• Volume 19, Issue 6

      December 1982,   pages  525-663

    • Neutrino backgrounds in the Kolar Gold Field nucleon decay experiment

      M R Krishnaswamy M G K Menon N K Mondal V S Narasimham B V Sreekantan Y Hayashi N Ito S Kawakami S Miyake

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      The neutrino events recorded in the Kolar Gold Field Nucleon Decay detector are analysed here. It is shown that there is good agreement between the observations and the estimates based on the intensities of atmospheric neutrinos and interaction cross-sections of neutrinos available from accelerator experiments. In the context of the search for proton decay, we show that the low energy (<2 GeV) neutrino events, which would provide the main background, are suppressed at thekgf site since it is situated near geomagnetic equator, where the geomagnetic cut-off rigidities are high. A comparison of the predicted characteristics ofv-induced events with thekgf observations shows that, within the statistical accuracy of the present data, the signal due to nucleon decay stands out distinctly within thev-induced background.

    • Mass formulae for Λ-hypernuclei

      Kamales Kar Jitendra C Parikh

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      Simple considerations regarding the Hamiltonian and the ground state wavefunctions of Λ-hypernuclei are used to derive several mass formulae. The parameters that occur in the mass formulae are determined by fitting the experimental binding energies. Information regarding the various interactions in hypernuclal is deduced from the values of these parameters. The ‘best’ mass formula is further used to predict energies of other light hypernuclei. Relationship between binding energies are also suggested and checked with observed data.

    • Reaction48Ca (p, n)48Sc fromEp=1.885 to 5.1 MeV

      Gulzar Singh S Kailas S Saini A Chatterjee M Balakrishnan M K Mehta

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      The total (p, n) reaction cross section for48Ca has been measured as a function of proton energy in the energy range 1.885 to 5.100 MeV with an overall resolution of ∼ 2 keV and in ∼ 5 keV energy steps. The fluctutions in fine resolution data have been analysed to determine the average coherence width 〈Γ〉. The excitation function averaged over large energy intervals has been analyzed in terms of the optical model. The isobaric analogue resonances atEp ∼ 1.95 and 4 MeV have been shape-analyzed to extract the proton partial width and the spectroscopic factorSn. A comparison of the gross structures observed in ∼ 55 keV averaged excitation function with the predictions of Izumo’s partial equilibrium model has also been made.

    • Electret microphone for use in photoacoustic spectrometer and photoacoustic spectrum of some rare earth oxide powders

      V N Rai L B Tiwari S N Thakur D K Rai

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      We describe a new method for the polarization of an electret foil which has proved very convenient and yields a foil having very good performance in a microphone. The variations in the charge accumulation on the electret foil and its decay with time as well as the variation of the microphone sensitivity with different microphone parameterse.g. different thicknesses of the electret foil, different back plates and different polarization techniques has been investigated. The sensitivity of the home-made microphone is estimated as 1 mV/μbar. The working of this type of microphone and its comparison with a commercial microphone as used in a (laboratory made) single beam photoacoustic spectrometer is discussed.

      A brief description of the photoacoustic spectrometer including microphone biasing and the photoacoustic cell is given. The photoacoustic spectra of some rare earth oxides in the form of powders have been recorded. It is seen that the atomic levels of triplyionized rare earths which are not fluorescent appear very prominently in the photoacoustic spectrum. The spectra for terbium and praseodymium oxides do not show clear peaks probably due to the presence of different stoichiometric forms.

    • Neutron, x-ray and lattice dynamical studies of paraelectric Sb2S3

      K R Rao S L Chaplot V M Padmanabhan P R Vijayaraghavan

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      Neutron and x-ray diffraction studies of Sb2S3 indicate extensive diffuse scattering in the plane perpendicular to the chain axis of polymer-like (Sb4S6)n molecules. The crystal structure of the paraelectric phase is said to be orthorhombic with space group D2h16 with four molecules per unit cell. The observed diffuse scattering may be due to static disorder or some dynamical effects. In this paper the authors have examined the possible dynamical origin by recourse to lattice dynamical studies. Dispersion relation of phonons along the three symmetry directionsa*,b* andc* is evaluated based on a lattice dynamical model incorporating Coulomb, covalent and a Born-Mayer-like short range interactions. Group theoretical analysis based on the group of neutral elements of crystal sites (GNES) was essential in order to examine and aid in the numerical computations. The group theoretical technique involving GNES extended to ‘pseudo-molecular’ systems is also discussed in this context.

      The phonon dispersion relation shows that there are rather flat TA-TO branches of very low frequency in thea andc directions which may give rise to diffuse scattering. The branches along theb-axis are quite dissimilar to those alonga andc axes because of anisotropy. Variation of the potential parameters leads to instability of the lowest TA-TO branch. This is suggestive of a temperatures or pressure-dependent phase transition. However since these modes are optically ‘silent’ one needs to carry out either high resolution neutron scattering or ultrasonic studies to confirm various aspects of the theoretical studies.

    • A stochastic theory for clustering of quenched-in vacancies-V. Temperature dependence of cluster density

      G Ananthakrishna

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      It is known that the density of vacancy loops in quenched aluminium and stacking fault tetrahedra in quenched gold show a saturation for low ageing temperatures. The physical mechanism leading to this effect is not well understood. In this paper we consider a simple model which allows us to obtain the temperature dependence of total density. The analysis shows that the plateau region arises due to the fact that the number of absorption sites of a cluster is larger than the number of emission sites. The temperature dependence of the average number of vacancies in a cluster and the single vacancy concentration in equilibrium with the clusters are discussed.

    • Effect of non-magnetic impurities on the observation of superconducting gap excitations by raman scattering

      G C Mohanty S N Behera

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      The effect of small concentrations of non-magnetic substitutional impurities (characterized by changes in mass, nearest neighbour force constants and local electron-phonon interaction) on the observability of superconducing (sc) gap excitations in 2H-NbSe2 by Raman scattering is considered within the theoretical framework of Balseiro and Falicov (bf). The phonon self-energy when evaluated forq=0 using the Einstein oscillator model for the host phonons is seen to have a pole corresponding to the impurity mode besides the gap excitation one around 2Δ previously obtained bybf. A splitting of the impurity mode into two in thesc state is predicted. An enhancement occurs in the strength of thesc gap excitation peak whenever it is close to the impurity mode. The data from the experiments of Sooryakumar, Klein and Frindt on impure samples of 2H-NbSe2 are discussed in the light of the present calculation.

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