共查询到20条相似文献,搜索用时 15 毫秒
1.
The differential and total cross sections for the pair production of doubly heavy diquarks are calculated analytically within the diquark model. The cases of electron-positron and quark-antiquark annihilation are considered. The ratios of the total cross sections to the corresponding cross sections for annihilation into two heavy quarks are estimated numerically. 相似文献
2.
M. I. Chibisov F. Brouillard M. Cherkani 《Journal of Experimental and Theoretical Physics》2001,92(3):400-411
The cross sections of the detachment of one and two electrons during the collision of two negative ions H? + H?, H? + Cs?, and Cs? + Cs? are calculated in a wide range of collision energies: from the energy threshold to approximately 100 keV. In adiabatically slow collisions, the detachment of electrons occurs as a result of one-or two-electron Auger decays whose rates are calculated in the approximation of asymptotically large separations between ions. For high collision energies, the cross sections of the electron detachment are calculated by the method of close coupling of states. The calculated cross sections are in good agreement with the results of experimental measurements made for the H? + H? collision. 相似文献
3.
《Physics letters. A》2019,383(21):2488-2491
We calculated the cross sections of ultra-soft x-ray bremsstrahlung in electron scattering upon Ar, Kr and Xe. The results are consistent with the absolute values of the differential cross sections measured by Gnatchenko et al. (2009) [17] for scattering electrons with an energy of 600 eV on these atoms. 相似文献
4.
Interference effects on the photoionization cross sections between two neighbouring atoms: nitrogen as an example
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Interference effects on the photoionization cross sections
between two neighbouring atoms are considered based on the coherent
scattering of the ionized electrons by the two nuclei when their
separation is less than or comparable to the de Broglie wave length
of the ionized electrons. As an example, the single atomic nitrogen
ionization cross section and the total cross sections of two
nitrogen atoms with coherently added photoionization amplitudes are
calculated from the threshold to about 60~\AA (1~\AA=0.1~nm) of the
photon energy. The photoionization cross sections of atomic nitrogen
are obtained by using the close-coupling R-matrix method. In the
calculation 19 states are included. The ionization energy of the
atomic nitrogen and the photoionization cross sections agree well
with the experimental results. Based on the R-matrix results of
atomic nitrogen, the interference effects between two neighbouring
nitrogen atoms are obtained. It is shown that the interference
effects are considerable when electrons are ionized just above the
threshold, even for the separations between the two atoms are larger
than two times of the bond length of N2 molecules. Therefore, in
hot and dense samples, effects caused by the coherent interference
between the neighbours are expected to be observable for the total
photoionization cross sections. 相似文献
5.
Dr. K. Löns 《Zeitschrift für Physik A Hadrons and Nuclei》1968,215(1):1-16
Differential cross sections for direct pair production by electrons with total energiesE 0=5.511 and 32 MeV in copper are calculated in lowest order of pertubation theory and Born approximation, including the matrix elements of the electron exchange effect. Integration over particle angles and — in the case ofE 0=32 MeV — over the energy of one outgoing electron was performed numerically on an IBM 7044 computer by using Gaussian quadrature formulas in FORTRAN-programs. The results forE 0=5.511 MeV show a severe reduction of the differential cross section due to the exchange effect, while the results for 32 MeV are in fairly good agreement with the pair production experiment performed byCriegee in 1959. 相似文献
6.
The process of polarized electron-positron pair photoproduction via a polarized γ quantum in a crystalline medium is investigated
using a new method that considers the distribution of nucleus charges and atomic electrons. Real changes in the cross sections
of both polarized and nonpolarized electron pair production, and in the degrees of particle polarization in silicon crystal,
are obtained. 相似文献
7.
R. Müller-Fiedler P. Schlemmer K. Jung H. Ehrhardt 《Zeitschrift für Physik A Hadrons and Nuclei》1985,320(1):89-94
Triple differential cross sections have been measured for electron impact ionization of helium at 256 eV collision energy, 3 eV energy of the slow outgoing electrons and scattering angles of the fast outgoing electrons of 4°, 6°, 8°, and 10°. The data have been put on absolute scale by extrapolating the generalized oscillator strength to zero momentum transfer. In this optical limit the triple differential cross sections can be normalized by using the well-known cross sections for photoionization. The experimental data are compared with results of different theoretical approaches. For nearly all calculated curves rather good agreement with the measurements is obtained for the relative shape of the binary peak, while often its absolute cross section is overestimated. Concerning the recoil peak, larger discrepancies are found with respect to both, relative shapes and cross sections. A perceptible improvement can be stated for calculations which have been performed in a distorted wave approximation and in second Born approximation. 相似文献
8.
9.
The spectral distribution of the absolute differential cross section for total bremsstrahlung, including ordinary and polarization, for the scattering of 0.6-keV electrons from free xenon atoms has been measured. The bremsstrahlung photons have been detected at an angle of 97° with respect to the electron motion direction. The investigations have been carried out in the ultrasoft x-ray spectral region 60–240 eV. The results are compared with the total cross sections for bremsstrahlung calculated in several approximations for the scattering of 5-and 25-keV electrons by Xe atoms. Both the value and the spectral distribution of the experimental absolute cross sections are most satisfactorily reproduced by the calculations in the distorted partial wave approximation. 相似文献
10.
