Ionization Of Inner-shell Electrons Research Articles

The role of laser chirp in relativistic electron acceleration using multi-electron gas targets

The role of multi-10 TW chirped laser pulses interacting with N2 gas jet targets, as a test case for multi-electron targets, is experimentally examined. Complementary measurements using He gas jet targets, which are fully ionized well before the laser pulse peak, are also presented for comparison with the measurements for the multi-electron N2 targets. It is found that for both gases positively chirped laser pulses accelerate electrons more efficiently compared to the Fourier transform-limited and negatively chirped pulses. Furthermore, multi-electron targets offer additional electron injection mechanisms for efficient electron acceleration as a function of the chirp, due to the dynamic ionization of inner-shell electrons near the peak of the laser pulse. Finally, we show that the background plasma density value plays a critical role in the efficient acceleration of positively chirped pulses as well as in the tuning of the positive chirp value for maximizing the electron energy. We clearly observe that larger plasma density values require higher positive chirp values for efficient electron acceleration.

X-ray emission for Ar11+ ions impacting on various targets in the collisions near the Bohr velocity* *Project supported by the National Key R&D Program of China (Grant No. 2017YFA0402300), the National Natural Science Foundation of China (Grant Nos. 11505248, 11775042, 11875096, and 11605147) the Scientific Research Program Funded by Shaanxi Provincial Education Department, China (Grant No. 20JK0975), the Scientific Research

X-ray emission from the collisions of 3 MeV Ar11 + ions with V, Fe, Co, Ni, Cu, and Zn is investigated. Both the x-rays of the target atom and projectile are observed simultaneously. The x-ray yield is extracted from the original count. The inner-shell ionization cross section is estimated by the binary encounter approximation model and compared with the experimental result. The remarkable result is that the Ar K-shell x-ray yield is diminished with the target atomic number increasing, which is completely opposite to the theoretical calculation. That is interpreted by the competitive consumption of the energy loss for the ionization of inner-shell electrons between the projectile and target atom.

Laser-induced inner-shell excitations through direct electron re-collision versus indirect collision

The dynamics and the decay processes of inner-shell excited atoms are of great interest in physics, chemistry, biology, and technology. The highly excited state decays very quickly through different channels, both radiative and non-radiative. It is therefore a long-standing goal to study such dynamics directly in the time domain. Using few-cycle infrared laser pulses, we investigated the excitation and ionization of inner-shell electrons through laser-induced electron re-collision with the original parent ions and measured the dependence of the emitted x-ray spectra on the intensity and ellipticity of the driving laser. These directly re-colliding electrons can be used as the initiating pump step in pump/probe experiments for studying core-hole dynamics at their natural temporal scale. In our experiment we found that the dependence of the x-ray emission spectrum on the laser intensity and polarization state varies distinctly for the two kinds of atomic systems. Relying on our data and numerical simulations, we explain this behavior by the presence of different excitation mechanisms that are contributing in different ratios to the respective overall x-ray emission yields. Direct re-collision excitation competes with indirect collisions with neighboring atoms by electrons having "drifted away" from the original parent ion.

Coherent driving versus decoherent dissipation in the double inner-shell ionization of neon atoms by attosecond pulses

Exchange correlation plays an important role in double-ionization of complex atoms by ultrashort laser pulse. In this work, we investigate two-photon double inner-shell electron ionization of neon induced by an attosecond extreme ultraviolent pulse in the framework of the quantum master equation. Our simulations reveal a distinct non-sequential effect via broadened double peaks, as a result of energy sharing between the two ionized electrons. When dissipation is included to show the interplay of coherence and decoherence, the two-photon double-ionization scaling law breaks down. We further study the total cross section of $2s^2$ double ionization as a function of photon energy in both $non$-$sequential$ and $sequential$ regions.

Photodissociation investigation of doubly charged ethanol clusters induced by inner-shell electron ionization

Fragmentation of doubly charged ethanol clusters [(C(2)H(5)OH)(n)] following the O 1s ionization has been investigated by means of the photoelectron-photoion-photoion coincidence (PEPIPICO) method. The dominant fission channel of (C(2)H(5)OH)(n)(2+) was the formation of protonated cluster ion pairs [H(C(2)H(5)OH)(l)(+)/H(C(2)H(5)OH)(m)(+)]. The fragmentation mechanisms of these ion pairs were discussed based on the analysis of the PEPIPICO contour shape. It was clarified that the prominent fragmentation channel was a secondary decay mechanism, where neutral evaporation occurs after charge separation. On the other hand, the formation of small fragment ions was suppressed, excluding the formation of certain specific fragments (H(3)O(+), C(2)H(5)(+)/COH(+), and C(2)H(4)OH(+)). The formation of small fragment ions was suppressed due to the cooling effect caused by the neutral evaporation and the decrease in the electrostatic repulsive force caused by charge separation.

