Volume 32, Issue 5
May 1989, pages 1-692
pp 1- May 1989 Rapid Communications
Cu K-absorption edges of YBa2Cu3O6.9, Tl2CaBa2Cu2O8 and Bi2CaSr2Cu2O8 show similar features. Copper is mainly in the 2+ state in these cuprates suggesting the likely presence of oxygen holes.
pp 605-618 May 1989 Nuclear Physics
Excitation functions for the reactions121Sb(α, xn)125−xI,123Sb(α, xn)127−xI and121Sb(α, p3n)121Te were obtained from the measurements of the residual activity of stacked foils of antimony trioxide evaporated on Al backings from threshold to 60 MeV. The excitation functions for the production of121I,123I,124I,126I and121Te are presented. The experimental data are compared with calculations considering equilibrium as well as pre-equilibrium reaction mechanism according to the hybrid model of Blann. The high energy part of the excitation functions are dominated by the pre-equilibrium reaction mechanism. Calculations were done using a priori calculational method of Overlaid Alice Code of Blann. Most of the excitation functions in the energy range mentioned above could very well be fitted with the hybrid model calculation for exciton numbern=4 withnn=2 andnp=2. The overall agreement with the theory is good. Certain discrepancies for example121Sb(α, p3n)121Te excitation function, indicate that the production mechanism is different from the one presumed for the calculation.
pp 619-625 May 1989 Plasma Physics
The dispersion relation of electromagnetic waves in the presence of magnetic monopoles of electron mass in a uniform magnetic field is obtained. The waves of the frequencyω in the range ωϱi<Ωi<ω<Ωe<ωϱa are analysed. It is shown that the monopole charges lead to observable effects. Finally, the results are applied to a typical pulsar.
pp 627-639 May 1989 Plasma Physics
Optical emission spectroscopic studies were carried out to characterise the plasma leading to the estimation of two plasma parameters, electron density and temperature. These experiments were conducted on a 2 kJ plasma device which is equipped with squirrel cage electrode configuration enclosed in a glass vacuum chamber filled with hydrogen at a pressure of 5 mbar. Spectral emissions obtained from each flash were photographed in the region of 4000–6000 Å using one metre Czerny-Turner spectrograph cum monochromator. Detailed examination of the observed features showed that theHβ andHλ lines of hydrogen showed significant broadening of the order of 35 Å FWHM which is due to Stark effect expected in high density plasmas. Further several atomic lines of Cu and Zn from the electrode material (brass) showed broadening which was due to quadratic Stark effect. A comparative study of the broadening of lines obtained in DC arc, hollow cathode and plasma focus was made. Electron density from Stark broadened hydrogen lines and quadratic Stark Coefficient C4 for the CuI and ZnI lines were evaluated. The excitation temperature was determined from the line intensity ratio method using CuI lines.
pp 641-646 May 1989 Condensed Matter Physics
Laser Raman spectroscopy was employed as a non-destructive probe for the detection and monitoring of crystalline arsenic in the native oxide films formed during heating of GaAs in air at various temperatures. Spectroscopy of oxide films formed after successive heating and etching treatments could confirm the location of arsenic to be near the top of the GaAs: native oxide overlayer.
pp 647-692 May 1989 Review Paper
The subject of spectral distribution methods where one derives and applies the locally smoothed forms of observables in nuclei is briefly reviewed. It is well understood that the local forms (with respect to energy) of the level density function, expectation values and strength densities are Gaussian, linear (or ratio of Gaussians) and a bivariate Gaussian respectively. To accomodate symmetries in the above forms, one has to deal with multivariate distributions in general; for example the angular-momentum (J) decomposition leads to a bivariate Gaussian form for the level density. These results extend to indefinitely large spaces by method of partitioning and they generate convolution forms. The origin of these remarkable spectral properties is discussed and shell model examples are given to substantiate their applicability to nuclear systems. Spectral distribution theory is a practical, usable theory because the smoothed forms are defined in terms of traces of low particle-rank operators, and the trace information propagates. Finally we discuss the application of the spectral methods for a wide range of nuclear problems; these include binding energies, orbit occupancies, electromagnetic andβ-decay sum rule quantities, analysis of operators, symmetry breaking, numerical level densities, and determination of bounds on time-reversal non-invariant part of nucleon-nucleon interaction.
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