• R K SINGH

      Articles written in Pramana – Journal of Physics

    • Ionization states of cosmic rays:Anuradha (IONS) experiment in Spacelab-3

      S Biswas R Chakraborti R Cowsik N Durgaprasad P J Kajarekar R K Singh M N Vahia J S Yadav N Dutt J N Goswami D Lal H S Mazumdar D V Subhedar M K Padmanabhan

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      The measurements of the ionization states, composition, energy spectra and spatial distribution of heavy ions of helium to iron of energies 10–100 MeV/amu in the anomalous cosmic rays are of major importance in understanding their origin which is unknown at present.Anuradha (IONS) cosmic ray experiment in Spacelab-3 was designed to determine the above properties in near earth space and this had a highly successful flight and operations aboard the shuttle Challenger at an orbital altitude of 352 km during 29 April to 6 May 1985. The instrument employs solid state nuclear track detectors (CR-39) of high sensitivity and large collecting area of about 800 cm2 and determines the arrival time information of particles with active elements. Experimental methods, flight operations and preliminary results are briefly described. Initial results indicate that relatively high fluxes of low energy cosmic ray α-particles, oxygen group and heavier ions were obtained. The flight period corresponded to that of quiet Sun and the level of solar activity was close to solar minimum. It is estimated that about 10,000 events of low energy cosmic ray alpha particles with time annotation are recorded in the detector together with similar number of events of oxygen and heavier ions of low energy cosmic rays.

    • A three-body force shell model calculation of Schottky defect formation energies of ionic crystals with CsCl structure

      V Mishra S P Sanyal R K Singh

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      A three-body force shell model (TSM) for the calculation of Schottky defect formation energies in solids with cesium chloride structure has been developed by incorporating the effects of long-range three-body interactions (TBI) in the shell model. These TBI in the defect lattice arise from the deformation of electron shells when the nearest neighbour ions get relaxed from their equilibrium position. This model has been used to calculate the cation and anion extraction and Schottky defect formation energies of CsCl, CsBr, CsI, TlCl, TlBr and NH4Cl crystals. The calculated values of these defect properties agree reasonably well with their measured values.

    • Elastic behaviour of lead fluoride under pressure

      R K Singh C N Rao

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      The variation of the second-order elastic constants (SOECs) and the longitudinal and shear modulii with hydrostatic pressure for the lead fluoride (PbF2) has been investigated for the first time by means of a three-body force potential (TBP) model. The significance of three-body interactions (TBI) has been clearly demonstrated in reproducing the elastic constant variations and the pressure derivatives of SOECs of PbF2. The equation of state for this crystal has also been reported.

    • Dynamics of the multispecies colliding plasmas of different atomic masses

      ALAMGIR MONDAL BHUPESH KUMAR R K SINGH H C JOSHI

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      Laser-produced plasma plumes and the subsequent interaction zone of multispecies colliding plasmas have been investigated in vacuum (at 5 × 10$^{−7}$ mbar) by using Nd:YAG nanosecond laser as the energy source.The key features such as shape, size, expansion dynamics of the primary plumes and the resulting interaction zone have been examined by using a combination of solid targets (e.g. Al–Ni and Al–W) with different atomic masses. Fast imaging technique has been utilised to visualise the formation and expansion dynamics of the primary plasma plumes as well as the interaction zone. Optical emission spectroscopy (OES) is used to estimate the electron temperature and density of the plasma plumes. Optical time of flight has been used to get the velocity of ion and neutral particles in the plasma plume. Time-resolved images of plumes show significant differences depending on the target materials and energy of the two beams. We have observed that the primary plasma plumes withnon-uniform expansion velocity produces interaction zone which expands at an angle in vacuum. Optimisation of laser energy imbalance has been done based on fast imaging results for the targets of different elements. These experimental findings can have important roles in the generation of multispecies plasma plumes and to control their species contribution in different applications, e.g. thin film deposition.

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