共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
Thana Maihom Ivan Sukuba Ratko Janev Kurt Becker Tilmann Märk Alexander Kaiser Jumras Limtrakul Jan Urban Pavel Mach Michael Probst 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2013,67(1):1-5
We report calculated electron impact ionization cross sections (EICSs) for beryllium (Be) and some of its hydrides from the ionization threshold to 1 keV using the Deutsch-Märk (DM) and the Binary-Encounter-Bethe (BEB) formalisms. The positions of the maxima of the DM and BEB cross sections are very close in each case while the DM cross section values at the maxima are consistently higher. Our calculations for Be are in qualitative agreement with results from earlier calculations (convergent close-coupling, R matrix, distorted-wave and plane-wave Born approximation) in the low energy region. For the various beryllium hydrides, we know of no other available data. The maximum cross section values for the various compounds range from 4.0 × 10?16 to 9.4 × 10?16 cm2 at energies of 44 to 56 eV for the DM cross sections and 3.0 × 10?16 to 5.4 × 10?16 cm2 at energies of 40.5 to 60 eV for the BEB cross sections. 相似文献
3.
Phonon frequencies in beryllium along the principal symmetry directions have been determined by means of the slow neutron
inelastic scattering technique. The data are analysed in terms of a six-neighbour force constant model and the force constants
are evaluated. It is concluded that strong tensor forces are present in beryllium and the importance of this finding to basic
theories of lattice dynamics is pointed out. 相似文献
4.
M.V. Ivanov P. Schmelcher 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):279-288
The ground and a few excited states of the beryllium atom in external uniform magnetic fields are calculated by means of our
2D mesh Hartree-Fock method for field strengths ranging from zero up to 2.35×109 T. With changing field strength the ground state of the Be atom undergoes three transitions involving four different electronic
configurations which belong to three groups with different spin projections S
z = 0, - 1, - 2. For weak fields the ground state configuration arises from the 1s
22s
2, S
z = 0 configuration. With increasing field strength the ground state evolves into the two S
z = - 1 configurations 1s
22s2p
-1 and 1s
22p
-13d
-2, followed by the fully spin polarised S
z = - 2 configuration 1s2p
-13d
-24f
-3. The latter configuration forms the ground state of the beryllium atom in the high field regime γ > 4.567. The analogous
calculations for the Be
+ ion provide the sequence of the three following ground state configurations: 1s22s and 1s
22p
-1 (S
z = - 1/2) and 1s2p
-13d
-2 (S
z = - 3/2).
Received 2 October 2000 and Received in final form 8 January 2001 相似文献
5.
JoséM.P. Serrão 《Journal of Quantitative Spectroscopy & Radiative Transfer》1985,33(3):219-226
Energy terms, dipole oscillator strengths and photoionization cross-sections from the ground state are calculated. Autoionizing state transition energies and line widths for the 1P0 resonances in the continuum are also obtained. The configuration interaction method for initial and final states is used, and atomic orbitals are generated through angular-momentum-dependent, scaled Thomas-Fermi-Dirac potentials. 相似文献
6.
The band structure of body-centered cubic beryllium is reported, both at the Hartree and exact-exchange Hartree-Fock level. There is no gap immediately above the valence band. This is consistent with the resistivity experiments by Amonenko et al. which rises sharply, but not discontinuously above the h.c.p.-to-b.c.c. phase transition at 1254°C. 相似文献
7.
Creep characteristics of beryllium have been determined in the temperature range 600–800°C and the stress range 0.25–5 kgf/mm2. The rate of the process is controlled by the Herring —Nabarro mechanism in the range of stresses less than 1 kgf/mm2. The creep activation energy (39±1 kcal/mole) hence agrees with the energy of self-diffusion. The creep rate for stresses greater than 1 kgf/mm2 is determined by the simultaneous progress of dislocation creep and slip, where the slip contribution grows with the increase in stress. An approximate picture of the deformation mechanisms of creep is constructed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 68–73, March, 1976. 相似文献
8.
Gilman's criterion erroneously predicts the most probable cleavage plane of Be. The formula is refined in order to take into account anisotropy of the interaction range between atoms in various planes. The pseudopotential approximation is used, and the cleavage plane is now correctly predicted. 相似文献
9.
A. V. Popov 《Physics of the Solid State》2008,50(8):1592-1596
10.
Using the modified Feshbach method, the1,3Se,1,3Po,1,3De,1,3So autoionization states of the beryllium atoms are calculated in the region of the first ionization threshold. The energies and widths of the autoionization states of Be are obtained. The results obtained are compared with experimental data and the results of existing theoretical calculations. The good agreement between the results obtained and the experimental data and other theoretical calculations is pointed out.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 23–28, March, 1984. 相似文献
11.
The theory of the electronic excitations in a highly excited semiconductor is presented. The relaxation processes, the formation of excitons and excitonic molecules, the interaction among the various forms of electronic excitations, as well as their optical and thermodynamical properties are analyzed. At low temperatures one expects condensations into the quantum statistically degenerate phases of the excitonic molecules and of the electron-hole plasma. The physical properties of these low temperature phases are investigated. Possibilities and previous attempts to observe the Bose-Einstein condensation in excitonic systems are discussed critically. The experimental observations of the electron-hole liquid phase transition are reviewed. 相似文献
12.
Techniques due toR. L. Dobrushin andR. Griffiths are combined to prove the existence of a first order phase transition at low temperature for a class of lattice systems with non nearest-neighbour interaction. 相似文献
13.
