共查询到20条相似文献,搜索用时 31 毫秒
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N. V. Novikov Ya. A. Teplova 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2008,2(3):360-363
The single electron loss cross sections for fast B, N, and Ne ions colliding with He atoms are calculated. In the calculation of the ionization amplitude, the He nucleus screening is taken into account by both the sum rule and the summation over a finite number of excited 1snl (n < 5, l < 2) states and states of the continuous spectrum. The calculated results agree satisfactorily with experimental data. 相似文献
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A. A. Narits E. S. Mironchuk V. S. Lebedev 《Journal of Experimental and Theoretical Physics》2013,117(4):607-622
Electron-transfer processes are studied in thermal collisions of Rydberg atoms with alkaline-earth Ca(4s 2), Sr(5s 2), and Ba(6s 2) atoms capable of forming negative ions with a weakly bound outermost p-electron. We consider the ion-pair formation and resonant quenching of highly excited atomic states caused by transitions between Rydberg covalent and ionic terms of a quasi-molecule produced in collisions of particles. The contributions of these reaction channels to the total depopulation cross section of Rydberg states of Rb(nl) and Ne(nl) atoms as functions of the principal quantum number n are compared for selectively excited nl-levels with l ? n and for states with large orbital quantum numbers l = n ? 1, n ? 2. It is shown that the contribution from resonant quenching dominates at small values of n, and the ion-pair formation process begins to dominate with increasing n. The values and positions of the maxima of cross sections for both processes strongly depend on the electron affinity of an alkaline-earth atom and on the orbital angular momentum l of a highly excited atom. It is shown that in the case of Rydberg atoms in states with large l ~ n ? 1, the rate constants of ion-pair formation and collisional quenching are considerably lower than those for nl-levels with l ? n. 相似文献
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A new approximation method for the n-fermion problem is developed and tested within the exactly solvable model of Lipkin, Meshkov and Glick. Results are compared with the exact solutions and RPA. Applying the method to the 4He nucleus, excitation energies, total binding energy and the ground-state energies of 3He and 5He are calculated. 相似文献
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V. M. Bystritsky V. A. Varlachev G. N. Dudkin A. S. Nurkin B. A. Nechaev V. N. Padalko F. M. Pen’kov Yu. Zh. Tuleushev M. Filipowicz A. V. Philippov 《Journal of Experimental and Theoretical Physics》2017,125(5):741-751
The nature of background processes accompanying astrophysical nuclear reactions induced by hydrogen, helium, and neon ions in deuterated targets with small cross sections has been studied in calculations and experiments. The experiments have been performed at a Hall pulsed plasma accelerator in the ion energy range of 26–32 keV. The yield of background neutrons and γ-quanta with energies below 4 MeV in the proton-induced D(p, γ)3He reaction is primarily due to the presence of a natural impurity of gaseous deuterium in gaseous hydrogen and the chain of D(D, 3He)n → (n, γ) or (n, n'γ) reactions. A small contribution comes from the chain of D(1H, 1H)D → D(D, 3He)n → (n, γ) or (n, n'γ) reactions. It has been shown that background neutrons and γ-quanta from the D(4He, γ)6Li reaction are entirely due to the chain of D(4He, 4He)D → D(D, 3He)n → (n, γ) or (n, n'γ) reactions. It has been shown that the yield of neutrons and γ-ray photons detected at the interaction of neon ions with deuterated targets is also entirely due to the chain of elastic- scattering reactions of neon ions on deuterons in the target and to subsequent inelastic processes of interaction of deuterons accelerated at elastic scattering with other deuterons of the target. The main contribution to the yields of background neutrons and γ-quanta comes from doubly charged neon ions. The main conclusion is that the explanation of the yield of neutrons and γ-quanta at the interaction of hydrogen, helium, and neon ions with deuterated targets does not require “exotic” theoretical models. 相似文献
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The 6Li + n seven-nucleon nuclear system is studied at low energies within a microscopic approach based on the multichannel algebraic version of the resonating group model. The partial and total cross sections for the 6Li(n, t)4He reaction are calculated. The contributions of the various partial cross sections to the energy dependence of the total cross section are considered. The results of the calculations are found to be in a good agreement with experimental data. 相似文献
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We have measured the electron energy of the thermal group of electrons in both longitudinal and transverse electron beam created helium glow discharges. The measurement technique employs the ratio of intensities of spectral lines in the 2s3S?np3P He I series. Values of kTe between 0.07 and 0.11 eV were obtained. These energies are typical of the beam-generated electric field free plasmas. The competitive loss of helium ions by recombination and by charge transfer in a He?Hg electron beam created plasma is calculated. The results are applied to the Hg+ laser pumping scheme using a electron beam created He?Hg plasma. 相似文献
