Shell Vacancy Production Research Articles

Single and double K -shell vacancy production in slow Xe54+,53+ -Xe collisions

We present an experimental and theoretical study of symmetric $\textrm{Xe}^{54+}+\textrm{Xe}$ collisions at 50, 30, and 15 MeV/u, corresponding to strong perturbations with $v_K/v_\text{p}$ = 1.20, 1.55, and 2.20, respectively ($v_K$: classical $K$-shell orbital velocity, $v_\text{p}$: projectile velocity), as well as $\textrm{Xe}^{53+}+\textrm{Xe}$ collisions at 15 MeV/u. For each of these systems, x-ray spectra were measured under a forward angle of $35^\circ$ with respect to the projectile beam. Target satellite and hypersatellite radiation, $K\alpha_{2,1}^\mathrm{s}$ and $K\alpha_{2,1}^\mathrm{hs}$, respectively, were analyzed and used to derive cross section ratios for double-to-single target $K$-shell vacancy production. We compare our experimental results to relativistic time-dependent two-center calculations.

M-shell ionization of heavy elements by0.1–1.0MeV∕amuH1,2andHe3,4ions

The $M$-shell ionization in high-$Z$ atoms by low-energy light $_{1}^{1}\mathrm{H}$, $_{1}^{2}\mathrm{H}$, $_{2}^{3}\mathrm{He}$, and $_{2}^{4}\mathrm{He}$ ions have been studied systematically in the energy range $0.1--1.0\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\mathrm{amu}$ in order to verify the available theoretical approaches describing the $M$-shell ionization by charged particles in asymmetric collisions. The present low-energy data, combined with our earlier results reported for $M$-shell ionization by hydrogen and helium ions for higher energies, form a systematic experimental basis to test the theoretical predictions of $M$-shell ionization based on the plane-wave Born approximation (PWBA), the semiclassical approximation (SCA), and the binary-encounter approximation (BEA). In the PWBA based approaches the energy loss (E), Coulomb deflection (C), perturbed stationary state (PSS), and relativistic (R) effects were considered within the ECPSSR theory and its recent modification, called the ECUSAR theory, in which a description of the PSS effect was corrected to account for the united- and separated-atom (USA) electron binding energy limits. In the SCA calculations with relativistic wave functions the binding effect was included only in the limiting cases of separated-atom and united-atom limits. Possible contribution of the electron capture, multiple ionization, and recoil ionization to the $M$-shell vacancy production, which is dominated for light ions impact by direct single ionization process, are also discussed. The universal scaling of measured $M$-shell x-ray production and ionization cross sections was investigated in detail. Using the present data the isotopic effect has been studied by comparing the measured $M$-shell ionization cross-section ratios for equal-velocity hydrogen $_{1}^{1}\mathrm{H}$ and $_{1}^{2}\mathrm{H}$ as well as helium $_{2}^{3}\mathrm{He}$ and $_{2}^{4}\mathrm{He}$ isotopes. In addition, the ratios of measured ionization cross sections for $_{1}^{2}\mathrm{H}$ and $_{2}^{4}\mathrm{He}$ were used to investigate the role of the binding effect. The present results are of practical importance for the application of particle-induced x-ray emission technique in trace element studies.

Dynamics of formation ofK-hole fractions of sulfur projectiles inside a carbon foil

The $K\ensuremath{\alpha}$ and $K\ensuremath{\beta}$ satellite and hypersatellite x-ray lines emitted by highly ionized sulfur projectiles passing with energies from $65\phantom{\rule{0.3em}{0ex}}\text{MeV}$ up to $122\phantom{\rule{0.3em}{0ex}}\text{MeV}$ through carbon foils of thickness of $15\text{\ensuremath{-}}210\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}{\mathrm{g}\phantom{\rule{0.3em}{0ex}}\text{cm}}^{\ensuremath{-}2}$ have been recorded using a Si(Li) detector. The additional hypersatellite $K{y}^{h}$ peak proves that for such high energies of the sulfur ions very high subshells ($4p$ and $5p$) could be occupied. In order to study the dynamics of formation of $K$-shell vacancy fractions of sulfur projectiles passing through a carbon foil the dependence of sulfur $K$ x-ray production cross sections on foil thickness has been examined separately for each recorded line using the three component model. For each projectile energy the values of $K$-shell hole production cross sections and $K$-shell electron capture cross sections (both common for all recorded x-ray lines in the case of each projectile energy) have been fitted, as well as the specific values (for each recorded x-ray line) of $K$-shell hole filling cross sections, which are directly connected with average lifetimes of appropriate states of sulfur ions. The obtained ``experimental'' values of $K$-shell vacancy production cross sections are much higher than the theoretical predictions. This suggests that apart from the ionization process the excitation from $K$ shell into higher shells is responsible for a production of $K$-shell vacancies, which has been confirmed by recent classical trajectory Monte Carlo calculations.