V. S. Egorov E. P. Krasnoperov F. V. Lykov U. Zimmermann G. Solt C. Baines D. Herlach 《Physics of the Solid State》1998,40(3):482-484
We have observed diamagnetic domains (Condon domains) in a beryllium single crystal in magnetic fields H⩽3 T (H∥[0001]) at liquid-helium temperatures. The formation of the domain structure was determined according to magnetic-breakdown
quantum oscillations of the resistance thermoelectric power as well as according to the splitting of the resonance peak of
the free spin precession frequency of muons (μSR). The alternation of a uniform state (with one μSR peak) and a state with
domain structure (with two peaks) is consistent as regards the periodicity with the de Haas-van Alphen effect, the period
is ΔH≅78 Oe, and the range of existence of domains and the difference in their magnetizations are ΔB=4πΔM=B
2−B
1≅30 Oe.
Fiz. Tverd. Tela (St. Petersburg) 40, 524–526 (March 1998) 相似文献
14.
The defocussing and the depolarization of a high energy muon beam in a beryllium filter, often used to eliminate accompanying
pions, have been studied. The quantum mechanical transport equation of Waldmann, which can also be used to describe the multiple
scattering of Dirac particles, is solved with a distorted wave Born approximation. Calculations are done for both the Thomas-Fermi
and the Hartree-Fock potential of the beryllium atom. It is shown that the Hartree-Fock potential leads to a less divergent
beam. The depolarization of a longitudinally polarized muon beam in passage through a thin beryllium foil is also studied. 相似文献
15.
J.A. Leiro 《Solid State Communications》1982,41(1):97-98
The threshold exponents related to the singularities in the X-ray spectra of solid beryllium has been calculated using a nonseparable scattering potential. An appreciable d-wave contribution is obtained. 相似文献
16.
Hasegawa S Yoshida F Matsuoka L Koike F Fritzsche S Obara S Azuma Y Nagata T 《Physical review letters》2006,97(2):023001
We have observed K-shell and L-shell hollow beryllium atoms (2s(2)2p3s and 1s3s(2)3p) created by photoexcitation using synchrotron radiation. Resonance shapes were fitted to the Fano profile and the parameters were deduced. A Dirac-Fock calculation was performed to identify the configuration of the peaks and to predict other hollow atomic peaks. The results of the calculation were in good agreement with the experimental data. The comparison of the transition strength has revealed that the three-electron photoexcitation to the 1s3s(2)3p configuration is stronger than the two-electron photoexcitation to the 2s(2)2p3s configuration. This is attributed to the large overlap between the 2s orbital of the ground state (1s(2)2s(2)) with the orbital of the L-shell hollow state (1s3s(2)3p). 相似文献
17.
V. E. Varlamov V. V. Nesvizhevskii A. P. Serebrov R. R. Tal’daev A. G. Kharitonov P. Geltenbort Ts. Ts. Panteleev A. V. Strelkov V. N. Shvetsov M. Pendlebury K. Schreckenbach 《Journal of Experimental and Theoretical Physics》1998,87(3):426-432
The temperature dependence of the loss factor for ultracold neutrons owing to heating at thermal energies on the surface of
a beryllium sample is studied. The probability of heating ultracold neutrons is anomalously high throughout the entire measured
temperature interval, but especially at low temperatures.
Zh. éksp. Teor. Fiz. 114, 786–797 (September 1998) 相似文献
18.
The channelling of protons through a thin beryllium crystal is simulated in a computer. The angular dependence of the momentum
density is computed using particle trajectory approximation and is reported as the transmission spectra. In obtaining the
spectra, the energy loss suffered by protons due to electron multiple scattering is considered and the effect of thermal vibrations
treated separately. The spectra obtained are characteristic of the hcp structure of Be. Positions of the major dips in the
transmission spectra are found to correlate well with the directions of neighbouring strings. Variations in the angle of incidence
of the beam and in its initial azimuthal angle bring about modifications in the spectra depending on the transverse kinetic
energy of the incident particles and the crystalline structure of Be. Thermal vibration of the lattice does not modify the
spectra appreciably. 相似文献
19.
An analysis of the electronic structure in beryllium slabs with an ab initio LCAO HF method is presented. Band structure, electronic density and density of states were determined for thin films of 1 to 4 atomic layers of Be. A comparison of the electronic structure in films of different thickness with the situation found for bulk Be and Be clusters shows strong modifications in the surface region and a progressive reconstruction of the bulk bonds. 相似文献
20.
Beryllium oxide in the forms of either single crystals (pristine, additively-colored) or hot-pressed ceramic samples was studied in the energy range of 1.2–6.2 eV using both the thermoluminescence (TL) and steady-state X-ray induced luminescence (XRL) techniques. The XRL emission spectra were recorded at 6 and 293 K, whereas TL glow curves were studied after X-ray exposure at T0 = 6 K upon linear heating in the temperature range from 6 to 293 K. A search for TL manifestations of shallow trapping centers was carried out using a sensitive channel for TL registration in the range of more than six decades of change in intensity. The participation of shallow trapping centers in the process of recombination luminescence excitation at 6–293 K; branching electronic excitations between different recombination channels; the dominance of the self-trapped exciton and F-center emissions in spectra of the low-temperature recombination luminescence in BeO at 6–293 K were discussed. 相似文献