X-ray Production In Targets Research Articles

TargetK-vacancy production by2.5to25MeV∕amuAr, Kr, and Xe ions

Cross sections have been measured for $K\ensuremath{\alpha}$ x-ray production in targets of Al, Ti, Cu, Zr, Ag, Sm, and Ta by Ar, Kr, and Xe ions ranging in energy from $2.5\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}25\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\mathrm{amu}$. In addition, the degree of simultaneous $L$-shell ionization and the enhancement of the $K\ensuremath{\alpha}$ diagram lines due to secondary ionization processes were assessed by performing high-resolution spectral measurements on Al, Ti, V, Co, and Cu targets. This information was used to correct for the $K\ensuremath{\alpha}$ x-ray yield produced by electron bombardment and photoionization, and to calculate the fluorescence yields needed to convert the $K\ensuremath{\alpha}$ x-ray production cross sections into $K$-vacancy production cross sections. The resulting cross sections were compared with the predictions of the perturbed stationary state approximation with corrections for projectile energy loss, Coulomb deflection, and relativistic effects (ECPSSR theory). Also, the scaling properties of the $K\ensuremath{\alpha}$ x-ray production cross sections were examined and a semiempirical (universal) curve was deduced that reproduces the measured cross sections to within $\ifmmode\pm\else\textpm\fi{}30%$ on average.

Charge-state dependence of K-shell x-ray production in aluminum by 2-12-MeV carbon ions.

Charge-state dependence for {ital K}-shell x-ray production cross sections in {sub 13}Al bombarded by 2{endash}12-MeV {sub 6}C ions with charge states from 2+ to 6+ was measured using a Si(Li) detector. A thin Al target was used to ensure single collision conditions. Contributions of the electron capture as well as direct ionization to the inner-shell ionization were determined by an analysis of the charge-state dependence of the target x-ray production. The measurements are compared with the prediction of the ECPSSR theory using a single-hole fluorescence yield. The ECPSSR theory is based on the perturbed stationary state (PSS) formalism and relativistic effects (R) for the target electrons, and energy loss (E) and Coulomb deflection (C) of the projectile. In general, this theory gives reasonable agreement with the data for carbon ions without {ital K} vacancies while it overpredicts the data for carbon ions with {ital K} vacancies. The significant underprediction of the data at the lowest energy is likely associated with the molecular-orbital effect that is not accounted for in the ECPSSR theory. {copyright} {ital 1996 The American Physical Society.}

Charge-state dependence of M-shell x-ray production in 67Ho by 2-12-MeV carbon ions.

Charge-state dependence of M-shell x-ray production cross sections of $_{67}\mathrm{Ho}$ bombarded by 2--12-MeV carbon ions, with and without K-shell vacancies, were measured using a windowless Si(Li) x-ray detector with a full-width-at-half-maximum resolution of 135 eV at 5.9 keV. Carbon ions of different charge states were produced using a postacceleration, nitrogen gas stripping cell. The carbon ions were then magnetically analyzed to select the desired charge state and energy before entering the target chamber. The total M-shell and M\ensuremath{\zeta}, M\ensuremath{\alpha},\ensuremath{\beta}, and M\ensuremath{\gamma} x-ray cross sections were measured. The electron-capture (EC) contributions as well as the direct-ionization (DI) contributions can be determined by making a comprehensive study of the projectile-charge-state dependence of the target x-ray production cross sections for targets in which the single-collision realm is maintained. In this paper, both EC and DI contributions and the total M-shell x-ray production cross sections are compared to both the first Born theory and to the perturbed-stationary-state theory with energy-loss, Coulomb-deflection, and relativistic corrections.

CHARGE DISTRIBUTIONS OF FAST PROJECTILES IN LOW-Z MATERIALS

For an accurate calculation of target x-ray production or of projectile energy loss in low-Z materials, it is necessary to know the projectile charge state at each point in the material. If the projectile is fast enough so that charge transfer can be neglected with respect to electron stripping, it is possible to deduce a simple expression for the charge fractions as a function of the penetration distance into the target. The expression depends essentially only on the stripping cross section per electron of the particular shell being stripped, on the initial number of electrons on the projectile, and on the charge state. A small correction has to be applied for the effect of shells lying inside of the shell being stripped. The expression has been tested with Xe45+ projectiles between 82 and 300 MeV/u and with U83+ projectiles between 105 and 960 MeV/u with targets of Be, C, mylar, and Al. Model calculations are made of the effect of charge distributions on PIXE x-ray production and on projectile energy loss.