Ejectedelectron-ion coincidence measurements of multiple ionization ofargon by 10-24 keV electron impact

The charge state spectra of argon ions produced in singlecollisions by electrons having energies from 10 to 24 keVwith argon atoms have been measured by using the ejectedelectron-ion coincidence technique. Charge analysis of theions is accomplished by a time-of-flight mass spectrometer equipped with a channeltron while the ejected electrons aredetected by another channeltron, both being used in thepulse-counting mode. The ions and the electrons are detected at90° to the incident electron beam direction. Therelative abundance of argon ions in charge state n up to n = 4 + was deduced from the experiment. The charge state fractionsFn of ions with charge states n are found to be constantin the investigated impact energy range. However, their valuesare seen to decrease rapidly with n. A good agreement isobtained between our experimental results and the calculationsbased on inner shell ionization cross sections folded with charge state abundances, which result from the decay of thecorresponding initial inner shell vacancies. This agreementsupports the idea that the multiple ionization of argon atomsby energetic electrons is caused mainly due to inner shellvacancy production followed by relaxation processes resultingin an increase of the charge state of the generated ion. Further,our results show that the Ar+ ions are produced mainlythrough dipole transitions while ions having n>1 + aredominantly produced by the non-dipole transitions in the entireenergy range of investigation. The partial ionizationcross sections for Arn + ions (n = 1-4) are found tobe in close agreement with the results of other workers in the overlapping region of impact energies.

Production of Hollow Lithium by Multielectron Correlation in95MeV/nucleonAr18++LiCollisions

Double-K -shell-vacancy production in Li by 95 MeV/nucleon Ar{sup 18+} projectiles was investigated using high-resolution electron spectroscopy. The two K vacancies are found to come about mainly by ionization and excitation, giving rise to excited states in hollow Li{sup +} . Strong line intensities from the 2s{sup 2}thinsp{sup 1}S and 2s3sthinsp{sup 3}S configurations provide spectral identification for the electron-electron interaction. Production of the 2s3sthinsp{sup 3}S state, with an intensity greater than that for 2s{sup 2}thinsp{sup 1}S , is attributed to a three-electron transition involving correlation. {copyright} {ital 1999} {ital The American Physical Society }

Copper L X-ray spectra measured by a high resolution ion-induced X-ray spectrometer

High resolution L X-ray emission spectra of Cu have been measured by 0.75 MeV/u H, He, and F, 0.73 MeV/u Ar, 0.64 MeV/u Si, and 0.073 MeV/u Si ion impacts with a crystal spectrometer. The X-ray transition energies in the Cu target for Lι, Lη, L α 1,2, L β 1, and L β 3,4 diagram lines induced by H ion impact are determined, which are in good agreement with those given in the reference by Bearden ( Rev. Mod. Phys. 39, 78, 1967). The X-ray spectra produced by F, Si, and Ar ions have complicated structures due to multiple L and M shell vacancy production. The L α 1,2 and L β 1 emission spectra for H and He ions are compared with the calculated ones based on the multiconfiguration Dirac-Fock method. The origin of the broadening of the L α 1,2 line to the lower energy for H ion impact is attributed to one 2p plus one 3d electron vacancy production.

HEAVY ION-INDUCED COPPER L X-RAY SPECTRA MEASURED WITH A HIGH RESOLUTION X-RAY CRYSTAL SPECTROMETER

High resolution L X-ray emission spectra of Cu have been measured for 0.75 MeV/u H , 0.075 and 0.75 MeV/u F , and 0.075 and 0.64 MeV/u Si ion impacts with a Bragg crystal spectrometer. The high resolution X-ray spectra from the Cu thick target for L ι, L η, L α1,2, L β1, and L β3,4 transitions induced by ion excitation are obtained. The X-ray spectra produced by F and Si ion impacts have complicated structures due to multiple L and M shell vacancy production. The L X-ray emission spectra produced by heavy ion impact are compared with the calculated ones based on the Hartree-Fock-Slater method. The origin of the broadening of the L X-ray transition lines to the higher energy side for heavy ion impact is attributed to one 2p plus multiple 3p and 3d electron vacancy production.

