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Articles 1 - 4 of 4
Full-Text Articles in Physics
Timing Of Pair Production In Time-Dependent Force Fields, Christopher C. Gerry, Q Su, Rainer Grobe
Timing Of Pair Production In Time-Dependent Force Fields, Christopher C. Gerry, Q Su, Rainer Grobe
Faculty publications – Physics
We examine the creation and annihilation dynamics for electron-positron pairs in a time-dependent but subcritical electric force using a simplified model system. Numerical and semianalytical solutions to computational quantum field theory show that despite the continuity of the quantum field operator in time, the actual number of created particles can change in a discontinuous way if the field changes abruptly. The number of permanently created particles after the pulse, however, increases continuously with the duration of the electric field pulse, suggesting a transition from an exclusive annihilation to a creation regime.
Electron-Impact Ionization Of L-Shell Atomic Species, Abul Kalam Fazlul Haque, M A. Uddin, A K. Basak, Khondkar R. Karim, B C. Saha, F B. Malik
Electron-Impact Ionization Of L-Shell Atomic Species, Abul Kalam Fazlul Haque, M A. Uddin, A K. Basak, Khondkar R. Karim, B C. Saha, F B. Malik
Faculty publications – Physics
Electron impact ionization cross sections (EIICS) of 30 L-shell targets, with open- and closed-shell configurations in the isoelectronic sequences ranging from Li to Ne, are evaluated using the generalized parameters of our recent modification of BELL formula (MBELL) [Haque , Phys. Rev. A 73, 012708 (2006)]. Three sets of parameters, one each for the 1s, 2s, and 2p orbits, provide an excellent account of the experimental EIICS data of atomic targets, neutral and ionic, up to the atomic number Z=92 and incident energies up to about 250 MeV. In comparison with the quantum mechanical predictions, it is found that the …
Interpretational Difficulties In Quantum Field Theory, P Krekora, Q Su, Rainer Grobe
Interpretational Difficulties In Quantum Field Theory, P Krekora, Q Su, Rainer Grobe
Faculty publications – Physics
Based on space-time-resolved solutions to relativistic quantum field theory we illustrate interpretational difficulties in associating field-theoretical quantities with properties of particles. These difficulties are related to the fact that the definition of the spatial probability density of particles depends on the choice of the Hilbert subspace on which the field operator is projected. We illustrate these problems by analyzing pair-production probabilities and spatial densities for the electron-positron dynamics associated with a spatially localized subcritical potential that is turned on and off in time.
Empirical Model For The Electron-Impact K-Shell-Ionization Cross Sections, A K. F Haque, M A. Uddin, A K. Basak, K R. Karim, B C. Saha
Empirical Model For The Electron-Impact K-Shell-Ionization Cross Sections, A K. F Haque, M A. Uddin, A K. Basak, K R. Karim, B C. Saha
Faculty publications – Physics
The total cross sections of electron-impact single-K-shell ionization of 14 atomic targets ranging from H to U (1 <= Z <= 92) are calculated using a modified version of the BELI formula [Bell , J. Phys. Chem. Ref. Data 12, 891 (1983)] by incorporating both ionic and relativistic corrections in it. The proposed modified Bell model with a single set of parameters is found to provide an excellent description of the experimental data in the reduced energy range 1 <= E/I-K <= 10(6) (E and I-K are, respectively, the incident energy and ionization potential) with a performance level at least as good as any of the existing methods and models.