11.
Electron impact ionization cross sections of Ne, Ar, Kr, and Xe atoms are numerically calculated. The electron perturbation
in the continuous spectrum in the target field is taken into account. The matrix elements are calculated in many-electron,
nonrelativistic approximation with allowance for the superposition of configurations and relaxation effect. The radial part
of the electron wave function in the continuum is calculated by solving the single-configuration Hartree-Fock equation. The
wave functions of electrons in the continuum are orthogonalized with respect to the core orbital functions. The calculated
cross sections are compared to the experimental data and calculations made using the plane-wave Born approximation and that
involving generalized oscillator strengths. 相似文献
12.
13.
In this current work an cross section data for HCI elementary processes were calculated on the base of calculated and experimental data comparison on electrons drift rate and Townsend coefficients of dissociative attachment. Cross sections data of HCI electronic excitation are obtained for the first time. 相似文献
14.
Yu. M. Smirnov 《Optics and Spectroscopy》2003,94(3):327-331
Excitation of spectral lines of SrII, including laser lines, is studied experimentally in collisions of slow electrons with strontium atoms. Twenty-one excitation cross sections are measured at an energy of electrons of 30 eV. Five optical excitation functions are recorded at an energy ranging from 0 to 200 eV. Direct-excitation cross sections for the 5p 2 P°1/2, 3/2 levels and the contribution to their population by cascade transitions are calculated. Excitation cross sections of two laser transitions in the IR spectral region are determined using known branching ratios. The results obtained are compared with data of previous experiments. 相似文献
15.
The cross sections for excitation of surface plasmons by fast electrons and x rays are calculated within the random phase approximation for a spherical metal particle. The results are compared with those obtained within the hydrodynamic model of a free electron gas. 相似文献
16.
Takeshi Mukoyama 《X射线光谱测定》2018,47(4):320-326
The N‐subshell ionizations cross sections of heavy elements by proton impact have been calculated in the binary‐encounter approximation. The momentum distribution of target electrons is taken into account by the use of the nonrelativistic and relativistic hydrogenic models and the Hartree–Fock–Roothaan and the relativistic Hartree–Fock–Roothaan methods. The obtained subshell ionization cross sections are compared with the experimental data and other theoretical calculations. The electronic relativistic effect and the wave‐function effect on N‐shell ionization cross sections are discussed. 相似文献
17.
Joachim Kessler 《Zeitschrift für Physik A Hadrons and Nuclei》1964,182(2):153-165
Cross sections for small angle scattering of electrons are determined from the absolute measurements of the foregoing paper.Lenz's approximation of the cross sections proves to be valid but in a very limited angular range for most elements. Deviations from results calculated withLenz's theory can be ascribed to this reason in all in vestigated cases. Determination of the cross sections shows that the Thomas-Fermi-Dirac-model describes small angle scattering much better than is commonly assumed, disregarding a very small range near the angle 0 into which but a very small portion of the electrons is scattered.Lenz's method, however, yields only in special cases the correct cross sections and must not be as commonly used as is general practice. 相似文献
18.
19.
Ebrahim Ghanbari-Adivi Azime Najafabadi Velayati 《Central European Journal of Physics》2014,12(3):192-202
The four-body Coulomb-Born distorted-wave approximation with correct boundary conditions (CBDW-4B) is applied to the K-shell positronium formation from multi-electron atoms at intermediate and high impact energies. In the present approach, both K-shell electrons are treated as active electrons. For collisions of positrons with helium, carbon, and neon atoms, both the post and prior forms of the transition amplitude are calculated and the corresponding differential and integral cross sections are compared with the results of the three-body version of the formalism (CBDW-3B). In order to investigate the effects of the static electronic correlations on the process, initial bound states of the active electrons in helium atoms are described by Hylleraas and Silverman wave functions. Also for positronium formation from helium atoms the obtained cross sections are compared with the available experimental data and also with the results of the other theories. 相似文献
20.
Andrzej Adamczak 《Hyperfine Interactions》1993,82(1-4):91-98
The results of first calculations of the differential cross sections for muonic hydrogen scattering on hydrogen molecules are presented. They are functions of the initial and final kinetic energy of the system and the scattering angle. These calculations are based on the respective set of cross sections for muonic hydrogen scattering on hydrogen nuclei, obtained within the framework of the adiabatic method. The Fermi pseudopotential method is used to estimate the molecular binding effects. The influence of electrons on the cross sections under consideration is described in terms of the effective screening potential. Rotational and vibrational transitions are taken into account. The calculated molecular differential cross sections show a strong angular dependence. This effect is very significant for the electronic contributions to the cross sections, e.g. for collision energies above approximately 0.1 eV only the cross sections of small scattering angles are influenced considerably by the screening. Since these differential cross sections give detailed information about the final energies and complicated angular distributions of the scattered muonic atoms they are the proper basis for calculations concerning the deceleration of muonic hydrogen atoms in molecular hydrogen targets and for Monte Carlo simulations of different experiments in muonic physics. 相似文献