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1.
We study the double ionization of the atomic K-shell by a single photon in the relativistic energy domain. The differential and total cross sections of the process are
calculated. It is shown that the ratio of the cross sections of double and single ionization increases with the photon energy,
tending to the limit 0.34/Z
2, where Z is the atomic number or the nuclear charge. The formulas are found to be valid for Z≫1 and αZ≪1, where α=1/137 is the fine-structure constant.
Zh. éksp. Teor. Fiz. 114, 1537–1554 (November 1998) 相似文献
2.
A. I. Mikhailov A. V. Nefiodov G. Plunien 《Journal of Experimental and Theoretical Physics》2009,109(5):762-769
We evaluate the total cross section for the single K-shell ionization of atoms and ions by the impact of relativistic electrons.
The study is performed to leading orders of the QED perturbation theory with respect to the parameters αZ and 1/Z. The results obtained are in good agreement with experimental data for different atomic targets. In the case of moderate
values of the nuclear charge Z, the total cross section is described by a simple analytic formula. The K-shell ionization by relativistic heavy particles
is also considered. 相似文献
3.
A. B. Voitkiv 《Technical Physics》1998,43(3):265-270
Expressions for the cross sections for single and double ionization of atomic helium in collisions with fast multiply charged
ions are obtained in the collision parameter range υ
2≫Z≳υ, υ
0<c, where Z and υ are, respectively, the ion charge and ion velocity, υ
0 is the characteristic velocity of electrons in the atomic helium ground state, and c is the velocity of light.
Zh. Tekh. Fiz. 68, 1–7 (March 1998) 相似文献
4.
We study the annihilation of a fast positron and a K-electron resulting in the emission of a photon and a second K-electron. It is assumed that all electrons and positrons move in the Coulomb field of the nucleus and that the Coulomb parameter
αZ is much less than unity (α=1/137 is the fine-structure constant and Z is the atomic number). The electron-electron interaction, which is responsible for the ejection of the electron by the atom,
is taken into account in the first order of perturbation theory. We calculate the differential and total cross sections of
the process and construct the ratio of the cross sections of double and single ionization as a function of the energy of the
incident positron. Finally, we establish the high-energy limit of this ratio, equal to 0.34/Z
2.
Zh. éksp. Teor. Fiz. 113, 786–804 (March 1998) 相似文献
5.
K-shell ionization cross section measurements are reported for35Br,37Rb and39Y targets caused by protons over 300–400 keV energy range in 20 keV increment. The K-shell ionization cross sections (σ
k
l
) at different energies were deduced from the Kα and Kβ X-ray production cross sections which were obtained from X-ray yields of the Kα and Kβ transitions. The experimental values are compared with the calculated values of ECPSSR theory and empirical reference cross
sections. The resultant K-shell ionization cross sections are found to be in reasonable agreement with the ECPSSR theory.
The Kα/Kβ intensity ratios are also presented and compared with other experimental values and also with the theoretical one-hole values
given by Scofield. 相似文献
6.
A. B. Voitkiv 《Journal of Experimental and Theoretical Physics》1997,85(6):1074-1080
Ionization of hydrogen and helium atoms is studied for the case of “soft” collisions with highly charged fast ions with v≲Z≪v2 and v≫v
0, where Z is the ion charge, v is the collision velocity, and v
0∼1 is the characteristic velocity of the electron in the ground state of the atom. Analytical expressions are derived for
the singly and doubly differential cross section for ionization of a hydrogen atom accompanied by the ejection of a slow electron
v
e≲v
0, where v
e is the velocity of the ejected electron with respect to the recoil ion). The results are generalized to the case of single
ionization of helium. It is shown that soft collisions provide the main contribution to the hydrogen ionization cross section
and for all practical purposes determine the cross section for single ionization of helium. The asymmetry in the angular distribution
of the ejected slow electrons and the properties of momentum exchange in such collisions are discussed. Finally, a formula
for the cross section for single ionization of helium is proposed.
Zh. éksp. Teor. Fiz. 112, 1966–1977 (December 1997) 相似文献
7.
The probability w
L
of Lorentzian ionization, which arises when an atom or ion moves in a constant magnetic field, is calculated in the quasiclassical
approximation. The nonrelativistic (v≲e
2/ℏ=1, v is the velocity of the atom) and ultrarelativistic (v→c=137) cases are examined and the stabilization factor S, which takes account of the effect of the magnetic field on tunneling of an electron, is found.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 391–396 (10 March 1997) 相似文献
8.
Multiphonon ionization of the H2 molecule under the action of a weak (probe) field, which provides the initial population of the low-lying (working) level,
and intense monochromatic linearly polarized radiation is studied. The multiphoton ionization process occurs under the conditions
of strong field perturbation of two intermediate Rydberg series, np0(1Σ
u
+
and np2(1Πu), of the optical R(0)branch which have different ionization potentials. The series are occupied simultaneously as a result of single-photon
absorption by an excited H
2
*
molecule in the working state 4s
σH′1Σ
g
+
(v=0). As a result of the irregularity in the arrangement of the intermediate levels from a large group of states that are combined
in the multiphoton ionization process a sharp and irregular change occurs in the dependence of the shifts and widths Γn of the levels on the intensity f of the strong field in a transition from one level to another. It is shown that for field intensities f such that the level widths remain much less than the splitting between the levels (Γn≪/n
3) the stabilizing effect (i.e., the field-induced narrowing of the levels as f→∞) in the form Γn ∝ 1/f
2 (as happens in atoms with a structureless core) is not observed in molecular systems.
