Multiple Ionization Effects Research Articles

Au L-shell x-ray emission induced by 154.3–423.9 MeV/u C6+ ions

The L-shell x-ray emissions of gold are investigated for the bombardment of high energy C6+ ions in the high energy region of 154.3–423.9 MeV/u. Due to the multiple ionization of outer-shell electrons at the movement of L x-ray emission, the blue shift of the experimental x-ray energy and an enhancement of the relative intensity ratios of Lι, Lβ–Lα x rays are observed. Using the improved thin target formula and considering the effect of multiple ionization on atomic parameters, the L-subshell x-ray production cross sections are extracted from the counts and compared with the theoretical estimations of BEA, PWBA and ECPSSR. It is found that the relative corrections of ECPSSR on PWBA can be ignored in the present experimental energy region. The calculations of PWBA and ECPSSR are almost identical and both are larger than the experimental results. The BEA is in better agreement with the experiment as a whole.

Multiple ionization of iodine for 2.5\u20135.0 MeV I22+ ions impacting on Fe target

The L-shell X-ray emissions of iodine are investigated as a function of the incident energy for I22+ ions impacting on Fe target in the energy region near the Bohr velocity. Six distinct L-subshell X-rays, Lι, Lα1, 2, Lβ1, 3, 4, Lβ2, 15, Lγ1 and Lγ2, 3, 4, 4', are observed. Compared to the atomic data, the energy of the experimental X ray shifts to the higher energy side. The relative intensity ratios of Lι, Lβ1, 3, 4, Lβ2, 15, to Lα1, 2, Lι to Lβ2, 15 and Lγ2, 3, 4, 4/ to Lγ1 are enhanced, but has no obvious change with the increase of projectile energy in the present energy region. That is interpreted by the multiple ionization effect of the M-, N- and O-shell electrons.

Understanding the mechanisms of L-shell x-ray emission from Os atoms bombarded by 4–6 MeV/u fluorine ion

The L-subshell ionization mechanism is studied in an ultra-thin Os target bombarded by 4–6 MeV/u fluorine ions. Multiple ionization effects are considered through the change of fluorescence and Coster-Kronig yields while determining L-subshell ionization cross sections from L x-ray production cross sections. The present experimental values are compared with various theoretical approximations: (i) the relativistic semi-classical approximation (RSCA), (ii) the shellwise local plasma approximation (SLPA), and (iii) the ECUSAR theory. We also take into account the vacancy sharing among the subshells by the coupled-states model (CSM) and the electron capture (EC) by a standard formalism. We find that the ECUSAR-CSM-EC describes the measured excitation function curves the best. However, the theoretical calculations are still about a factor of two smaller than the measured values even though the recent fluorescence and Coster-Kronig yields are considered. Hence, a re-evaluation of these parameters is a challenge for the theoretical works. Whatsoever, this work leads to demonstrate that in the present energy range the heavy-ion induced inner-shell ionization of the heavy atoms can be understood by combining the direct Coulomb ionization, the electron capture, and the vacancy sharing among subshells, together with optimizing the atomic parameters. Optimization of the atomic parameters shows that our experimental results agree with theoretical vacancy production theories if the L1 fluorescence yield is nearly doubled. Such a optimization is validated by the proton induced L-shell ionization data of uranium atoms.

K-shell ionization cross sections of Cu, Zn and Ge by 3–5 MeV/u Si-ion bombardment

The K x-ray spectra of different targets (Cu, Zn, and Ge) induced by 3 to 5 MeV/u Si projectile ions have been measured to determine the K-shell ionization cross-section. A significant difference is observed between the measurements and theoretical estimates, where the theoretical ones are about 28–35% of the experimental results. Such difference is reduced to a good extent 51%–56% if multiple ionization effects are taken into account. Remaining discrepancy may be attributed to the electron capture contribution.

Measurement of L-shell X-ray production cross sections in 89Y, 158Gd and 209Bi due to 0.3 MeV/u – 1.0 MeV/u 12C ions

Experimental heavy ion induced X–ray production cross sections in matter continue to be of importance for both fundamental ion-atom collision studies as well as practical applications such as in nuclear analytical techniques. This work presents results of L-shell X-ray production cross section measurements in 89Y, 158Gd and 209Bi due to 4 MeV–12 MeV 12Cq + projectile ions. Experimental data are compared with theoretical calculations based on the ECPSSR, ECPSSR + EC and ECPSSR-UA models. Data show fairly good, albeit energy dependent agreement with the different models for yttrium and gadolinium cross sections. For bismuth, all three models overestimate data by an almost constant factor of two. The effect of multiple ionization on the l-line intensity ratios is also presented for gadolinium and bismuth targets.

