Photoionization Cross Sections Research Articles

On the development of relativistic distorted wave approximation for the energies and collision dynamics of atoms or ions subjected to the outside plasma

In this manuscript, we present the development of a relativistic distorted wave method for determining the energies and collision dynamics of plasma-immersed atoms or ions. The methodology is based on the Dirac–Coulomb Hamiltonian, in which contributions from relativity and higher order effects, such as quantum electrodynamics and Breit interaction, are incorporated. The key element in this method is that a modified Debye–Hückel approximation is employed to represent the effect of plasma screening. In order to correctly describe the (bound and continuous state) wave functions, a self-consistent field calculation incorporating the shielding potential is performed within the fully relativistic framework. The particle interaction within the scattering matrix element of the excitation process is described by the shielded Coulomb interaction. The present technique is illustrated by calculations of energy, line shift, transition probability, electron-impact excitation/ionization cross section, and photoionization cross section of a few-electron system confined in plasma environments. The present model is tested and validated against a number of known cases (simulations are made for the He-like Al11+ ion) in the literatures. Numerical results demonstrate that the modifications to the Coulomb potential proposed in the spatial and temporal criteria of the Debye–Hückel approximation allow us to improve the theoretical description of the plasma shielding and thus the dynamical processes in dense plasmas. Comparisons of our computational predictions and the recent experimental measurements are performed. The current work not only has far-reaching implications for our understanding of the dense plasma screening, but also has potential applications in fusion, laboratory astrophysics, and related disciplines.

Variation of the Photoionization Cross Section Depending on the Choice of Impurities in the Case of GaAs and CdTe

Variation of the Photoionization Cross Section Depending on the Choice of Impurities in the Case of GaAs and CdTe

Spectroscopic Peculiarities at Ionization of Excited 2p5(2PJf)3s[K]0,1,2 States of Ne: Cooper Minima and Autoionizing Resonances

An extensive study of photoionization from neon excited states was performed. The R-matrix approach was applied to calculate a photoionization cross-section from the metastable 2p5(2PJf)3s[K]0,2 and dipole-allowed 2p5(2PJf)3s[K]1 states. The resonance structures and Cooper minimum accessible in photoionization from the excited states by the photons with energy below 30 eV were analyzed. The parameters of the lowest autoionizing states (AISs) of even parity were extracted by fitting of the photoionization cross-section. For the dipole-allowed states, calculations are presented for unpolarized, linearly and circularly polarized radiation.

Angular Distribution of Atomic Photoelectrons as a Function of Photon Field Polarization: Case of Ns-type Light Atoms

The angular distribution of the atomic photoelectrons gives us information on the evolution of the field of the photoelectrons in different directions concerning the incident direction of the electromagnetic radiation which is absorbed by the atom and its direction of polarization. Here, the angular distribution of atomic photoelectrons as a function of photon field polarization was studied theoretically using monocentric wave functions to investigate the influence of polarization on the theoretical results. A GEANT4 modeling calculation based on the Monte Carlo code was made on the helium atom. The calculations were performed at low energy above the atomic ionization threshold. The results obtained by analytical calculation for the total photoionization cross-section were compared with those obtained by a simulation calculation using GEANT4 modeling. A reasonable agreement was observed following this comparison for a range of energy considered in this study.

L -shell photoionization of Mg-like S4+ in ground and metastable states: Experiment and theory

We report measurements of the absolute photoionization cross sections of magnesiumlike ${\mathrm{S}}^{4+}$ over the 158--280 eV photon energy range. The experiments were performed with the multianalysis ion apparatus at the SOLEIL synchrotron radiation facility. Single- and double-ionization ion yields produced by the photoionization of the $2p$ subshell of the ${\mathrm{S}}^{4+}$ both from the $2{p}^{6}3{s}^{2}{\phantom{\rule{0.16em}{0ex}}}^{1}{S}_{0}$ ground state and the $2{p}^{5}3s3p{\phantom{\rule{0.16em}{0ex}}}^{3}{P}_{0,1,2}$ metastable levels were observed, as well as $2s$ excitations. Theoretical calculations of the photoionization cross sections were carried out using multiconfiguration Dirac-Fock and $R$-matrix computer codes and the results are compared with the experimental data. While in general reasonably good agreement was found, notable differences in the strengths and positions of predicted resonances were observed and significant systematic energy shifts of the theoretical predictions were required.