Zh. éksp. Teor. Fiz. 115, 1987–2000 (June 1999) 相似文献
9.
Using the semiclassical Green’s function in the Coulomb field, we analyze the probabilities of single and multiple e
+
e
− pair production at a fixed impact parameter b between colliding ultrarelativistic heavy nuclei. We perform calculations in the Born approximation with respect to the parameter
Z
Bα and exactly in Z
Aα, where Z
A and Z
B are the charge numbers of the corresponding nuclei. We also obtain the approximate formulas for the probabilities valid for
Z
Aα, Z
Bα ≲ 1.
The text was submitted by the authors in English. 相似文献
10.
An analysis is made of the ionization of deep impurity centers by high-intensity far-infrared and submillimeter-wavelength
radiation, with photon energies tens of times lower than the impurity ionization energy. Within a broad range of intensities
and wavelengths, terahertz electric fields of the exciting radiation act as a dc field. Under these conditions, deep-center
ionization can be described as multiphonon-assisted tunneling, in which carrier emission is accompanied by defect tunneling
in configuration space and electron tunneling in the electric field. The field dependence of the ionization probability permits
one to determine the defect tunneling times and the character of the defect adiabatic potentials. The ionization probability
deviates from the field dependence e(E) ∝ exp(E
2/E
c
2
) (where E is the wave field, and E
c is a characteristic field) corresponding to multiphonon-assisted tunneling ionization in relatively low fields, where the
defects are ionized through the Poole-Frenkel effect, and in very strong fields, where the ionization is produced by direct
tunneling without thermal activation. The effects resulting from the high radiation frequency are considered and it is shown
that, at low temperatures, they become dominant.
Fiz. Tverd. Tela (St. Petersburg) 39, 1905–1932 (November 1997) 相似文献
11.
Thomas Simon 《Journal of statistical physics》2008,131(4):733-747
Consider an inviscid Burgers equation whose initial data is a Lévy α-stable process Z with α>1. We show that when Z has positive jumps, the Hausdorff dimension of the set of Lagrangian regular points associated with the equation is strictly
smaller than 1/α, as soon as α is close to 1. This gives a partially negative answer to a Conjecture of Janicki and Woyczynski (J. Stat. Phys. 86(1–2):277–299,
1997). Along the way, we contradict a recent Conjecture of Z. Shi () about the lower tails of integrated stable processes. 相似文献
12.
Amplified spontaneous inner-shell emission produced via an ultrafast burst of high-energy electrons from a femtosecond laser-produced
plasma is proposed as a novel electron-pumped x-ray laser. In this scheme, a population inversion of the upper laser level
is created via impact ionization of atomic inner shells by electron bombardment. Based on the requirement of a positive gain
coefficient for amplifying spontaneous K
α
line emission, a simple pumping threshold is found for the incident electron flux, and feasibility of the scheme is assessed
for a range of low-Z elements.
Published in English in the original Russian journal. Edited by Steve Torstveit.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 771–776 (25 May 1998) 相似文献
13.
We study zero-temperature, stochastic Ising models σ
t
on Z
d
with (disordered) nearest-neighbor couplings independently chosen from a distribution μ on R and an initial spin configuration chosen uniformly at random. Given d, call μ type ℐ (resp., type ℱ) if, for every
x in Z
d
, σ
x
t
flips infinitely (resp., only finitely) many times as t→∞ (with probability one) – or else mixed type ℳ. Models of type ℒ and ℳ exhibit a zero-temperature version of “local non-equilibration”.
For d=1, all types occur and the type of any μ is easy to determine. The main result of this paper is a proof that for d=2, ±J models (where μ=αδ
J
+(1-α)δ-
J
) are type ℳ, unlike homogeneous models (type ℐ) or continuous (finite mean) μ's (type ℳ). We also prove that all other noncontinuous
disordered systems are type ℳ for any d≥ 2. The ±J proof is noteworthy in that it is much less “local” than the other (simpler) proof. Homogeneous and ±J models for d≥ 3 remain an open problem.
Received: 3 November 1999 / Accepted: 10 April 2000 相似文献
14.
We derive a closed relativistic expression that makes it possible to calculate the self-energy of multiply charged ions in
an external Coulomb field without resorting to a series expansion in powers of αZ. The expression contains the generalized Bethe logarithm for tightly bound electrons. We do numerical calculations of the
self-energy for the 1s
1/2-electrons of multiply charged hydrogenlike ions. The proposed method allows for self-energy calculations for any values of
the nuclear charge Z.
Zh. éksp. Teor. Fiz. 112, 1197–1208 (October 1997) 相似文献
15.