Calculation of inner shell excitation in the collision system Ni--Pb

Using an R-dependent atomic basis for static molecular calculations we get accurate single particle energies and dynamic coupling matrix elements. We present our ab initio calculations of inner shell vacancy production for the scattering systems Ni11+-Pb at 1.5 MeV/N and Pb42+-Ni at 1.4 MeV/N.

K-K-electron transfer and K-shell-vacancy production cross sections for Ti bombarded by 28Si and 32S beams at 1.25-4.70 MeV/amu.

Single and double [ital K]-[ital K]-electron transfer and the [ital K]-shell-vacancy production cross sections for Ti bombarded by [sup 28]Si and [sup 32]S beams at energies varying between 1.25 and 4.7 MeV/amu have been determined, in the limit of zero target thickness, from the thickness variation of the Ti [ital K] x-ray yield with ion beams having 0, 1, or 2 vacancies in their [ital K] shell. From the measured energy shift and the intensity ratios of [ital K][alpha], [ital K][beta] lines, the average number of 2[ital p] and 3[ital p] vacancies were determined from which the average value of the fluorescence yield [omega][sub [ital K]] was deduced using the statistical scaling procedure of Larkins [J. Phys. B 4, L29 (1971)]. The single-electron transfer cross sections are compared with the calculations of Brinkman and Kramer as formulated by Nikolaev [Sov. Phys. JETP 24, 847 (1967)] and those of Lapicki and McDaniel [Phys. Rev. A 22, 1896 (1980)] and the modified two-center atomic-orbital-expansion model (AO+) of Fritsch and Lin [J. Phys. B 15, 1255 (1982)]. The double-electron transfer cross sections are also compared with the AO+ predictions. The [ital K]-shell-vacancy production data are compared with calculations based on the perturbed-stationary-state approachmore » with the Coulomb-deflection, binding-energy, and relativistic corrections (ECPSSR) included. In addition, the projectile cross sections for single-electron capture and loss have also been deduced at a few energies.« less

On the binomial distribution in the theory of inner shell vacancy production by fast ions

A sequential model of multiple vacancy production according to which the vacancies are created in successive collisions of a fast ion with electrons belonging to a definite shell of an atom, with different single electron ionization probabilities, is discussed. A simple formula for the probability distribution of the multiple vacancy production is derived in the framework of this model which must be valid for sufficiently highly charged ions. Comparison of this formula with experiments shows that the sequential model allows discrepancies between the widely used binomial distribution and these experiments to be explained without invoking any fitted parameters.

Foil target element and incident energy dependence of multiple inner shell vacancy production of projectile Ar ions

Foil target element and incident energy dependence of multiple inner shell vacancy production of projectile Ar ions

K-shell vacancy production by direct Coulomb ionization in 47-MeV Ca17++Ar collisions.

Calculations employing the independent-electron approximation suggest that direct Coulomb ionization is the dominant mechanism for Ar K-vacancy production by 47-MeV ${\mathrm{Ca}}^{17+}$, rather than K-K vacancy sharing as proposed by Schlachter et al. [J. Phys. B 21, L291 (1988)]. Using electron-capture probabilities for zero impact parameter given by the classical-trajectory Monte Carlo model, good agreement with the experimental charge-state distribution for multielectron capture in coincidence with Ar and Ca K x rays is achieved.

Charge state and incident energy dependence of K X-ray emission as a function of target thickness for 50–165 MeV Cu ions incident on 11–250 μg/cm 2 Cu

