• R V Nandedkar

      Articles written in Pramana – Journal of Physics

    • Lattice dynamics of beryllium

      B A Dasannacharya P K Iyengar R V Nandedkar K R Rao A P Roy C L Thaper

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      Phonon frequencies in beryllium along the principal symmetry directions have been determined by means of the slow neutron inelastic scattering technique. The data are analysed in terms of a six-neighbour force constant model and the force constants are evaluated. It is concluded that strong tensor forces are present in beryllium and the importance of this finding to basic theories of lattice dynamics is pointed out.

    • Effect of irradiation at low doses and incubation of voids within the rate theory approach

      K Krishan R V Nandedkar

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      The evolution of defects in a material under irradiation is studied at low doses (∼5 dpa or less) using rate equations. It is shown that as a function of temperature at a critical valueTc a transition occurs in the behaviour of the solutions of the rate equations. BelowTc the voids show incubation effects. An expression is derived for the critical dislocation density at which the void growth starts. This is related to the trapped vacancy fraction ε in vacancy dislocation loops. AboveTc the incubation effects are shown to be related to the gas production rate which becomes the rate controlling parameter in determining the evolution of the defects. A gas-bubble to void transition occurs at a critical void radius and expressions are derived for the critical void size and dose at which the transition appears. It is shown that closely related to this is the incubation dose for interstitial loops. Finally, these features are corroborated by actual numerical integration of the rate equations.

    • 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.

    • Optical design of a toroidal grating monochromator based beam line on Indus-1

      K J S Sawhney R V Nandedkar

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      In this paper, we discuss the detailed optical design of a beam line that is under construction on the synchrotron radiation source, Indus-1. Toroidal mirrors are used as pre-and post- focusing elements and a toroidal grating monochromator as a dispersing element. Using three interchangeable gratings, this monochromator will give, at a moderate resolution, a good throughput on the sample in the wavelength range 40 to 1000 Å. Effect of various parameters and their optimization on the resolution and throughput characteristics have been studied by ray tracing calculations, and presented.

    • Use of spherical gratings in a toroidal grating mount for vuv-soft x-ray synchrotron radiation

      K J S Sawhney A I Munshi R V Nandedkar

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      A toroidal grating monochromator (TGM) based beamline was designed earlier and it is being setup on the 450 MeV Indus-1 synchrotron radiation source. This beamline operates in 40–1000 Å wavelength range and gives a moderate resolution (∼500) at high throughput. Now-a-days, spherical gratings are giving very high resolution in some complex monochromators. We have evaluated the use of spherical gratings in the simple rotation mount of a TGM. The motivation has been to evaluate if the existing TGM beamline, without any hardware changes, can be used with the much cheaper spherical gratings. The two monochromators, employing toroidal and spherical gratings respectively, have been compared by performing detailed ray tracing calculations. Our study shows that, with the same mechanical hardware, a real spherical grating monochromator gives better performance compared to the conventional TGM with respect to the spectral resolution and the flux. Furthermore, for moderate resolution this improvement is realized even when the exit slit is not moved to keep the spherical grating in-focus.

    • Synchrotron radiation sources INDUS-1 and INDUS-2

      D D Bhawalkar G Singh R V Nandedkar

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      The synchrotron radiation sources, INDUS-1 and INDUS-2 are electron storage rings of 450 MeV and 2 GeV beam energies respectively. INDUS-1 is designed to produce VUV radiation whereas INDUS-2 will be mainly used to produce x-rays. INDUS-1 is presently undergoing commissioning whereas INDUS-2 is under construction. Both these rings have a common injector system comprising of a microtron and a synchrotron. Basic design features of these sources and their injector system are discussed in this paper. The radiation beamlines to be set up on these sources are also described.

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