Theoretical Calculations on the Relativistic Corrections and Photoionization Cross Sections for Hydrogenlike Ions in Finite Temperature Dense Plasmas

Theoretical Calculations on the Relativistic Corrections and Photoionization Cross Sections for Hydrogenlike Ions in Finite Temperature Dense Plasmas

Computing photoelectron spectra employing unique continuum functions

Molecular photoelectron spectra are commonly obtained theoretically in Fermi's Golden Rule framework, where the stationary continuum wave function is represented by slowly converging series such as the celebrated partial wave expansion. In this paper, we employ an alternative approach to address the photoionization cross section. While it gives the same cross section as the Golden Rule, this method follows a different route and has a number of advantages. The cross section is computed directly from the probability current density having the (conjugated) Dyson orbital as its source. With this, one arrives at an intuitive interpretation of the photoionization process and avoids employing a long expansion series since the continuum solution is transition-specific and thus unique. We expect this methodology to be particularly beneficial in the case of complexly shaped and delocalized Dyson orbitals.

Total and state-specific electron-ion recombination rates and photoionization of Ca XV for high temperature plasma

The inverse processes of photoionization and electron-ion recombination of (Ca XV + hν↔ Ca XVI + e), are studied using the unified method of Nahar and Pradhan for a large number of bound states, 582 in total with n≤10 and l≤9, for their characteristic features particularly in the high energy region that can impact plasmas at high temperature. The unified method which implements close-coupling (CC) approximation and the R-matrix method includes both the radiative recombination (RR) and dielectronic recombination (DR) for the total recombination and yields self-consistent sets of results for both the inverse processes. The present study, carried out in large scale computations, employs a large CC wavefunction expansion of 29 LS states belonging to n=2,3 complexes of the core ion Ca XVI, and appeared to be the first detailed study for the electron-ion recombination of the ion. The present results include (i) state-specific photoionization cross sections (σPI(nLS)) leaving the core ion in the ground state, (ii) state-specific recombination rate coefficients (αRC(nLS,T)) that include both the RR and DR, (iii) total recombination rate coefficients (αRC) with temperature that include contributions of infinite number of recombined states, and (iv) a spectrum of total electron-ion recombination cross sections and rates with respect to photoelectron energy. The study finds that the core ion excitations from the ground to high n=3 states have introduced Rydberg resonances which are stronger and Seaton resonances which are more enhanced in the high energy region of σPI compared to those introduced by excitations to the n=2 states. Such features have contributed to the shape of the temperature dependent state-specific αRC(nLS,T), and have resulted in three DR bumps/ shoulders in the high temperature region of the total αRC(T) where the third DR bump at temperature of ∼ 4 MK has raised αRC(T) at high T above all previous rates. The results are expected to be accurate within 10%–15% and provide more complete and precise spectral modelings for the high temperature plasmas where the highly charged Ca XV is more abundant.

Study of photoionization cross section and binding energy of shallow donor impurity in multilayered spherical quantum dot

In the framework of the effective mass approximation and by using the finite element method , we have studied the simultaneous effects of position dependent effective mass (PDEM) and dielectric function on the shallow donor impurity binding energy and photoionization cross section in a multilayered spherical quantum dot . We have also investigated the influence of conduction band nonparabolicity and polaronic mass on the both binding energy and photoionization cross section (PCS). The obtained results have shown that the nonparabolicity and polaronic mass effects enhance the binding energy and photoionization cross section. Furthermore, it can be concluded from this research that the binding energy and the PCS are strongly dependent on the geometrical parameters, and PDEM. Changes in binding energy and photoionization cross section have physical reasons, which are discussed in details. • The photoionization cross section (PCS) and the binding energy are strongly dependent on the width of the structure layers. • The conduction band nonparabolicity and the polaronic mass effects enhance the binding energy and reduce the PCS peak magnitude. • The dependence of the dielectric function ε ( r ) on the electron coordinates makes the amplitude peak of the PCS take high values.