Calculated energy loss of swift He, Li, B, and N ions inSiO2,Al2O3, andZrO2

We have calculated the electronic stopping power and the energy-loss straggling parameter of swift He, Li, B, and N ions moving through several oxides, namely $\mathrm{Si}{\mathrm{O}}_{2}$, ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$, and $\mathrm{Zr}{\mathrm{O}}_{2}$. The evaluation of these stopping magnitudes was done in the framework of the dielectric formalism. The target properties are described by means of a combination of Mermin-type energy-loss functions that characterize the response of valence-band electrons, together with generalized oscillator strengths to take into account the ionization of inner-shell electrons. We have considered the different charge states that the projectile can have, as a result of electron capture and loss processes, during its motion through the target. The electron density for each charge state was described using the Brandt-Kitagawa statistical model and, for He and Li ions, also hydrogenic orbitals. This procedure provides a realistic representation of both the excitation properties of the target electrons and the projectile charge density, yielding stopping powers that compare reasonably well with available experimental data above a few tens of keV/amu.

Dynamics of ionization mechanisms in relativistic collisions involving heavy and highly-charged ions

The dynamics of mechanisms associated with the ionization of inner-shell electrons in relativistic collisions involving heavy and highly-charged ions is investigated within a nonperturbative approach formulated explicitly in the time domain. The theoretical treatment is based on the exact numerical solution of the time dependent Dirac equation for two Coulomb centers on a lattice in momentum space. We present results for ionization in encounters between 100 MeV/u Au79+ projectile ions impinging on a hydrogen-like uranium target. By directly visualizing the collision dynamics we identify a new ionization mechanism in which electrons are emitted from the internuclear region preferentially in the transverse direction with respect to the projectile trajectory. A striking characteristic of this ionization mechanism is that the velocity of the electron is higher than the projectile velocity.

70 years of Auger spectroscopy, a historical perspective

The discovery of the nonradiative decay of an inner-shell ionized atom by the emission of an electron was made by P. Auger in 1925. The first investigation of Auger electrons by means of a magnetic electron spectrograph was done by Robinson and Cassie in 1926, this marks the birth date of Auger spectroscopy. The following 70 years of Auger spectroscopy of atoms will be divided into three periods. In the first period (1926–1960; Section 2) Auger spectroscopy was mainly connected with β-ray spectroscopy where inner-shell ionization in atoms in the solid state was caused either by γ-conversion or by electron capture. In the second period (beginning in 1960; Section 3) Auger spectroscopy developed independently of the availability of radioactive sources by using external excitation of gaseous atomic or metal vapor targets. The third period (beginning in 1977/78; Section 4) is characterized by the use of synchrotron radiation with its outstanding properties of tunability, polarization and narrow-band high-intensity for the excitation and ionization of inner-shell electrons.

(e,2e) experiments with spin-polarized electrons

Recent experimental work on (e,2e) coincidences involving polarized electrons is reviewed. The origin of the observed spin asymmetries are exchange effects, spin-orbit interaction of the continuum electrons, and spin-orbit coupling within the target in conjunction with orbital orientation and exchange. These mechanisms are explained in some detail. Experimental and theoretical investigations of spin effects have been performed for ionization of outer shell electrons as well as for ionization of inner shell electrons.

A measurement of the cross section for electron impact ionization of Ar2+, Kr2+ and Xe2+

The crossed electron-ion beams technique was used to measure absolute cross sections for single ionization of Ar2+, Kr2+ and Xe2+ ions at electron energies ranging from threshold to 2000 eV. The total error in the cross sections at a 90% confidence level is estimated to be +or-4.8, +or-4.9 and +or-7% or less for Ar2+, Kr2+ and Xe2+ respectively, at energies more than a few electron volts above threshold. In contrast to some previous measurements, the metastable contents of the ion beams were small even in the case of Xe2+. All measured cross section curves show significant contributions from excitation-autoionization and possibly direct ionization of inner-shell electrons. There is evidence for resonance-excitation-double-autoionization in the case of Xe2+. Comparisons are made with other available experimental and theoretical data.

