• V N Bhoraskar

      Articles written in Pramana – Journal of Physics

    • Improved resonance in microtrons by orbit shaping

      V B Asgekar R K Bhalla M R Bhiday V N Bhoraskar B S Raye

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      Microtron electron accelerators generally show a 50% reduction of the injected beam in the first orbits. A modification of the race-track magnet system is proposed in this paper to reduce the beam losses. Calculations of the phases of electrons at the microwave cavity yield exact shapes of different orbits required for resonance in a split magnet system. Introduction of small sector magnets in the field-free space provides a feasible method for obtaining the calculated orbit shapes.

    • Surface plasmon dispersion relation for spherical metal particles

      Satish B Ogale V N Bhoraskar P V Panat

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      Using the hydrodynamical model, we have obtained the surface plasmon dispersion relation for spherical metallic particles in the following two cases: (1) a sharp surface cut off in electron density and (2) a diffused electron density at the surface. The diffused density is modelled with a step function. The diffuse nature of the electron density at surface of the metal particle is necessary to understand the experimental result for particles with small radii. Shift in the absorption frequency is estimated and found to be small.

    • A modified electron bombardment type ion source for the study of solids

      S V Ghaisas S M Chaudhari M R Bhiday V N Bhoraskar

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      A modified electron bombardment type ion source suitable for use with mass spectrometer is described. Ion formation occurs throughout a relatively large volume in the ionisation box, since no magnetic field is used to collimate the ionising electrons. A sensitivity of 2 × 10−5 amp/torr is obtained for an ion extraction energy of 2 keV and 200 mass resolution. Trajectory tracing has been used to study the operation of the ion source. Capability of the ion source to analyse solid samples in microgram quantity was tested by studying evaporation of BaO from tungsten.

    • Thermally stimulated current spectra in nitrogen implanted fluorinated ethylene propylene

      J P Jog S B Ogale S J Walzade A S Ogale S V Bhoraskar M R Bhiday V N Bhoraskar

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      Thermally stimulated current spectra of nitrogen implanted fluorinated ethylene propylene polymer foils have been studied. Two characteristic peaks have been obtained for samples implanted with nitrogen ions with energies ranging from 20 to 60 keV. The variations in the activation energies and relaxation times of charge carriers, as a function of implantation energy, have been attributed to the corresponding changes in the carrier distribution in the polymer. The carrier mobilities and mobility life-time products have also been estimated for the two characteristic peaks.

    • Resistance changes in thin metallic films under ion bombardment

      S B Ogale S V Ghaisas A S Ogale V N Bhoraskar M R Bhiday

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      Resistance changes in thin films of copper, aluminium and bismuth have been studied under the bombardment of nitrogen, carbon and argon ions. Variations in resistance with implantation dose have been observed upto doses of ∼ 3 × 1017 ions/cm2 for ion energies in the range 40 to 120 keV. The results are discussed in terms of desorption of gases from the film and a composite action of sputter removal of the film and its structural changes upon ion bombardment. A simple theoretical model is discussed which can qualitatively explain the experimental observations.

    • Single-cavity 8 MeV race-track microtron

      V B Asgekar R K Bhalla B S Raye M R Bhiday V N Bhoraskar

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      This paper describes the operational details of the single-cavity race track microtron of this laboratory. The machine is capable of providing electrons of 8 MeV energy at 1 mA peak current. Important parameters of the machine and beam handling system are studied and the results are reported.

    • Gas pressure regulation in a r.f. ion source

      S S Jayantha Kumar V K Chindhade V N Bhoraskar

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      An experimental technique by which devterium gas pressure in a radio frequency ion source is automatically controlled and maintained to its initial set value is described. The accuracy achieved is ± 0.5 µ in about 5 µ gas pressure being used in the r.f. ion source of the neutron generator of this laboratory.

    • Modified vacuum vibrator ion source for phosphorous and boron ions

      N K Patil P N Kulkarni M R Bhiday V N Bhoraskar

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      A modified version of vacuum vibrator ion source is designed, fabricated and used to obtain phosphorous and boron ions. Its main features (i) controlled amplitude of vibrations at the spark position and (ii) small quantity requirements of materials. Pure powders of boron and red phosphorous were used respectively to get boron and phosphorous ions and in each case the ion current obtained was of the order of 1µA. The results obtained from silver electrodes are compared with those obtained from other metal electrodes. Silver is found to be a suitable electrode material for production of phosphorous and boron ions.

    • Cross-sections of a few (n,α) and (n, p) reactions induced at 14.7 MeV neutrons

      G R Pansare P M Dighe V N Bhoraskar

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      Cross-sections of the nuclear reactions27Al(n, p)27Mg,30Si(n, α)27Mg,52Cr(n, p)52V,53Cr(n, p)53V,54Cr(n, p)54V,54Cr(n, α)51Ti and120Sn(n, α)117Cd at 14.7 Mev neutrons were measured using56Fe(n, p)56Mn and27Al(n, α)24Na as monitor reactions. For comparison, theoretical values of the cross-section for these reactions were also obtained through different approaches of compound nucleus theory and computer code Alice. Accuracies achieved in the present measured values of the cross-sections are better than those available in literature.

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