We consider a large neutral molecule with total nuclear charge Z in non-relativistic quantum mechanics with a self-generated classical electromagnetic field. To ensure stability, we assume that Z α 2 ≤ κ 0 for a sufficiently small κ 0, where α denotes the fine structure constant. We show that, in the simultaneous limit Z → ∞, α → 0 such that κ = Z α 2 is fixed, the ground state energy of the system is given by a two term expansion c 1 Z 7/3 + c 2(κ) Z 2 + o(Z 2). The leading term is given by the non-magnetic Thomas-Fermi theory. Our result shows that the magnetic field affects only the second (so-called Scott) term in the expansion. 相似文献
16.
R. R. Silva L. A. Vieira Mendes K. H. Tsui R. A. De Simone Zanon A. L. de Oliveira C. E. Fellows 《Applied physics. B, Lasers and optics》2011,104(3):679-687
Nitrogen laser performance with TE configuration and wedge electrodes is analyzed with background ionization in the laser
discharge channel by α particles at a low exposition rate. With the bias ionization, the laser power presents two peaks as a function of gas pressure,
with one at the normal low pressure, without bias ionization, and the other at high pressure generated by bias ionization.
A simple theoretical model has been developed in a trial to understand this behavior. This model was first tested in later
results for a TE configuration nitrogen laser, with flat electrodes, without and with bias ionization. It has been observed
that due to the competition between electrode shielding by positively charged α particles and bulk ionization by impact, the laser energy is suppressed with pressure below 50 Torr and enhanced above it. 相似文献
17.
A. G. Leonov D. I. Chekhov A. N. Starostin 《Journal of Experimental and Theoretical Physics》1997,84(4):703-715
An experimental investigation and numerical simulation of resonant laser breakdown are performed. As a result, quantitative
agreement between the experimental data on the parameters of a dense resonant plasma (the electron density and the electron
temperature) and the results of calculations in the range of detunings of the laser radiation from resonance Δλ>2–2.5 nm, in which the spatial instability of the intense resonant laser beam and the absorption of radiation are minimal,
is obtained for the first time. It is shown that the previously proposed mechanism of resonant breakdown associated with laser-induced
associative ionization introduces only a small correction to the final extent of ionization of the resonant plasma and scarcely
alters its temperature. The influence of quantum stimulated inverse bremsstrahlung processes, which are usually described
as collisions of the second kind in the resonance case, on the energy gain by electrons is analyzed for the first time in
reference to specific experimental findings. The numerical calculations show that at detunings of the order of the Rabi frequency,
the mechanism by which electrons gain energy through the resonant system does not reduce to collisions of the second kind
and can significantly increase the density of the resonant plasma. However, in this range of detunings the laser beam is still
strongly perturbed by instability processes, precluding a proper comparison of the theory with experiment. At large Δλ the classical and quantum cases differ from one another only slightly, and the values of N
e calculated for both mechanisms lie within the measurement error.
Zh. éksp. Teor. Fiz. 111, 1274–1296 (April 1997) 相似文献
18.
《X射线光谱测定》2005,34(1):64-68
Electron shakeup and shakeoff probabilities accompanying inner‐shell ionization of atoms were calculated for K‐, L‐ and M‐shell electrons using hydrogenic wavefunctions. The dependence of shake probabilities on atomic number Z is estimated. It is found that both shakeoff and shakeup probabilities are proportional to 1/Z2. Based on this Z‐dependence, the shakeup‐plus‐shakeoff probabilities are expressed in a simple analytical form with two parameters. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
19.
W. von Oertzen 《The European Physical Journal A - Hadrons and Nuclei》2006,29(2):133-139
The systematics for binding energies per α-particle in N = Z nuclei, E
Bα/N
α, are studied up to 164Pb. It is shown that, although a geometrical model can be used to explain the systematics for light nuclei, the binding energy
per α-particle exhibits structures which are due to the well-known shells of the mean field of nucleons in nuclei. The overall
dependence of E
Bα/N
α on N
α in N = Z nuclei (for the ground-state masses) can be described in a liquid-drop model of α-particles. Conditions for a phase change
with the formation of an α-particle condensate, a dilute Bose gas in excited compound nuclei are discussed for E
Bα/N
α = 0, at the thresholds. This is achieved when the binding energy per nucleon in nuclei is equal to or smaller than in the
α-cluster. At somewhat smaller excitation energies the appearance of a Bose gas with a closed-shell core (N = Z, e.g. of 40Ca) is proposed within the same concept. The experimental observation of the decay of such condensed α-particle states is
proposed with the coherent emission of several correlated α-particles not described by the Hauser-Feshbach approach for compound-nucleus
decay. This decay will be observed by the emission of unbound resonances in the form of 8Be and 12C * (0+
2) clusters. 相似文献
20.
We consider a large atom with nuclear charge Z described by non-relativistic quantum mechanics with classical or quantized electromagnetic field. We prove that the absolute
ground state energy, allowing for minimizing over all possible self-generated electromagnetic fields, is given by the non-magnetic
Thomas-Fermi theory to leading order in the simultaneous Z → ∞, α → 0 limit if Z
α
2 ≤ κ for some universal κ, where α is the fine structure constant. 相似文献