Applications of a direct simulation of electron scattering to quantitative electron-probe microanalysis

A direct simulation of electron scatterings in solids is developed. The simulation takes into account elastic processes, and inelastic processes including inner-shell electron ionization, conduction electron ionization, bulk plasmon excitation, and bulk plasmon decay. After the ionization and the plasmon decay processes, the trajectories of hot electrons which are liberated from atomic electrons are calculated, and cascade multiplication of hot electrons is simulated in the solid. The theoretical equations used in the present simulation are in the following. For the elastic scattering of electrons by an atomic potential, we use the Mott cross section, which is obtained by the partial wave expansion method of the solution of the Dirac wave equation. For the inner-shell electron ionization, we use the cross section obtained from the generalized oscillator strength for each sub-shell in an atom. Under a condition of the Born approximation, cross section of an inner-shell electron excitation to the various continuum angular momentum channels for ionization is calculated using the generalized oscillator strength.

The measurement of inner-shell ionization cross aections by electron impact in a TEM

Values of cross sections for ionization of inner-shell electrons by electron impact are required for electron probe microanalysis, Auger-electron spectroscopy and electron energy-loss spectroscopy. In this work, the results of the measurement of inner-shell ionization cross-sections by electron impact, Q, in a TEM are presented for the K shell.The measurement of QNi has been performed at 120 KeV in a TEM by measuring the net X-ray intensity of the Kα line of Ni, INi, which is related to QNi by the relation :(1)where i is the total electron dose, (Ω/4π)is the fractional solid angle, ω is the fluorescence yield, α is the relative intensity factor, ε is the Si (Li) detector efficiency, A is the atomic weight, ρ is the sample density, No is Avogadro's number, t' is the distance traveled by the electrons in the specimen which is equal to τ sec θ neglecting beam broadening where τ is the specimen thickness and θ is the angle between the electron beam and the normal of the thin foil and CNi is the weight fraction of Ni.

A Simulation of Electron Scattering in Metals

A Monte Carlo calculation model is developed to simulate trajectories of primary and ionized electrons in metals. It is constructed especially for a quantitative analysis of images in the scanning electron microscope. We perform a direct simulation considering each differential scattering cross section for elastic scattering, inner-shell electron ionization, conduction band electron ionization and bulk plasmon excitation. The spatial distribution of secondary electron emission calculated is narrower than that of backscattered electron emission at the Al surface for 1 keV primary electrons, but depending on the condition, this tendency may not always be found. The spatial distributions of both secondary and backscattered electrons show the size effect, and if the specimen to be observed is smaller, the practical resolution will be better in the scanning electron microscope.

A Simulation of Electron Scattering in Metals and its Application for Scanning Electron Microscopy

In a recent research, the scanning electron microscope(SEM) has been shown to provide spatial resolution of less than 0.5nm. With the knowledge of the ultimate resolution or the factor which controls the resolution, it is possible to optimize the specimen preparation method and the choice of various electron beam parameters (eg. acceleration voltage etc.) For a precise discussion of the SEM image, it is necessary to take into account not only the signal (electron) production and the propagation in a specimen and its emission from the surface, but also electron trajectories in vacuum toward the detector. However, electron scattering process in the specimen does not depend on the detection system, and the resolution is mainly attributed to the spatial distribution of the electron emission from the specimen surface. Here, we focused on the electron scattering mechanisms in metals and developed a Monte Carlo simulation model of electron trajectories. Also, this simulation is applied to evaluate a compositional contrast in the SEM.In the present study electron interactions with atomic potential, inner-shell electrons, conduction electrons are taken into account. Cross sections calculated by the present model are shown in Fig.1 for [l]elastic scattering, [2]inner-shell (1s, 2s, 2p for Al) electron ionization, [3]conduction electron ionization through non-radiative plasmon decay, and [4] stable plasmon excitation in the conduction band electrons for Al. For the elastic scattering, the Mott cross section is used. For inner-shell electron ionizations by an electron collision, the Gryzinski equation is used. In order to express the plasmon-electron interaction in a free electron gas at the conduction band, the Lindhard treatment is used. This treatment is based on the random phase approximation in the dielectric response function of metals. The cross section is shown in a unit of the inverse mean free path. The cross sections for conduction electron ionization and the plasmon excitation agree with the data of Tung, Ashley, and Ritchie. Cross sections for inner-shell electron ionization, which Tung et al. have derived using the generalized oscillator strength, are also shown in Fig.1 for a comparison.