Intense terahertz laser field induced electro-magneto-donor impurity associated photoionization cross-section in Gaussian quantum wires

Using expressions derived within the compact density matrix approach, the peaks of optical absorption and the changes of refractive index of a hydrogenic impurity in a GaAs/GaAlAs Gaussian quantum well wire are calculated taking into account the influence of static electric, magnetic and intense laser fields. The photoionization cross section, with normalized photon energy, is computed for different values of static electric field, magnetic field, and laser dressing parameter. The dipole moment matrix elements and the transition energy between ground and first excited state energy levels are computed as functions of quantum wire width and confinement potential depth, with and without external perturbations. Donor impurity binding energy is investigated in presence of the aforementioned electromagnetic probes, using parabolic band and effective mass approximations. The results show that the absorption coefficients depend on the transition energy difference between initial and final states involved as well as on the corresponding polarization response via dipole matrix elements. Discussed optical properties are field-sensitive and they can be tuned within the desired energy ranges using these external perturbations. • Peaks of optical absorption and changes of refractive index of a hydrogenic impurity in a GaAs/GaAlAs Gaussian quantum well wire are calculated. • They have been computed taking into account the influence of static electric, magnetic and intense laser fields. • Photoionization cross section, with normalized photon energy, is computed. • Donor impurity binding energy is investigated in the presence of aforementioned electromagnetic-probes, using parabolic band and effective mass approximations. • Discussed optical properties are field-sensitive and they can be tuned within the desired energy ranges using these external perturbations.

Atomic radiative data for oxygen and nitrogen for solar photospheric studies

Aims. Our recent reanalysis of the solar photospheric spectra with non-local thermodynamic equilibrium (non-LTE) models resulted in higher metal abundances compared to previous works. When applying the new chemical abundances to standard solar model calculations, the new composition resolves the long-standing discrepancies with independent constraints on the solar structure from helioseismology. Methods. Critical to the determination of chemical abundances is the accuracy of the atomic data, especially the f values, used in the radiative transfer models. Here we describe, in detail, the calculations of f values for neutral oxygen and nitrogen used in our non-LTE models. Results. Our calculations of f values are based on a multi-method, multi-code approach and they are the most detailed and extensive of its kind for the spectral lines of interest. We also report in this paper the details of an extensive R-matrix calculation of photoionization cross sections for oxygen. Conclusions. Our calculation resulted in reliable f values with well-constrained uncertainties. We compare our results with previous theoretical and experimental determinations of atomic data. We also quantify the influence of adopted photoionization cross sections on the spectroscopic estimate of the solar O abundance, using data from different sources. We confirm that our 3D non-LTE value is robust and unaffected by the choice of photoionization data, contrary to the recent claim made by Nahar.

Theoretical study of the enhancement of saturable absorption of Kr under x-ray free-electron laser

The generation of hollow atoms will reduce the probability of light absorption and provide a high-quality diffraction image in the experiment. In this paper, we calculated the ionization rate of the Kr atom under x-ray free-electron laser (XFEL) using Hartree–Fock–Slater model and simulated the ionization model of Kr atom using Monte–Carlo method to determine the response of the hollow atom of Kr atom to the XFEL photon energy. Calculating the correlation between the total photoionization cross-section of the ground state of Kr atom and the photon energy, we determined three particular photon energies of 1.75 keV, 1.90 keV, and 14.30 keV. The dynamics simulation under the experimental condition’s 17.50 keV photon energy was achieved by implementing the Monte–Carlo method and calibrating the photon flux modeling parameters. Consequently, our calculated data are more consistent with experimental phenomena than previous theoretical studies. The saturable absorption of Kr at 1.75 keV, 1.90 keV, 14.30 keV, and 17.50 keV energies was further investigated by using the optimized photon flux model theory. We compared the statistics on main ionization paths under those four specific photon energies and calculated the population changes of various Kr hollow atoms with different configurations. The results demonstrate that the population of hollow atoms produced at the critical ionization photon energy is high. Furthermore, the change of population with respect to position is smooth, which shows a significant difference between the generation mode of ions with low and high photon energies. The result is important for the study of medium- and high-Z element hollow atoms, which has substantial implications for the study of hollow atoms with medium and high charge states, as well as for the scaling of photon energy of free electron lasers.

