X-ray Emission Cross Sections Research Articles

Comments on experimental deuteron-induced K X-ray emission cross sections

In a recent publication, (1982), Barfoot et al. accurately measured (+or-6%) the K X-ray emission cross sections for selected targets between Ti and Ge in the ion energy range 1 to 3 MeV. Comparisons with the PWBABCR theory were made and a small ion-energy-dependent deviation from theory suggested. The authors suggest that by using the more recent ECPSSR theory and a better, more recent, data base for the K-shell fluorescence yields and branching ratios, this energy-dependent deviation is completely removed and the agreement between the theory and the results of Barfoot considerably improved. In fact, the ratio of experiment to theory was (1.01+or-0.03), well within the (+or-6%) experimental accuracy.

Charge Exchange Collision Experiments With Highly Charged Ions -Status Report-

In the collision of highly charged ions on atoms or simple molecules, one electron (or more) may be transferred to the projectile. It is observed that in the low velocity range (ν < ν0), the one electron charge exchange cross-section is quasi energy independent at least in the energy range 2q-10q keV when q ⩾ 4. It is shown that a scaling law may be deduced from a series of measured values obtained with Cq+, Nq+, Oq+, Arq+, Xeq+, some of them up to completely stripped (C, N, O; Ar up to q = 16).Since the collision may be described along quasi-molecular approaches, it is known that the projectile after capture is left in excited states. An attempt is made to observe part of the radiative decay in the case of the capture of one electron by completely stripped C, O and Ne ions which are thus left hydrogenic and radiate in the soft X-ray range. The X-ray emission cross section is shown to be large and may be utilized to calculate the excitation cross-section for a given level.

Experimental deuteron-induced K X-ray emission cross sections

K X-ray emission cross sections have been measured to an uncertainty of +or-6% for 1 to 3 MeV deuterons incident on thin layers of selected elements with atomic number (Z2) from 22 to 32. The experimental technique is outlined and the results compared with the predictions of modifications to the plane-wave Born approximation (PWBA) and the semiclassical approximation (SCA). Agreement is better with the PWBA, corrected for 'binding energy' and 'Coulomb' effects, with the theory underestimating the data by only 12% on the average. This deviation exhibits negligible projectile energy or Z2 dependence.

Target thickness dependence of projectile K X-ray emission in fast heavy ion bombardments on carbon foils

Heavy projectile K X-ray emission yields have been measured as a function of carbon target thickness for incident ions of 40 MeV Cl 13+, 95 MeV Cl 8+, 12+, 15+, 16+, 17+, 115 MeV Fe 10+, 120 MeV Cu 11+, 150 MeV Cu 13+ and 140 MeV Br 12+. In the thin target foil region where the loss and capture process of projectile L shell electrons is not equilibrated, projectile K X-ray emission cross sections have been found to be significantly influenced by the variation of the number of projectile L shell electrons.

Contribution to the 1sσ continuum radiation from single and double collisions in the O and N systems

The authors have measured 1s sigma X-ray emission cross sections for the symmetric collision systems O+ to H2O, O2 between 300 keV and 1.45 MeV bombarding energy and for the asymmetric collision systems O+ to N2, NH3 and N+ to O2, H2O at 300 keV. For the O+N systems, the 1s sigma cross section is insensitive to target gas type. This result is markedly different from that found for symmetric O+ to O2, H2O collisions at 300 keV where the 1s sigma emission cross section for target O2 molecules exceeds that for H2O by a factor of ten. However, at higher velocities (0.5-1.45 MeV), the single-collision contribution to 1s sigma emission dominates. All results are in qualitative agreement with the molecular orbital description of X-ray production in atomic collisions.

Threshold behavior of Cu-, Ge-,Ag−K−, andAu−L3-shell ionization cross sections by electron impact

Electron-induced Cu-, Ge-, $\mathrm{A}\mathrm{g}\ensuremath{-}K$ shells, and $\mathrm{A}\mathrm{u}\ensuremath{-}{L}_{3}$-shell ionization cross sections have been obtained from the measurement of $K\ensuremath{\alpha}$ and $L\ensuremath{\alpha}$ x-ray emission cross sections around the threshold energy. $K$- and ${L}_{3}$-shell ionization cross sections have been observed to rise as a function of $\mathrm{ln}\frac{({U}_{i})}{{U}_{i}}$, where ${U}_{i}$ is the ratio of electron impact energy to ionization energy. In the increasing behavior of $\mathrm{A}\mathrm{u}\ensuremath{-}L\ensuremath{\alpha}$ and $\ensuremath{-}L\ensuremath{\beta}$ x-ray emission cross sections with increasing impact energies, the onset of ${L}_{2}$- and ${L}_{1}$-shell ionizations have been observed at ${L}_{2}$- and ${L}_{1}$-shell ionization energies. Absolute values of Cu-, Ge-, $\mathrm{A}\mathrm{g}\ensuremath{-}K$-shell ionization cross sections are well reproduced by the empirical formula of Green and Cosslett down to the vicinity of threshold energy.

Sensitivity in light element analysis by 2 MeV and 150 keV proton and photon induced X-rays

The sensitivity of low energy proton induced X-ray emission analysis using a simple low energy accelerator has been compared with high energy proton or photon excitation for the analysis of trace elements with atomic number less than about 20. For low energy proton impact, characteristic X-ray emission cross sections are lower than those of 2 MeV protons but the bremsstrahlung from secondary electrons is much lower than that of 2 MeV proton impact in the X-ray energy range lower than about 5 keV. As a result the sensitivity of trace element analysis for Z≦18 is higher for 150 keV than for 2 MeV proton excitation. Photon sources are considered as a competitive way of excitation for relatively large samples such as pellets.