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V. V. Evstifeev N. V. Kostina I. A. Egorov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(4):647-653
The angular and energy distributions of Cs+ and Xe+ ions scattered by monatomic crystalline films have been calculated via the molecular dynamics method in the scope of the multiparticle interaction mechanism. The calculated dependences of scattered heavy ions with a low initial energy E 0 = 40 eV on the atomic mass, crystal lattice type, interatomic distance, and binding energy of the film atoms are discussed and compared with the experiment. The presented data can be used to predict the physical properties of a surface covered with a monatomic layer of foreign atoms during experimental surface studies based on the backscattering of ions with low initial energies. 相似文献
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H. W. Wolff K. Radler B. Sonntag R. Haensel 《Zeitschrift für Physik A Hadrons and Nuclei》1972,257(4):353-368
The absorption spectrum of atomic sodium in the photon energy region from 30 to 150 eV has been investigated. A great number of sharp absorption lines which can be attributed to the excitation of a 2p- or a 2s-electron has been detected. Simultaneous excitation of one 2p- and one 3s-electron gives rise to considerably strong broad and asymmetric absorption structures above the highest series limit (1 P 1) for the excitations of a single 2p-electron. Some of the assignments have been confirmed by Hartree-Fock calculations. The relative spectral dependence of the absorption cross-section in this energy range has been determined for the first time. The spectrum of free Na atoms has been compared with theL II, III spectrum of solid sodium. 相似文献
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Z. Šroubek 《Surface science》1974,44(1):47-59
The process by which atoms are ionized as they are sputtered from a metal surface has been analyzed both theoretically and experimentally. In the theoretical part the expressions for ionization coefficient R+ of atoms having the ionization energy much larger than the metal work function have been derived using a molecular orbital method. The effect of the level crossing was estimated in an approximate way. In the experimental part the SIMS experiments on clean Ni and Al surfaces and on Ni surface covered with a submonolayer of adsorbed K, Na and Al are reported. It has been found and it is for the first time reported that the energy distribution of ions sputtered from a submonolayer of adatoms is independent of energy (200–2500 eV) and mass (Ar+ Xe+ of incident ions and depends only upon the adsorption energy of the adatom. The energy distribution of ions sputtered from bulk samples has been found dependent on the primary ion energy. The measurement of the absolute value of R+ has shown that there is a strong correlation between the number of the adatom valence d-electrons and the value of R+, the value of R+ being smaller for atoms with more d-electrons. These experimental data have been compared with the theoretical expressions and the important role of the mechanism which takes into account the bending of the adatom energy level has been assessed. 相似文献
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J. Stroth H. Backe M. Begemann-Blaich K. Bethge H. Bokemeyer M. Dahlinger W. Konen P. Kosmadakis S. Mojumder P. Senger K. Stiebing 《Zeitschrift für Physik A Hadrons and Nuclei》1997,357(4):441-455
δ-electron emission in elastic and dissipative collisions of U+Au at E/A = 8.65 MeV has been investigated. The velocity vectors of the reaction products were measured in coincidence with electrons of energies up to 3.2 MeV. The δ-electron yield measured for elastic collisions is in good agreement with coupled-channels calculations. The δ-electron spectra of dissipative reactions show a clear dependence on the violence of the collision, i.e. the total kinetic energy loss (TKEL). The shape of the spectra are analysed with an atomic model by a fitting procedure using phenomenological trajectories. The results indicate an increasing contact time of the united system with increasing total kinetic energy loss reaching 1.16(4) × 10?21 s at < TKEL > = 375 MeV. 相似文献
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We present momentum-space properties of multiply ionized neon atoms as a function of the degree of ionization of the atom. In particular, we have calculated the Compton profiles of all possible ionized states of neon atoms with electronic configurations 1sm2sn2pq, m=1-2, n=0-2, q=0-6. The radial single-electron radial wave functions, obtained from the Hartree-Fock atomic model, were converted into momentum space wave functions by applying appropriate Fourier transformation. The values of the Compton profiles from the present calculation can be used to interpret experimental cross sections of variously ionized neon atoms colliding with other atoms. Compton profiles of neutral neon atoms, available in the literature, are in excellent agreement with the present calculation. 相似文献
