Articles written in Pramana – Journal of Physics

    • A. C. behaviour and dielectric relaxation in indium oxide films

      A Goswami Amit P Goswami

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      Vacuum deposited blackish indium oxide films (In-O) as well as the oxidised films (In2O3) were studied for their a.c. behaviour at different temperatures and at various film thicknesses in the audio frequency region. ε of In-O films was thickness dependent and also showed dielectric relaxation at lower frequencies due to the dipolar orientation arising from their non-stoichiometric nature. However at liquid nitrogen temperature region ε was thickness independent similar to the oxidised films which neither showed any relaxation effect nor any thickness dependent ε. The results have been discussed from the classical theory of dielectric polarisation.

    • Correlation between fractional independent yields and neutron-to-proton ratio of fission products in low energy fission

      A Goswami B K Srivastava Alok Srivastava S B Manohar Satya Prakash M V Ramaniah

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      Fractional independent yields of fission products in the thermal neutron-induced fission of233U,235U,239Pu,241Pu and in the spontaneous fission of252Cf have been correlated with the neutron-to-proton ratio of the fission products. The yields of the products from a fissioning system, when plotted as a function of neutron-to-proton (N/Z) ratio of fission preducts, fall on two Gaussian distribution corresponding to light and heavy fission products. The centroids of the distribution or the most probable value of neutron-to-proton ratio is found to be very close to theN/Z of the fissioning nucleus. From the most probable value ofN/Z the various parameters of charge distribution e.g. most probable massAp, most probable chargeZp, the mass dispersionσAand the charge dispersionσZhave been obtained and are in good agreement with the experimental values ofApandZp.

    • Incomplete fusion reactions in 16O+165Ho

      Anil Sharma B Bindu Kumar S Mukherjee S Chakrabarty B S Tomar A Goswami G K Gubbi S B Manohar A K Sinha S K Datta

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      Excitation functions for evaporation residues of the system 16O + 165Ho have been measured up to 100 MeV. Recoil range distribution of long lived reaction products were measured at 16O beam energy of 100 MeV. Detailed Monte Carlo simulation of recoil range distributions of products were performed with the help of PACE2 code, in order to extract the contributions of incomplete fusion in the individual channels. The results clearly show the incomplete fusion contributions in the tantalum and thulium products. This is confirmed by the predictions of breakup fusion model of the incomplete fusion.

    • Design of a spiral inflector and transverse beam matching for K130 cyclotron at the Variable Energy Cyclotron Centre


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      This paper describes the design of a spiral inflector for inflecting heavy ion beams into the existing central region of the K = 130 Variable Energy Cyclotron at Kolkata. Simulation results of transverse beam dynamics through the spiral inflector and the effect of the fringe field on beam phase ellipses at its exit have been discussed in the absence of space charge effect. We have also made an effort to minimise the effect of inflector fringe field by properly adjusting the inflector voltage. The proper matching conditions in the central region have been obtained by optimising the system parameters of the existing axial injection line of K130 cyclotron. The tracking of particles that belong to the boundary of the optimised phase ellipses at the matching point has also been carried out in the computed electric and magnetic fields in the central region. Simulation results confirm that the optimised beam condition reduces beam losses for further acceleration in the cyclotron.

    • Effect of solenoid misalignment on the injection efficiency for K500 superconducting cyclotron at VECC


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      This paper describes the beam transmission characteristics through the spiral inflector and in the central region of the K500 superconducting cyclotron at VECC due to solenoid magnet misalignment in its vertical injection line. The equations of motion for a particle in misaligned solenoidal channel are derived from the Hamiltonian and used to investigate the behaviour of the beam during injection where the axial magnetic field of the cyclotron plays an important role. We have optimised the solenoid strength in the vertical line to reduce transmission loss in the spiral inflector and to match the beam in the central region of the cyclotron. The percentage of the accepted particle in the spiral inflector and in the central region are calculated for different values of translational and rotational misaligned parameters of the solenoids. The allowed tolerances of these parameters are obtained to get the desired injection efficiency.

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