Inner-Shell Ionization Cross Sections

Values of cross sections for ionization of inner-shell electrons by electron impact are required for electron probe microanalysis, Auger-electron spectroscopy, and electron energy-loss spectroscopy. The present author has reviewed measurements and calculations of inner-shell ionization cross sections. This paper is an update and summary of these previous reviews.It is convenient to start with the Bethe equation for inner-shell ionization cross sections which is frequently used (and misused) in x-ray microanalysis:(1)where σnℓ is the cross section for ionization of the nℓ shell with binding energy Enℓ by incident electrons of energy E. The terms bnℓ and cnℓ are the Bethe parameters discussed further below. It has been assumed in the derivation of Eq. (1) that E ≫ Enℓ ; this requirement will also be discussed. Finally, it has been assumed here that E is low enough (≲50 keV) so that a relativistic correction is unnecessary.The extent to which a given set of measured or calculated cross-section data is consistent with Eq. (1) can be determined from a Fano plot in which σnℓE is plotted versus ℓnE; if such a plot is linear, Eq. (1) is consistent with the data and values of the Bethe parameters can be easily derived.

Vicinage effect in inner-shell ionization.

The vicinage effect in the double ionization of inner-shell electrons has been calculated using first-order perturbation theory. Calculations demonstrate that significant differences arise when the orthogonalized hole in the electron gas is properly taken into account. Comparison with previous calculations by Basbas and Ritchie (Phys. Rev. A 25, 1943 (1982)) and experimental data is made.

Multiple ionization and x-ray line emission resulting from inner-shell electron ionization.

We report an application of our previously developed model for determining the probabilities P(${\ensuremath{\alpha}}_{N}$,${N}_{A}$) of emitting ${N}_{A}$ Auger electrons and the probabilities P(${\ensuremath{\alpha}}_{N}$,${\ensuremath{\beta}}_{N}$\ensuremath{\rightarrow}${\ensuremath{\gamma}}_{N}$) of the radiative transitions ${\ensuremath{\beta}}_{N}$\ensuremath{\rightarrow}${\ensuremath{\gamma}}_{N}$ during the cascade decay process following the creation of an arbitrary distribution ${\ensuremath{\alpha}}_{N}$ of N vacancies among the nl subshells of an atomic system. Particular emphasis has been given to the effects of single inner-shell vacancies, which may be created by energetic charged-particle collisions or by x-ray photoionization. Results of calculations are presented for single inner-shell electron ionization of iron ions from the neutral atom through the heliumlike ionization state, taking into account all of the Auger, Coster-Kronig, and electric dipole radiative transitions which can occur during the inner-shell vacancy-cascade process. The importance of the multiple ionization which results from Auger electron emission and of the x-ray satellite line radiation which is produced by the radiative decay of multiple-vacancy states is investigated for inner-shell electron ionization by electron collisions and by photon impacts.

Ionization by H +2. Molecular effect

The molecular effect in the ionization of inner shell electrons of aluminum atoms by energetic H + 2 molecules has been calculated. We distinguish between the molecular effect in Al and Al 2O 3. We conclude that in the case of Al the protons of the cluster have a definite orientation but in the case of Al 2O 3 the orientation is at random.

Probability of internal ionization duringβ+decay: Importance of the direct-collision mechanism

A theory of the ionization of inner-shell electrons during ${\ensuremath{\beta}}^{+}$ decay is obtained by modifying a theory of inner-shell ionization during ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay presented previously. The theory includes the contributions of both the shakeoff and direct-collision mechanisms and yields results whose relative accuracy is of order $Z\ensuremath{\alpha}$. Numerical results for the $K$-shell ionization probability are presented for several nuclides, including $^{58}\mathrm{Co}$, $^{64}\mathrm{Cu}$, and $^{65}\mathrm{Zn}$; they demonstrate that, contrary to the ${\ensuremath{\beta}}^{\ensuremath{-}}$ case, the direct-collision mechanism plays an essential role in inner-shell ionization during ${\ensuremath{\beta}}^{+}$ decay, confirming a conjecture by Law. When compared with the results of recent experiments, they are found to give significantly better agreement than do the results of previous theoretical work.

Inner-shell ionization during nuclearβdecay

A theory is developed of the ionization of inner-shell electrons during ..beta.. decay. For allowed transitions it is shown that in the lowest order of the coupling constants the transition amplitude for the process is a sum of two terms, one of which attributes the ionization process to the sudden change in nuclear charge, and the other to a virtual scattering of an inner-shell electron by the emerging ..beta.. particle. For the K-shell-specific calculations are carried out using nonrelativistic hydrogenic wave functions and a Coulomb Green's function due to Glauber and Martin. Results whose relative accuracy is of order Z..cap alpha.. are obtained for energy spectra, angular correlation functions, and the total internal ionization probability; numerical results are presented for the nuclides /sup 63/Ni, /sup 107/Pd, and /sup 151/Sm. The role of the virtual-scattering mechanism is assessed and a comparison with other recent theoretical work is made.