKamiokande and Sudbury Neutrino Observatory

      Debasish Majumdar Amitava Raychaudhuri

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      Results for solar neutrino detection from the SuperKamiokande collaboration have been presented recently while those from the Sudbury Neutrino Observatory are expected in the near future. These experiments are sensitive to the8B neutrinos from the sun, the shape of whose spectrum is well-known but the normalization is less certain. We propose several variables, insensitive to the absolute flux of the incident beam, which probe the shape of the observed spectrum and can sensitively signal neutrino oscillations. They provide methods to extract the neutrino mixing angle and mass splitting from the data and also to distinguish oscillation to sequential neutrinos from those to a sterile neutrino.

    • Partial quantum recurrence in free and quasibound systems

      A K Sikri M L Narchal

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      The quantum motion of a periodically two-sided kicked free particle is studied under various boundary conditions. The quasienergies, quasistates and the energy of the system are determined exactly. It is found that the energy of the system recurs irrespective of boundary conditions whereas the wave function shows recurrence only for a completely bound particle.

    • Some new four-parameter potentials and their use in the study of vibrational thermodynamical quantities of diatomic molecules

      Sarvpreet Kaur C G Mahajan

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      Three four-parameter potentials,UI,UII andUIII have been proposed and their accuracy has been demonstrated by finding the mean square deviation from the true RKR potential curve for 15 electronic states of 12 diatomic molecules. Their percentage average mean square deviations from RKR curve have been found to be 1.45, 1.86 and 2.89, respectively. These compare favourably with the value 2.67 for the recently suggested four-parameter potential of Wei Hua which itself yields better results than the commonly employed three-parameter potentials. The superiority of the new potentials (especially ofUI andUII has been further established by using these potentials to calculate the molecular constants αe and ωexe following Dunham’s method. The corresponding percentage average mean deviations, for αe, turn out to be 3.75, 5.13 and 15.43 and for ωexe 8.73, 17.23 and 27.49, respectively, against the respective values of 7.97 and 18.88 with Wei Hua’s four-parameter potential. Also included are the values of dissociation energy determined with these potentials and these too corroborate the better performance ofUI andUII. The relative worth of various potential functions has been further tested by carrying out numerical study of vibrational partition function (evaluated by sum over states method), entropy and thermal capacity for the ground state of 7 molecules and comparing these with the corresponding findings based on the RKR data.

    • Angular anisotropy and dichroism in molecular Auger spectroscopy following photo-absorption

      M Chakraborty

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      This paper shows that angular distribution of spin-unresolved Auger electrons emitted in the decay of a vacancy created by the absorption of a photon in a certain class of free, unpolarized and gaseous non-linear molecules is completely characterized by three, rather than by two well-known parameters. The presence of this additional third parameter gives rise to circular dichroic effect which varies as cosine of the angle made by the departing Auger electron with the direction of incidence of the circularly polarized radiation. Linear dichroic effect varies as the square of sine of the angle made by the direction of emission of Auger electron and the polar axis of the space frame. Linear and circular dichroism in the angular correlation between theE1 photoelectron and Auger electron emitted sequentially from a molecule belonging to one of the 32 point groups has also been investigated.

    • Thick-target X-ray bremsstrahlung spectra produced in 6.5 keV and 7.5 keVe--Hf collisions

      S K Goel R Hippler Rajesh Kumar Singh R Shanker

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      The absolute doubly differential cross-sections (DDCS) for production of the thick-target X-ray bremsstrahlung spectra in collisions of 6.5 keV and 7.5 keV electrons with thick Hf target are measured. The X-ray photons are counted by a Si(Li) detector placed at 90° to the electron beam direction. The bremsstrahlung spectra are corrected for various ‘solid-state effects’ namely, electron energy-loss, electron back-scattering, and photon-attenuation in the target, in addition to the correction for detector’s efficiency. The DDCS values after correction, are compared with the predictions of a most accurate thin-target bremsstrahlung theory [H K Tseng and R H Pratt,Phys. Rev.A3, 100 (1971); Kisselet al, Atomic Data Nucl. Data Tables28, 381 (1983)]. Also, a dependence of the absolute DDCS on atomic numberZ of the targets (47Ag,79Au and72Hf) at 7.0 keV and 7.5 keV electron energies has been studied. The agreement between experiment and theory is found to be satisfactory within 27% systematic error of measurements. However, an apparent systematic difference between experiment and theory in the region of low-energy photons has been explained qualitatively by considering the fact that the hexagonal atomic structure of Hf offers possibly a greater magnitude of ‘solid-state effects’ in respect of blocking the low-energy bremsstrahlung photons from coming out of the target surface than does the cubic-face centered structure of Ag and Au target in similar conditions of the experiment.

    • Debye-Waller factors and Debye temperatures of alkali halide mixed crystals

      P Geeta Krishna K G Subhadra T Kumara Swamy D B Sirdeshmukh

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      The Debye-Waller factors of KxRb(1-x)I and NaClxBr(1-x) mixed crystals have been determined from X-ray diffraction intensities. The mean Debye-Waller factor is found to vary nonlinearly with the composition with positive deviations from linearity. The Debye temperatures (calculated from the Debye-Waller factors) are found to vary slightly non-linearly with composition with negative deviations from linearity. The Debye temperatures of seven alkali halide mixed crystal systems are critically compared with values predicted from six laws for composition variation. Using the estimated standard deviation as the criterion for the goodness of the fit, it is shown that the inverse cube (Kopp-Neumann) law provides the best description for the composition dependence of Debye temperatures of mixed crystals.

    • Theoretical study of structural energy, phonon spectra, and elastic constants of Rh and Ir

      N Singh

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      The transition metal pair potential (TMPP) is used to study band structure energy of Rh and Ir. Both metals are found to be most stable in fcc structure down to atomic volume 0.5V0. The pressure at 0.5V0 is found to be 5.235 Mbar and 9.216 Mbar in Rh and Ir, respectively. The TMPP is also used to study other properties of these metals like cohesive energy, phonon frequencies at observed volume. The bulk moduli and elastic constants of these metals at observed volume are calculated by including the volume contribution.

    • Photoacoustic cell with black absorber as a detector for spectrophotometric studies

      A R Dhobale M D Sastry

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      The PAS cell with carbon black absorber is used as a detector for spectrophotometry in an open room. This has immense potential of obtaining absorption speciation information from remote samples.

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