Yield of the Fricke dosimeter irradiated with the recoil α and Li ions of the 10B(n,α)7Li nuclear reaction: effects of multiple ionization and temperature

Monte Carlo track chemistry simulations were used to investigate the effects of multiple ionization (MI) of water on the yields (G values) of the ferrous sulfate (Fricke) dosimeter, which was irradiated with low-energy α and lithium ion recoils from the 10B(n,α)7Li nuclear reaction as a function of temperature from 25 to 350 °C. Calculations were performed individually for 1.47 MeV α-particles and 0.84 MeV lithium nuclei with dose-average linear energy transfer (LET) values of ∼196 and 225 keV/µm at 25 °C, respectively. The total yields were obtained by summing the G values for each recoil α and Li ion weighted with its fraction of the total energy absorbed. At room temperature, our G(Fe3+) values calculated under aerated and deaerated conditions only agreed well with the experimental results, provided the MI of water was incorporated in the simulations. This strongly supports the importance of the role of MI of water in the high-LET radiolysis of water. We also simulated the effects of MI of water on G-values for the primary species of the radiolysis of deaerated 0.4 M H2SO4 aqueous solutions by 10B(n,α)7Li recoils. As with the Fricke dosimeter, the best agreement between experiment and simulation was found at 25 °C when the MI of water was included in the simulations. It was also shown that G(Fe3+) decreases slightly as a function of temperature over the range of 25–350 °C. However, at elevated temperatures, no experimental data were available with which to compare our results.

L-shell x ray production cross sections of Sm and Yb induced by carbon ions between 2 MeV and 5 MeV

We have measured L-shell x rays for Sm and Yb induced by carbon ions with energies between 2 and 5 MeV. The measured spectra have been used to extract the individual Li (Lα, Lβ, Lγ and Lℓ) and total L-shell x ray production cross sections. Related ionizations cross sections for Li sub-shells have been determined from individual measured L-shell x ray production cross sections, L-shell fluorescence and Coster-Kronig yields corrected by the multiple ionization effects. The results have been compared with the available experimental data from the literature as well as with the predictions of the PWBA and ECUSAR theories. The analysis of data shows that the ECUSAR predictions agree well with our experimental data.

Experimental and theoretical L-shell ionization cross sections of heavy atoms by impact of Si ions

We present a theoretical and experimental study of the subshell resolved L-shell ionization of relativistic targets such as 73Ta, 78Pt, 90Th, and 92U. The measurements of x-ray production cross sections by (84–140 MeV) Si+q ions (q = 8; 12), were held at the Inter-University Accelerator Centre of New Delhi. Multiple-hole fluorescence and Coster-Kronig yields were used to obtain the Li(i = 1–3) ionization cross sections from the measured x-ray production cross sections of Lℓ, Lα, and Lβ, Lη, and Lγ lines. The experimental results are compared with ab initio theoretical calculations by means of the shell-wise local plasma approximation (SLPA). This model uses the quantum dielectric formalism to obtain the total ionization cross sections from an initial ground state. The wave functions and binding energies of the different targets were obtained by solving the fully relativistic Dirac equation using the HULLAC code package. These calculations are based on first order perturbation theory with a central field, including Breit interaction and quantum electrodynamics corrections. The present SLPA ionization cross sections of the L-shell are found to be independent of the charge state of the Si ions. The experimental observations display also quite similar character if the correct mean projectile charge state inside the target is used for including the multiple ionization effect during ion-solid collisions. A general good agreement between the experimental measurements and full theoretical calculations supports the reliability of present results. The comparison also includes the well-known ECPSSR and ECUSAR semi empirical approximations. We noted that the ECUSAR results agree well with the SLPA, while the ECPSSR cross sections are rather low.

Multiple ionization effect in Dy, Ho and Er at low proton energy

SynopsisThe L shell X-ray production cross sections for elements (Z = 66, 67 and 68) at three different low proton energies i.e. 260, 280 and 300 keV have been investigated. Calculations are based on the ECPSSR model and its modified form i.e. ECPSSR-UA model. During calculations with ECPSSR theory, a significant phenomenon known as multiple ionization (MI) has been included. Theoretically calculated values are compared with the experimental values. The calculations with ECPSSR-MI shows improved results.