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K. Wittmaack 《Physics letters. A》1979,69(5):322-325
The intensity and the energy distribution of Si+n cluster ions emitted from clean silicon have been measured for different target orientations as a function of the primary ion energy (3–30 keV) and the projectile mass (noble gas ion bombardment). The results favour the idea that clusters are emitted as such rather than being produced by vacuum recombination of individually emitted atoms and ions. 相似文献
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B. M. Smirnov 《Journal of Experimental and Theoretical Physics》2001,92(6):951-959
The asymptotic resonant charge exchange theory is developed for slow collisions of atoms and ions with valent p-electrons. Because of a small rotation angle of the molecular axis in the course of the p-electron transition, the resonant charge exchange cross section is not sensitive to the rotational energy of colliding particles, and the cross sections are nearly equal for cases “a”, “b”, and “d” of the Hund coupling, and also for cases “c” and “e” of the Hund coupling. The cross sections of the resonant charge exchange process are evaluated under various conditions and for various elements of the periodical table with p-electron shells of atoms and ions. 相似文献
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In the present work, experimental and computer simulation studies of low-energy (E0 = 80-500 eV) Cs+ ions scattering on Ta, W, Re target surfaces and K+ ions scattering on Ti, V, Cr target surfaces have been performed for more accurate definition of mechanism of scattering, with a purpose of evaluation of an opportunity of use of slow ions scattering as a tool of surface layers analysis. The choice of the targets was based on the fact that the ratios of atomic masses of target atoms and ions μ = m2/m1 were almost the same for all cases considered and greater than 1 (direct mass ratio) however, the difference of binding energies of target atoms in the cases of Cs+ and K+ scattering was almost twice as much. It has been noticed that the dependencies of the relative energy retained by scattering ions at the maximum of energy distribution versus the initial energy Em/E0 (E0) have a similar shape in all cases. The relative energy retained by scattering ions increases while the initial energy of incidence ions decreases. The curves are placed above each other relative to the binding energies of target atoms, to show what this says about the influence of binding energy on a process of scattering of low-energy ions. The correlation between value of energy change maintained by an ion for different values of E0 in the case of scattering by targets with different masses of atoms and its binding energies is experimentally established. The contrary behavior of the Em/E0 (E0) dependencies concerning the target atom binding energy quantity Eb for cases with direct (μ > 1) and inverse (μ < 1) mass ratio of colliding particles is established. The comparison of experimental energy distributions with calculated histograms shows that the binary collision approximation cannot elucidate the abnormally great shift in the maxima of relative energy distributions towards greater energy retained by scattering ions. 相似文献
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Ab initio calculations based on density functional theory have been performed to study the dissolution and migration of helium, and the stability of small helium-vacancy clusters HenVm (n, m=0-4) in aluminum. The results indicate that the octahedral configuration is more stable than the tetrahedral. Interstitial helium atoms are predicted to have attractive interactions and jump between two octahedral sites via an intermediate tetrahedral site with low migration energy. The binding energies of an interstitial He atom and an isolated vacancy to a HenVm cluster are also obtained from the calculated formation energies of the clusters. We find that the di- and tri-vacancy clusters are not stable, but He atoms can increase the stability of vacancy clusters. 相似文献
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The ratio of the chemical potential to the mean energy per π-electron is calculated in alternant molecular orbital theory for the linear polyacenes with n rings. Dimensionality appears to dominate as n→∞. Ionization potentials are also discussed for 1 ? n ? 6. 相似文献
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A nonperturbatve theory of energy losses of fast heavy multiply charged structural ions in collisions with neutral complex atoms is elaborated with allowance for simultaneous excitations of ionic and atomic electron shells. Formulas for the effective deceleration that are similar to the well-known Bethe-Bloch formulas are derived. By way of example, the energy lost by partially stripped U q+ ions (10 ≤ q ≤ 70) colliding with argon atoms and also the energy lost by Au, Pb, and Bi ions colliding with various targets are calculated. The results of calculation are compared with experimental data. 相似文献