Thin self-supporting Cu targets in 11–250 μg/cm 2 thickness were bombarded with 50–165 MeV Cu q i + ions (7 ⩽ q i ⩽ 24) to investigate the target thickness dependence of inner shell vacancy production processes in the symmetric collision of Cu + Cu. Doppler-shifted projectile K X-rays were discriminated from the target K X-rays, and the projectile and target K X-ray yields were separately measured as a function of target thickness. The K X-ray yields emitted from the projectile and the target Cu atoms are strongly dependent on the projectile initial charge state and target thickness for all the investigated collision systems of Cu q i + + Cu. From the observed K X-ray yields, K-shell vacancy production cross sections averaged over the target thickness t of projectile σ KV and target σ ∗ KV were separately derived taking into account the fluorescence yield that can be estimated from the K α X-ray energy shift. When the values of σ KV and σ ∗ KV are extrapolated to zero foil thickness, the K shell vacancy formed in the collision has been found to be equally shared between projectile and target in a single collision. With the increase of penetration depth, however, the values of σ ∗ KV are greater than those of σ KV presumably due to electron transfer of a target K electron to the projectile K vacancy. the evolution process of projectile excited states as a function of target thickness and the resulting variation of projectile and target K X-ray emissions are discussed.

L-shell andK-shell vacancy production in slow, near-symmetric, and asymmetric ion-atom collisions

Auger-electron production in collisions of slow ${\mathrm{Al}}^{+}$, ${\mathrm{Si}}^{+}$, ${\mathrm{P}}^{+}$, ${\mathrm{S}}^{+}$, ${\mathrm{Cl}}^{+}$, and ${\mathrm{Ar}}^{+}$ ions incident on Ar and ${\mathrm{CH}}_{4}$ targets has been investigated. Total cross sections for projectile L-shell, Ar L-shell, and C K-shell Auger-electron production have been determined experimentally. For a number of cases, vacancy-production cross sections have been deduced by combining the present data with the results of previous x-ray measurements. The latter cross sections are found to be consistent with the predictions of the molecular-orbital model of atomic collisions.

Energy systematics of single and double K-shell-vacancy production in titanium bombarded by chlorine ions.

The energy systematics of single and double K-shell-vacancy production in titanium have been investigated near the limit of zero target thickness for incident chlorine ions over an energy range of 7--15 MeV/amu. Single and double K-shell-vacancy production cross sections have been measured for projectiles incident with zero, one, and two initial K-shell vacancies. Single and double K-shell-to-K-shell electron-transfer cross sections have been obtained indirectly using differencing procedures based on the projectile-charge-state dependence of single and double K-shell-vacancy production. The measured cross sections have been compared to theoretical models for direct ionization and inner-shell electron transfer. Together with previously reported data, these cross sections also have been used to investigate the relative importance of these mechanisms for K-shell-vacancy production in heavy-ion--atom collisions over a range of scaled velocities of 0.24\ensuremath{\le}${V}_{1}$/${V}_{2K}$\ensuremath{\le}1.29.

Total cross sections forL-shell Auger-electron production and vacancy production in slow Si-Ar collisions

Total cross sections for Si $L$ and Ar $L$ Auger-electron production were measured in collisions of 35-500-keV ${\mathrm{Si}}^{+}$ ions incident on Ar atoms, and absolute cross sections for $L$-shell vacancy production were deduced. The experimental results are discussed in terms of the molecular-orbital model of atomic collisions. It is found that electron promotion via the $4f\ensuremath{\sigma}$ molecular orbital is the dominant mechanism for Si $L$-shell vacancy production. Excitation of $3d\ensuremath{\pi}$ and $3d\ensuremath{\sigma}$ electrons via $3d\ensuremath{\delta}\ensuremath{-}3d\ensuremath{\pi}\ensuremath{-}3d\ensuremath{\sigma}$ rotational coupling at small internuclear distances is treated explicitly. The calculated cross section for $3d\ensuremath{\sigma}$ excitation is found to reproduce the experimental cross section for Ar $L$-shell excitation in the range of collision energies up to 200 keV. $L\ensuremath{-}L$ vacancy-sharing processes at large internuclear distances are discussed as possible mechanisms for the observed rise of the Ar $L$ cross section beyond this energy.

Systematics of single and doubleK-shell-vacancy production in titanium bombarded by heavy ions

