• J N Das

      Articles written in Pramana – Journal of Physics

    • Triboluminescence, a new tool to investigate fracture-initiation time of crystals under stress

      B P Chandra N Periasamy J N Das

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      The present paper reports that triboluminescence (TBL) does not appear at the instant of impact of the load but a certain time lag is required for its appearance which depends on the value of the stress applied to the crystal. Since TBL appears in sugar crystals during the creation of new surfaces, the fracture-initiation time of the crystal has been taken to be the delay time in observing TBL pulse after the application of stress. The dependence of fracture-initiation time,tfσ, of crystals on the stress, σ, may be expressed astfσ=to exp (− ασ), whereto and α are constants. The values of the lattice energy, and the change in lattice energy per unit stress, of sugar crystals have been calculated from TBL measurements and they have been found to be 21·2 kcal mole−1 and 0·41 × 10−8 kcal mole−1 dyne−1 cm2 respectively.

    • 2S-excitation of atomic hydrogen by electrons at intermediate energies

      J N Das N Saha

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      The method of Das developed recently to analyse elastic scattering of electrons by atoms has been extended in the present paper to inelastic scatterings. The method has been applied for the computation of 2S-excitation, cross-sections at two typical intermediate energiesviz. 54.4 eV and 100 eV energies. Some of the results are compared with available experimental results and are found to be in satisfactory agreement with these.

    • Symmetric scattering ine±-H ionization collisions

      J N Das Samita Seal

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      Triple differential cross-sections for ionization of hydrogen atoms by electrons and positrons have been calculated for symmetric coplanar geometry following a multiple scattering method suggested and used earlier by the authors. Results show single binary peaks exactly at 45° and double binary peaks exactly at 135° for higher energies as are expected from an analysis of Briggs [3]. At lower energies there are certain deviations from these values. An analysis of scattering mechanism at peaks are also given. This supports Briggs’ explanation.

    • Triple differential cross sections for ionization of hydrogen atoms by positrons in a Schwinger variational calculation

      J N Das A Dey K Chakrabarti

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      Schwinger variational principle has been used to calculate triple differential cross-sections for ionization of hydrogen atoms by positrons at intermediate and high energies for Ehrhardt type asymmetric geometry. The results agree in general with the calculations of Brauneret al [8] and with the second Born calculation.

    • Weak correlation theory of electron hydrogen atom ionization collisions

      J N Das K Chakrabarti

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      A hyperspherical partial wave method of Das to calculate cross sections for ionization of hydrogen atoms by electrons has been applied for low energies. Here effect of coupling among different partial waves is neglected.

    • Symmetric scattering in electron and positron impact ionization of metastable 2s-state hydrogen atoms

      J N Das S Dhar

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      Triple differential cross sections for ionization of hydrogen atoms in the metastable 2s-state by the impact of electrons and positrons have been calculated for coplanar symmetric geometry. In this calculation a multiple scattering theory due to Das [10] and Das and Seal [11] has been used. An analysis of the results reveals that unlike scattering from the ground state, scattering from 2s-state is essentially a higher order process except for the binary collision direction. Moreover, here, the cross section results for 2s-state are much larger compared to those for scattering from the ground state. It is also found that the ionization mechanism at large scattering angles for ionization from the 2s-state is different from that for ionization from the ground state.

    • Hyperspherical calculation for electron hydrogen atom ionization collisions in a symmetric form

      J N Das

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      The hyperspherical partial wave method (Das [7]) has been presented here in a symmetric form so that effects of coupling among different partial waves may be included in a systematic way. It is also outlined here how to solve the relevant coupled set of radial wave equations numerically. Some preliminary results are presented forS, P andD waves in the low energy domain of 30–50 eV for the incident electron. In this calculation only two important partial waves are included in each channel. The results are compared with experimental ones and appear very encouraging.

    • Energy spectrum of ejected electrons in ionization of hydrogen atoms by electrons

      J N Das S Dhar

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      Energy spectrum of ejected electrons in ionization of hydrogen atoms has been calculated following a multiple scattering theory of Das and Seal [15]. The results show peaks around two to three Rydbergs of energies of the ejected electrons, for incident electron energy of 250 eV and 500 eV, considered here, and for different combinations of the angular variables of the scattered and the ejected electrons, for scattering in a plane. The peaks are very similar to those observed in relativistic K-shell ionization of Ag atoms by electrons at 500 KeV energy [6]. The physical origin of these peaks may be traced to the second order scatterings, scattering first by the atomic nucleus (or the atomic electron) and then a second time by the atomic electron. These peaks are, however, absent in the first Born results. Experimental verification of the present results and theoretical calculation by some other well-known methods will be interesting.

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