Evaluation of multiple ionization effect in collision of low energy proton with Au, Pb, and Bi

A careful evaluation of atomic parameters such as fluorescence yields and Coster-Kronig probabilities provides a platform to interpret the atomic properties of matter in an appropriate way. Investigations are made for these parameters of Gold (79Au), Lead (82Pb), and Bismuth (83Bi) bombarded by the protons in the low energy regime i.e. 260–400 keV. An important phenomenon i.e. Multiple Ionization (MI) effect, which enormously influenced them is included in the present calculations. The calculated results are compared with the experimental measurements. It is analyzed that the predictions involving MI effect agree well with the experimentally measured values as compared to the calculations without it.

Multiple ionization effect of Au induced by different ions

We report the experimental data of characteristic X-ray spectra produced by the impact of H<sup>+</sup>, Ar<sup>8+</sup>, Ar<sup>12+</sup>, Kr<sup>13+</sup> and Eu<sup>20+</sup> ions with different kinetic energies on Au surface in the National Laboratory of Heavy Ion Research Facility in Lanzhou, China. The energy shifts of X-ray spectra are analyzed and the ratio of X-ray yield is calculated. The results show that H<sup>+</sup> can excite the characteristic X-ray spectra of M<sub>ζ</sub> and M<sub>α</sub> of Au, while Ar<sup>8+</sup>, Ar<sup>12+</sup>, Kr<sup>13+</sup> and Eu<sup>20+</sup> can excite the characteristic X-ray spectra of M<sub>ζ</sub>, M<sub>α</sub>, M<sub>γ</sub> and M<sub>δ</sub> of Au, because the inner shells of target atom are multiply ionized by heavy ions impact, so that the relative intensity ratio of the X-rays changes when the heavy ions are incident. There are different energy shifts of Au M X-ray due to multiple ionization effect in collision. When the ion incident energy is lower, the degree of multiple ionization of the inner shells of the target atom is almost independent of the incident energy, when the ion energy is higher, the degree of multiple ionization increases with incident ion energy increasing. At the same time, the degree of multiple ionization also depends on the number of holes in the outer shell of the ion and its atomic number. That the ratio of X-ray yield increases with the increase of the atomic number of the incident ion further indicates that the degree of multiple ionization increases with atomic number of the incident ion increasing. The multiple ionization and electron configuration of the inner shells of the atom can be determined by the energy shift and spectra broadening. These measurements provide basic data for further studying the multiple ionization mechanism of the inner shells of the atom. But due to the limitation of the resolution of the detector, the spectral broadening data cannot be measured. It is necessary to use a higher-resolution detector to further study the multi-ionization effect of the inner shells of the atom.

Multiple ionization effects on L X-ray emission in Bi by proton impact

SynopsisL X-ray intensity ratios for Bismuth (Bi) as a function of proton energy has been calculated in the energy range 260 – 400 keV. An important phenomenon i.e. Multiple Ionization (MI) effect, which influenced the X-ray production process included in the calculations. These are based on the ECPSSR model using the data basis of different workers. Theoretically calculated values are compared with the experimental measurements and show fairly a well agreement over the entire energy region except at lower energy edge. The present results clearly illustrate the significance of multiple ionization effect and offer relatively good opportunity to bring the theoretical values closer to the experimental measurements.

Multiple ionization of Au by fast Sq+ ions of energy 0.4–3.8 MeV/amu

The measurements of the M- and N-shell ionization probabilities in gold bombarded by highly charged Sq+ (q=4–14) ions of energy 0.4–3.8MeV/amu are reported. The ionization probabilities were extracted from the measured L-X-ray spectra which were substantially modified by the multiple ionization effects. The observed L-X-ray line shifts and broadening allowed us (Banaś et al., 2002) to extract both the M- and N-shell ionization probabilities for the zero impact parameter. These ionization probabilities, which correspond to the moment of X-ray emission, were correlated with the ionization probabilities for the moment of ion impact ionization by using the vacancy rearrangement procedure developed here. In this way the ionization probabilities for the moment of ion impact multiple ionization were obtained. By comparing to the theoretical predictions of the semiclassical approximation (SCA) (Trautmann and Kauer, 1989) and the “geometrical model” (GM) (Sulik et al., 1987) based on the binary encounter approximation (BEA), the role of the electronic wave functions and the binding effect is discussed. Generally, the calculations using the hydrogenic wave functions reproduce the measured ionization probabilities.