The systematics of single and double $K$-shell-vacancy production in titanium has been investigated in the limit of zero target thickness (\ensuremath{\sim} 1 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$) for incident C, N, O, F, Mg, Al, Si, S, and Cl ions over a maximum energy range of 0.5 to 6.5 MeV/amu. This corresponds to collision systems with $0.27\ensuremath{\le}\frac{{Z}_{1}}{{Z}_{2}}\ensuremath{\le}0.77$ and $0.24\ensuremath{\le}\frac{{v}_{1}}{{v}_{2 K}}\ensuremath{\le}0.85$, where ${v}_{1}$ is the projectile nuclear velocity and ${v}_{2 K}$ is the mean velocity of an electron in the target $K$ shell. The present work is divided into four major sections. (1) Single $K$-shell-vacancy production has been investigated by measuring $K\ensuremath{\alpha}$ and $K\ensuremath{\beta}$ satellite x-ray-production cross sections for projectiles incident with no $K$-shell vacancies. For incident ions with ${Z}_{1}\ensuremath{\ge}9$, the contribution due to electron-transfer processes from the target $K$ shell to outer shells of the projectile has also been noted. (2) Single $K$---shell-to-$K$-shell electron-transfer cross sections have been obtained indirectly by the measuring of the enhancement in the $\mathrm{Ti}K$ x-ray production cross section for bare incident projectiles over ions incident with no initial $K$-shell vacancies. (3) Double $K$-vacancy production has been investigated by measuring the $K\ensuremath{\alpha}$ hypersatellite intensity in ratio to the total $K\ensuremath{\alpha}$ intensity. (4) Double $K$---shell-to-$K$-shell electron-transfer cross sections have been obtained indirectly with the use of a procedure similar to that used for single $K$ to $K$ transfer. The measured cross sections have been compared to theoretical models for direct Coulomb ionization and inner-shell electron transfer and have been used to investigate the relative importance of these mechanisms for $K$-vacancy production in heavy-ion---atom collisions.

K-shell ionization cross sections for Ti, Cr, Co, Ni, Cu, and Zn targets induced by protons in the energy range 300 — 2400 keV

Absolute $K$-shell x-ray-production cross sections have been measured for thin-foil targets of Ti, Cr, Co, Ni, Cu, and Zn at incident proton beam energies from 300 to 2400 keV. Particular care was necessary in the control of experimental conditions in order to determine the x-ray-production cross sections with high precision (\ensuremath{\sim}5%). The x-ray-production cross sections were determined from x-ray yields normalized to simultaneous measurements of particle scattering yields at 90\ifmmode^\circ\else\textdegree\fi{}. The values of $K$-shell vacancy-production cross sections were determined to range from 0.133 b for 300-keV protons on Zn to 1230 b for 2400-keV protons on Ti. The overall agreement of these total cross sections with recent data obtained by other workers generally is to within 10% and frequently is to within the 5% accuracy of our results. The $K$-shell ionization cross sections inferred from these results are compared with the predictions of energy-loss Coulomb-deflection perturbed-stationary-state relativistic theory which reproduces the data with good accuracy. In addition, these results also show good agreement when compared with a more fundamental formulation based on perturbed-stationary-state theory.

Projectile charge state distributions in close, fast heavy ion-atom collisions: dependence on target thickness and inner shell vacancy production

Charge state distributions of incoming U 40+ ions at 7.5 and 6.7 Mev/ A after scateering to 5° from very thin (1–40 μg/cm 2) Sn targets on 6 μg/cm 2 C backing, as well as their coincidence with U L X-rays and Sn K X-rays have been measured. Even with the thinnest targets the charge distribution at 5° looks similar to equilibrium distributions, with average values of 60+ to 62+. This is in agreement with measurements of lighter ions at lower energies where an equilibrium-like distribution is obtained in a single collision. The average charge increases slightly with target thickness, due to the fact that the single collision mean value is a little lower than the 0° equilibrium one in solid target.

Energy shifts ofKαx rays from highly stripped sulfur ions traveling in solids

The energies and intensities of the $2^{3}P_{1}\ensuremath{\rightarrow}1^{1}S_{0}$, and $2^{1}P_{1}\ensuremath{\rightarrow}1^{1}S_{0}$ transitions in He-like sulfur ions, and of the $2^{2}P\ensuremath{\rightarrow}1^{2}S$ transition in H-like sulfur ions have been studied as a function of the thickness and electron density of the solid through which the ions travel. The thickness dependence of the x-ray intensities was analyzed in terms of a three-component model description of $K$-shell vacancy production and decay. Cross sections for electron excitation or ionization and capture deduced from this analysis were used to establish the energies of the x-ray peaks for complete emission in vacuum (i.e., outside the target). Energy shifts were obtained by comparing the peak energies for emission in thick targets to those for emission in vacuum. The results show that the energy shifts increase approximately linearly with the square root of the valence electron density of the target and are in good agreement with theoretical expectations.