Time filter

Source Type

Samanta R.,Ramakrishna Mission Residential College | Purkait M.,Ramakrishna Mission Residential College | Mandal C.R.,Jadavpur University
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

Cross sections for single-electron capture in collisions of He2 +, Liq+ (q = 1,2,3), C6+, and O8+ ions with helium atoms at incident energy ranging from 50 to 5000 keV/amu have been calculated in the framework of four-body boundary-corrected continuum intermediate state (BCCIS-4B) approximation in both prior and post forms. In this formalism, distortion in the final channel related to the Coulomb continuum states of the projectile ion and the active electron in the field of residual target ion are included. In all cases, total single-electron-capture cross sections have been calculated by summing over all contributions up to n = 3 shells and subshells, respectively. It has been observed that the contribution of the capture cross section into the excited states is significant for asymmetric collision (ZP>lZT) and is insignificant for symmetric collision. Numerical results for the total cross sections show good agreement with the available experimental findings, particularly in the post form. Post-prior discrepancy has been found to be within 30% except for Li + + He interactions below 150 keV/amu. © 2011 American Physical Society.


Jana S.,Ramakrishna Mission Residential College | Mal C.R.,Jadavpur University | Purkait M.,Ramakrishna Mission Residential College
Journal of Physics B: Atomic, Molecular and Optical Physics | Year: 2015

Single-electron capture by a bare ion from a helium atom at intermediate and high energies in the framework of four-body distorted wave (DW-4B) approximation in both prior and post form has been considered. In the entrance channel, the initial bound state wave function is distorted by the incoming projectile ion, and the corresponding distortion is related to the Coulomb continuum states of the active electron and the residual target ion in the field of the projectile ion respectively. Continuum states of the active electron and the projectile ion in the field of the residual target ion are also included in the exit channel. It may be mentioned that the effect of dynamic electron correlation is explicitly taken into account through the complete perturbation potential. The total single-electron capture cross sections are obtained by summing over all contributions up to n = 3 shells and sub-shells respectively. In addition, the differential cross section for alpha particle-helium collision are calculated at impact energies of150, 300, 450, and 630 keV amu, respectively. Thecross section exhibit a monotonically decreasing angular dependence, withclear peak structures around 0.1 to .2 mrad being found at low impact energies. The current theoretical results, both in prior and post forms of the transition amplitude for symmetric and asymmetric collision, are compared with the available theoretical and experimental results. Current computed results have been found to be satisfactory in comparison with other theoretical and experimental findings. © 2015 IOP Publishing Ltd.


Purkait M.,Ramakrishna Mission Residential College
Journal of Physics: Conference Series | Year: 2015

Double-differential cross sections (DDCS) for electron emission in ionization under the impact of dressed projectiles has been calculated within the framework of three-Coulomb wave (3CW) model. The interaction between the dressed projectile ion and the active electron is approximated by a model potential. In order to take into account of the effect of the passive electrons, we have also constructed a model potential which satisfies initial condition and the corresponding wave function has been calculated from the model hamiltonian of the active electron in the target. © Published under licence by IOP Publishing Ltd.


Mondal A.,Ramakrishna Mission Residential College | Purkait M.,Ramakrishna Mission Residential College
Journal of Physics: Conference Series | Year: 2015

We investigate angular differential cross sections for double-electron and single-electron capture in ion- atom collisions for the intermediate and high energy region. We see the diffraction pattern in the spectrum of differential cross sections in the high energy range, i.e. another peak at 0.75 mrad in addition to Thomas peak at 0.47 mrad have been observed. © Published under licence by IOP Publishing Ltd.


Samanta R.,Ramakrishna Mission Residential College | Purkait M.,Ramakrishna Mission Residential College
Physica Scripta | Year: 2011

Single-electron capture in p-He collisions has been calculated at incident projectile energies ranging from 20 to 11 000 keV by means of the four-body boundary corrected continuum intermediate state approximation. The effect of dynamic electron correlations is explicitly taken into account through the complete perturbation potentials. Total single-electron capture cross-sections have been calculated by summing over the contributions up to n=2 shells and sub-shells. The differential cross-sections are calculated at impact energies in the range from 30 to 300 keV. Overall, the calculated cross-sections are in good agreement with recent experimental findings. © 2011 The Royal Swedish Academy of Sciences.


Mondal S.,Korea Astronomy and Space Science Institute | Mondal S.,Ramakrishna Mission Residential College | Choi C.S.,Korea Astronomy and Space Science Institute
New Astronomy | Year: 2013