Implications of heavy-ion-induced satellite X-ray emission II: Production of K and L X-rays by 0.9–2.6 MeV/u Argon Ions in Thick Targets of vanadium, copper, niobium, tantalum and platinum

Cross sections are reported for X-ray production in targets of 23V, 29Cu, 41Nb, 73Ta, and 78Pt by 40Ar ions of 36.0, 56.4, 76.6 and 103 MeV. Because the targets were relatively thick, ∼1 mg/cm 2, the data were corrected - using a novel approach - for projectile energy loss and X-ray attenuation in the targets. The cross sections so analyzed are compared with the predictions of the first Born approximation as well as with those of a more extensive treatment which includes energy loss. Coulomb deflection, perturbed stationary-state, and relativistic effects. The significant discrepancies between the data and this latter theory are attributed primarily to the influence of multiple ionization on the X-ray emission probabilities.

Projectile Charge State Dependence of M-Shell Ionization of Au, Pb, Bi and U by 1.42-MeV/amu Fluorine Ions

The present study was undertaken to determine the direct ionization and electron capture contributions to vacancy production in the M-shells of 79Au, 82Pb, 83Bi and 92U for incident 199F ions. M-shell x-ray production cross sections have been measured for 1.42-MeV/amu 199Fq+ ions for q=4,5,6,8,9. Enhancements in the target x-ray production cross sections were observed for projectiles with one and two K-shell vacancies over those without K-shell vacancies. Direct ionization and electron capture contributions to the vacancy production were extracted from the data and compared to the plane wave Born approximation and to the Oppenheimer-Brinkman-Kramers calculations of Nikolaev, respectively.

Target thickness dependence of CuKx-ray production for ions moving in thin solid Cu targets

Measurements of the target thickness dependence of the target x-ray production yield for incident heavy ions at 1.71 MeV/amu are reported for thin solid Cu targets. The incident ions were F, Al, Si, and S. The charge states of the incident ions were varied in each case to study the target x-ray production for projectiles which have initial charge states $q$ of $q={Z}_{1}$, $q={Z}_{1}\ensuremath{-}1$, and $q<{Z}_{1}\ensuremath{-}1$. The target thicknesses were varied from 3 to 85 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$. In each case the Cu $K$ x-ray yields exhibit a complex exponential dependence on target thickness. A three-component model which includes contributions to the target x-ray production due to ions with zero, one, and two $K$ vacancies is developed to describe the observed target $K$ x-ray yields. The three-component model is fitted to the individual data for each projectile, and the cross sections for both the target and projectile are determined. The fits to the target x-ray data give a systematic representation of the processes involved in x-ray production for heavy ions incident on solid targets.

Evidence for thin-target X-ray emission in a small solar flare on 26 February 1972

We compare solar X-ray observations from the UCSD experiment aboard OSO-7 with high resolution energetic electron observations from the UCAL experiment on IMP-6 for a small solar flare on 26 February 1972. A proportional counter and NaI scintillator covered the X-ray energy range 5–300 keV, while a semiconductor detector telescope covered electrons from 18 to ∼ 400 keV. A series of four non-thermal X-ray spikes were observed from 1805 to 1814 UT with average spectrum dJ/d (hv) ∼ (hv)−4.0 over the 14–64 keV range. The energetic electrons were observed at 1 AU beginning 1840 UT with a spectrum dJ/dE ∼ E−3.1. If the electrons which produce the X-ray emission and those observed at 1 AU are assumed to originate in a common source, then these observations are consistent with thin target X-ray production at the Sun and inconsistent with thick target production. Under a model consistent with the observed soft X-ray emission, we obtain quantitative estimates of the total energy, total number, escape efficiency, and energy lost in collisions for the energetic electrons.

Dependence of X-Ray Yields in Argon, Krypton, and Xenon upon the Charge State of Fluorine Ions at 35.7 MeV

In high-velocity ion-atom single collisions, a strong dependence of target x-ray production cross sections upon the ionic charge state has been observed. Experiments were performed in thin gas targets of argon, krypton, and xenon with 35.7-MeV fluorine ions incident in charge states +5 to +9. Production cross sections for Ar $K$, Kr $L$, and Xe $L$ characteristic lines increase by as much as a factor of 5 with increasing incident charge state but cannot be fitted by a ${q}^{2}$ dependence.