Effects of multiple ionization in atomic gases irradiated by one- and two-color ultrashort pulses

The dynamics of femtosecond light pulses ionizing noble gases from single or multiple ionization schemes are numerically compared, with the emphasis on two-color pulses. We discuss the influence of multiply-charged ions on the excitation of harmonics in focused propagation and on the supercontinuum and clamping intensity of laser filaments. Depending on the atom’s first binding energy, multiple ionization based on Ammosov–Delone–Krainov (ADK) tunneling rates can increase the peak intensities, the number of harmonics or the spectral blueshifts, compared with quasistatic hydrogen-like rates. With two-color pulses, noticeable differences occur in the frequency domain corresponding to broadband terahertz pulses.

Ionization of highly charged iodine ions near the Bohr velocity

We have measured the L-shell X-rays of iodine from the collisions of 3MeV Iq+(q=15,20,22,25,26) ions with an iron target. It is found that the X-ray yield decreases with the increasing initial charge state. The energy of the subshell X-ray has a blue shift, which is independent of the projectile charge state. In addition, the relative intensity ratios of Lβ1,3,4 and Lβ2,15 to Lα1,2 X-ray are obtained and compared with the theoretical calculations. That they are larger than for a singly ionized atom can be understood by the multiple ionization effect of the outer-shell electrons.

Ionization of Ar11+ ions during collisions near the Bohr velocity

The K-shell X-rays of argon from the collisions of 1–3MeV Ar11+ ions with V target were measured. It was found that the Kα X-ray shifts to the high energy by 52eV, and the intensity ratio of Kβ/Kα was larger than the atomic data, owing to the presence of 2p multiple vacancies. The X-ray production cross sections were obtained and compared with BEA, PWBA and ECPSSR theoretical predictions. The BEA model, taking into account the ionic binding energy, coulomb repulsion and multiple ionization effect on fluorescence yield, presented a better agreement with the experimental cross section data.

Effects of multiple ionization on total L X-ray emission by proton impact

The effects of multiple ionization on L X-ray emission by proton with energy from 100 keV to 250 keV on iron target was studied. The total L X-ray production cross sections were measured. A multiple ioniza-tion model and an average fluorescence yield were used together. The theoretical predictions with the correction of atomic parameter were obtained.

Measurement of L X-ray production cross sections by impact of proton beams on Hf, Ir, and Tl

In spite of the existence of a large quantity of experimental results for X-ray production cross sections by proton beam impact, recent publications emphasize the need for more measurements in several targets and energy ranges. Following these recommendations, this work presents results with some heavy elements (72Hf, 77Ir, and 81Tl) irradiated with protons in the energy interval 0.45 MeV–4.75MeV. The results are compared with experimental data from previous publications, empirical tables, as well as with predictions of the ECPSSR theory with the United Atom modification, intra-shell coupling corrections, and Multiple Ionization effects. Although there is good coincidence with previous experiments, the agreement among the theories with the experimental data does not allow a definitive conclusion about the best predictions for the measured cross sections.

Al K-shell x-ray production cross section induced by proton and highly charged heavy ions

Al K-shell x-ray production cross sections induced by 50–250 keV protons and 1–3 MeV Ar11+ ions were measured. It was found that 3–4 L-shell electrons of the Al atom were multiply ionized by Ar11+ ion impact. The x-ray production cross sections were deduced from the experimental yield data and compared with binary encounter approximation (BEA), plane wave Born approximation and energy-loss Coulomb-repulsion perturbed-stationary-state relativistic (ECPSSR) theoretical predictions. For proton impact, the ECPSSR theory gave an accurate prediction of the experimental result. However, taking into account the multiple-ionization effect on fluorescence yield, the BEA model presented better agreement with the cross section data produced by Ar11+ ions.

Multiple ionization effects in M X-ray emission induced by heavy ions

M-shell ionization of tungsten by Ar12+ ions were investigated in the energy range of 1.2–3.0 MeV. The measurements were also implemented for H, He and Xe ions as a comparative study. A significant shift of the M X-ray lines to the higher energy side caused by multiple ionizations, which was verified by the analysis of the intensity ratios of Mγ and Mαβ, was observed. The total experimental cross sections of tungsten were compared with the PWBA and ECPSSR theoretical predictions, which are based on two extreme assumptions, namely, single ionization and full ionization.