In the present study, we notice that within a few gravitational radii, where the X-ray emission originates, the perturbations in the accretion disk may excite high frequency quasi-periodic oscillations (QPOs). The vertical and the radial disk oscillations frequencies due to the perturbation exhibit a 3:2 twin-peak ratio which is most commonly detected in the X-ray fluxes in many Galactic micro-quasars. The high frequency QPOs happen most likely if the oscillations occur very close to the center. We further notice that the perturbations originate in the neighborhood of the shock transition or from a discontinuity in the disk, and could be the possible mechanism to excite the high frequency QPOs. The shocks are more probable in the X-ray emission region and may form very close to the horizon particularly, when the black hole spin is very high. Studying the shock locations as a function of the black hole spin in a fully general relativistic inviscid transonic accretion flows, we calculate the disk oscillation frequencies and their ratios in that perturbed orbit. Further, from the spin dependence, we estimate the 'most probable spin interval' in the micro-quasars by considering the 1/M scaling hypothesis in high frequency QPOs. Finally, we find the spin (a) interval which lies for XTE 1550-564, at a ∼ (0.89-0.99), for the GRO 1655-40, at a ∼ (0.96-0.99) and for the GRS 1915+105, at a ∼ (0.74-0.999). The uncertainty in the mass analysis corresponds to the above spin intervals. © 2012 Elsevier B.V. All rights reserved.


Samanta R.,Ramakrishna Mission Residential College | Purkait M.,Ramakrishna Mission Residential College
European Physical Journal D | Year: 2011

Four-body formalism of boundary corrected continuum intermediate state (BCCIS-4B) approximation have been applied to calculate the single-electron capture cross sections by fast protons through some helium-like ions in a large energy range from 30-1000 keV. In this model, distortion has been taken into account in the entrance channel. In the final channel, the passive electron plays the role of screening of the target ion. However, continuum states of the projectile and the electron in the field of the residual target ion are included. The comparison of the results is made with those of other theoretical investigations and experimental findings. The present calculated results are found to be in good agreement with the available experimental findings. © 2011 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.


Mondal S.,Korea Astronomy and Space Science Institute | Mondal S.,Ramakrishna Mission Residential College
Astrophysical Journal | Year: 2010

In the Galactic microquasars with double peak kHz quasi-periodic oscillations (QPOs) detected in X-ray fluxes, the ratio of the twin-peak frequencies is exactly, or almost exactly 2:3. This rather strongly supports the fact that they originate a few gravitational radii away from its center due to two modes of accretion disk oscillations. Numerical investigations suggest that post-shock matter, before they settle down in a subsonic branch, execute oscillations in the neighborhood region of "shock transition". This shock may excite QPO mechanism. The radial and vertical epicyclic modes of oscillating matter exactly match with these twin-peak QPOs. In fully general relativistic transonic flows, we investigate that shocks may form very close to the horizon around highly spinning Kerr black holes and appear as extremum in the inviscid flows. The extreme shock location provides upper limit of QPOs and hence fixes "lower cutoff" of the spin. We conclude that the 2:3 ratio exactly occurs for spin parameters a ≥ 0.87 and almost exactly, for wide range of spin parameter, for example, XTE 1550-564, and GRO 1655-40 a>0.87, GRS 1915+105 a>0.83, XTE J1650-500 a>0.78, and H 1743-322 a>0.68. We also make an effort to measure unknown mass for XTE J1650-500(9.1 ∼ 14.1 M ⊙) and H 1743-322(6.6 11.3 M ⊙). © 2010. The American Astronomical Society.


Jana S.,Ramakrishna Mission Residential College | Purkait M.,Ramakrishna Mission Residential College
Indian Journal of Physics | Year: 2014

Total as well as projectile angular-differential cross sections for transfer and transfer-excitation have been investigated in collision of α-particles with helium atoms in the energy range 50-5,000 keV/amu. The four-body Coulomb-Born distorted wave formalism and boundary corrected continuum intermediate state approximation have been applied for this rearrangement collision. In both methods dynamic electron correlations have been taken through the complete perturbation potentials in post form. It is shown that for single electron-transfer, the ground state capture is dominant and the contribution from excited states to the total cross section is less important. It is also noted that the cross sections for transfer with target excitation channel have minor contribution to the total cross sections. We have also studied the total cross sections for single electron transfer from lithium atom by α-particle impact in the energy range from 50 to 3,000 keV/amu. Present computed results, both in prior and post forms of the transition amplitude for symmetric and asymmetric collisions, agree reasonably with the available theoretical and experimental results. © 2013 Indian Association for the Cultivation of Science.


Jana S.,Ramakrishna Mission Residential College | Samanta R.,Ramakrishna Mission Residential College | Purkait M.,Ramakrishna Mission Residential College
European Physical Journal D | Year: 2012

Three-Coulomb wave model (3C) is used to investigate the angular distributions of electron ejected from ground state atomic hydrogen by the impact of 1 MeV/amu and 2.5 MeV/amu C 6+ions and 95 keV H + ions. The final state wavefunction incorporates distortion due to three-body mutual Coulombic interaction. The forward-backward angular asymmetry in the low energy electron emission has been studied. The present computed results have been compared with the available experimental results and with the theoretical calculations using alternative methods. We found that our computed results are in good agreement with the experimental observations compared to other theoretical findings. DDCS peak is reproduced by the present calculation and is verified by CDW-EIS theory for C 6++ H collision. In addition, DDCS results for ionization are given in tabular form. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2012.

Loading Ramakrishna Mission Residential College collaborators
Loading Ramakrishna Mission Residential College collaborators