TL and OSL characteristics of the fluoroperovskite KMgF3:Eu,Yb, Li for dosimetry applications

The purpose of this work was to investigate the dosimetric and luminescence properties of the novel KMgF3:Eu0.5%,Yb0.1%,Li15% fluoroperovskite synthesized using the sol-gel method. The luminescence signals were characterized using Optically Stimulated Luminescence (OSL) spectra, Linearly-Modulated OSL (LM-OSL), Continuous-Wave OSL (CW-OSL), and Thermoluminescence (TL) techniques. The blue light (470 nm) stimulated OSL associated with Eu2+, and Eu3+ emissions was correlated with the TL peaks up to 300 °C. The photoionization cross-section of each OSL component was evaluated using deconvolution analysis following two different optical stimulation modes, namely LM-OSL and CW-OSL. The activation energy values were evaluated using the Tm-Tstop and CGCD methods. OSL signal fading of 5% and 13% was observed at the end of 24 h and over the next three months, respectively. The results indicate that the OSL from KMgF3:Eu0.5%,Yb0.1%,Li15% fluoroperovskite has suitable properties for dosimetry, including high sensitivity to ionizing radiation and a wide linear dose range (0.1–500 Gy). These results enhance the understanding of the origin of the luminescence properties in this material and this work paves the way toward its utility for dosimetry purposes.

Contribution of near-edge processes to the L X-ray emission lines for various lanthanum (III) compounds

The present measurement illustrates the study of near-edge processes and the intensity ratios [ILl/ILα, ILβ1/ILα and ILl/ILβ1] for Mn Kα1,2 X-rays across the L2 edge of lanthanum in its various chemical forms viz., lanthanum oxide (La2O3), lanthanum oxalate (C6La2O12) and lanthanum acetate (C6H9LaO6) at four different scattering angles i.e. 90°, 105°, 115° and 125° with a lab-scale X-ray fluorescence (XRF) spectrometer. The current observation reveals that the Lβ1 X-ray emission lines exhibit a variance of ∼ (21–40) % between measured and calculated fluorescence cross-sections. Apart from this, the measured values of intensity ratios have been compared with the three data sets of calculated values using L shell emission rates based on the Dirac-Fock (DF) model, total X-ray emission rates and photoionization cross-section values based on the relativistic Hartree-Slater (RHS) model and three sets of Coster-Kronig (CK) and fluorescence yields. The correlation between crystal structure, bond distance and intensity ratio are also discussed in this work.

Combined effects of hydrostatic pressure and electric field on the donor binding energy, polarizability, and photoionization cross-section in double GaAs/Ga$$_{1-x}$$Al$$_{x}$$As quantum dots

Combined effects of hydrostatic pressure and electric field on the donor binding energy, polarizability, and photoionization cross-section in double GaAs/Ga$$_{1-x}$$Al$$_{x}$$As quantum dots

Photoionization cross section of first excited state of lithium

We report the accurate quantitative measurements of the photoionization (PI) cross section of lithium-7 confined in a magneto-optical trap (MOT). The losses from the MOT induced by radiation of the low-power light-emitting diodes (LEDs) are measured as a function of the photoionizing radiation intensity. On the basis of these measurements, the PI cross section from the 2P3/2 excited state of lithium is evaluated for three different LEDs. The PI cross sections of lithium from the 2P3/2 state at 259, 280, 307 nm are determined to be (5.4 ± 0.4), (8.1 ± 0.8) and (9.5 ± 1.1) Mb respectively. Accuracy of our measurements is better than that of previous reported results. The semiclassical calculations taking into account the fine structure of the first excited state of lithium are performed. Our values are in good agreement with experimental results earlier reported and are consistent with the theoretical data.

Novel Sm3+ doped BaZn2(PO4)2 glass-ceramic for optically stimulated luminescence dosimetry

Sm3+ doped glass-ceramic with crystallized BaZn2(PO4)2 was prepared and its structural, optical, and stimulated luminescence dosimetry properties were investigated. The excitation and emission spectra of photoluminescence exhibit Sm3+ associated transitions. The relationship between the doping concentration and the optically stimulated luminescence (OSL) intensity was investigated. The OSL intensity reached a maximum at a Sm3+ concentration of 0.25 mol%, after that, a concentration quenching was observed. The OSL decay curves of BaZn2(PO4)2: 0.25Sm3+ glass-ceramic are deconvoluted by using general order kinetics show the two components that contribute to the OSL signal with photoionization cross sections of 1.693 × 10−17 and 2.443 × 10−18 cm2, respectively. The thermoluminescence curve has two peaks at 393 and 477 K. The linear radiation dose response range is identified as 0.2-500 Gy. These results show that Sm3+ doped BaZn2(PO4)2 glass-ceramic has the potential to be used as a candidate material for radiation dosimetry.

Non-LTE abundances of zinc in different spectral type stars and the Galactic [Zn/Fe] trend based on quantum-mechanical data on inelastic processes in zinc-hydrogen collisions

ABSTRACT We present a new model atom of Zn i-Zn ii based on the most up-to-date photoionization cross-sections, electron-impact excitation rates, and rate coefficients for the Zn i + H i and Zn ii + H− collisions. The latter were calculated using the multichannel quantum asymptotic treatment based on the Born–Oppenheimer approach. Non-LTE analysis was performed for the first time for lines of Zn i and Zn ii in the ultraviolet (UV) spectra of two very metal-poor reference stars: HD 84937 and HD 140283. We found consistent non-LTE abundance from the resonance Zn i 2138 Å line, the subordinate lines, and the lines of Zn ii. In both stars, non-LTE leads to 0.17 dex higher average abundance from Zn i, while, for Zn ii lines, non-LTE corrections are minor and do not exceed 0.06 dex. Using lines of Zn i in the high-resolution spectra, we determined the non-LTE abundances for a sample of 80 stars in the −2.5 ≤ [Fe/H] ≤ 0.2 metallicity range. The [Zn/Fe] versus [Fe/H] diagram reveals a dip, with [Zn/Fe] ≃ 0.3 in the most metal-poor stars, a close-to-solar value for [Fe/H] ∼−1.2, and increasing [Zn/Fe] up to 0.3 in the thick disc stars. The close-to-solar metallicity stars have subsolar [Zn/H] ≃ −0.1, on average. Non-LTE abundances of zinc were derived for the first time for seven reference F- to B-type stars. We provide a grid of the non-LTE abundance corrections.

Photoionization of helium atom embedded in classical non-ideal plasma at high non-relativistic photon energies

The effects of the non-ideality (NI) of classical plasmas on the photoionization of helium atoms at high non-relativistic photon energies are investigated within the framework of the dipole approximation. Screened interaction in non-ideal plasmas is represented by an effective potential, deduced from a solution of Bogolyubov's hierarchy equations on discarding the effects of quantum degeneracy. A highly correlated wave function consisting of 715 terms for the ground state of helium has been used to evaluate the dipole matrix element. Changes in the asymptotic cross sections of single, double, and total photoionizations due to varying NI of plasmas have been investigated in detail. Particular emphasis is made to study the changes in the asymptotic ratio of the double-to-single photoionization cross section caused by the variation of non-ideality parameter in a wide range. It is found that increasing plasma NI makes the feasibility of occurrence of double photoionization to broaden.

Determination of the intensity/energy response function of a hemispherical photoelectron analyser based on Tougaard background

A new method is proposed for the determination of the intensity/energy response function of a hemispherical electrostatic analyser as commonly used in photoemission spectroscopy. It only requires the measurement of a wide spectrum of a reference metallic sample. Based only on the knowledge of the Tougaard inelastic electron scattering cross section and an educated parametrization of the response function, the retrieval algorithm minimizes the area of the background subtracted primary spectrum with some constraints. Sound results for different metals (Ag, Au, Cu, Zn) are obtained (i) on two different photoemission instruments (ii) in both fixed analyser transmission and fixed retarding ratio modes (iii) for various lens and slits settings (iv) for both monochromated and unmonochromated x-ray sources. The linear correlation between core level areas and the product of tabulated inelastic mean free paths and of photo-ionization cross sections validates the approach.