X-ray emission cross sections for carbon bombarded with 4- to 40-MeV C, N, and O ions

Cross sections for production of target-atom carbon $K$ x rays in thin evaporated carbon films are determined from spectra obtained using a double-focusing soft-x-ray spectrometer with calibrated transmission. A maximum value of 2.3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}19}$ ${\mathrm{cm}}^{2}$ is found for 18-MeV oxygen ions. A maximum ionization cross section of 4.8 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}17}$ ${\mathrm{cm}}^{2}$ is estimated from the data. Cross sections for x rays on both sides of the carbon $K$ edge are determined. Nitrogen ions produce more $L$-shell ionization at low energies than carbon or oxygen ions, both of which create very few $K{L}^{2}$ satellite x rays below about 9 MeV.

Carbon, nitrogen, neon and argon K-shell ionization by proton and helium-ion impact: X-ray emission cross sections and fluorescence yields

K-shell X-ray emission cross sections are determined for gas targets (methane, nitrogen, neon, argon) ionized by H+, He+ and He2+ impact (energies from 100 to 2400 keV). The fluorescence yield for carbon, nitrogen and neon is calculated using known Auger cross sections; the absolute uncertainty is 20-30%, the relative values are determined within 5-10%. The impact-energy dependences of the fluorescence yields and of the detection efficiencies are measured. Both increase with decreasing impact energy. Values of the ionization cross sections are compared with BEA and PWBA calculations. The latter, corrected for binding, polarization and Coulomb deflection effects, are in reasonable agreement with experiment, especially for the projectile ratios (ratios of cross sections for He+ compared with H+ impact).

X-ray emission cross sections and spectral distributions for carbon bombarded with MeV C, N, and O ions

X rays emitted by a thin target bombarded with C, N, and O ions with energies between 1 and 2.5 MeV are observed at an angle of 135\ifmmode^\circ\else\textdegree\fi{} with a Bragg crystal spectrometer having a resolution of 3 eV. The $\mathrm{KL}$ and $K{L}^{2}$ satellite lines of the carbon target are observed, as well as the diagram $K$ line. These peaks are superimposed on a broad x-ray distribution extending from 265 to 290 eV. The $K{L}^{2}$ line appears for N at low energies, but not for C. Projectile and target spectra involve the $K$ and $\mathrm{KL}$ lines in approximately equal amounts for C. These observations are interpreted as evidence for a molecular-orbital theory involving promotion of $L$ electrons of the colliding atoms, in which the momentum change of the promoted electron is taken into account. Cross sections for production of carbon $K$ x rays at energies below the carbon absorption edge in the Bragg pseudocrystal are obtained from the data. The cross sections rise monotonically with energy in the range studied and are smallest for oxygen ions, which have the largest atomic number.

Projectile-charge dependence of theKx-ray emission cross section of carbon bombarded by megavolt nitrogen ions

The carbon $K$ x-ray emission cross section of methane molecules bombarded by 1- to 5-MeV nitrogen ions has been measured for incident charges +2 to +5 under single-collision conditions. Only x rays with energies which penetrate the polypropylene window of a proportional counter are counted. The cross sections increase monotonically with ion energy. Above 2 MeV they also increase with ion charge, to a maximum of nearly ${10}^{\ensuremath{-}18}$ ${\mathrm{cm}}^{2}$.

An ion-implantation method to measure the fraction of beam carrying inner-shell vacancies when penetrating solids

It is shown that from the Ar K-shell X-ray emission cross-section in collisions of Ar projectiles with Ar atoms, previously implanted in Si, one can determine the fraction of beam carrying L-shell vacancies. The depth dependence of this fraction can be obtained by varying the implantation energy. The results yield quantitative information on L-shell vacancy lifetimes of Ar ions moving through solids.

Ar L-shell ionization by electrons and light ions: determination of X-ray emission cross sections and mean fluorescence yields for charge-state distributions

The absolute cross sections for ArL2.3 X-ray emission have been measured for 0.25-14 keV electrons, 30-500 keV protons, 30-150 keV H2+, 30-800 keV He+, and 600-2000 keV alpha particles, incident on argon gas. Experimental problems associated with absolute measurements of the X-ray cross sections, particularly the detection efficiency, are discussed. In order to calculate mean fluorescence yields the X-ray data have been compared with available L2.3 Auger-electron-ejection cross sections; the accuracy of the absolute fluorescence yields obtained is about 37%. An extensive analysis is presented on the outer-shell charged-state distributions of the Ar L ions formed, considering the fraction of normal Auger transitions, the different types of excitation mechanisms and some empirical models.

Measurements of the L-shell fluorescence yields of Ar and Cl by electron impact

L-shell X-ray emission cross sections have been measured for 1 keV electron impact on Ar, HCl and Cl2. The fluorescence yields derived from these cross sections and known Auger emission cross sections are significantly smaller than results of recent theoretical calculations of the fluorescence yields for configurations with more than one open shell. This indicates that the assumption of statistical population of the initial spectroscopic terms when calculating mean fluorescence yields is invalid.

Kx-ray emission from 20- to 36-MeV fluorine projectiles following electron capture to excited states

The projectile $K$ x-ray emission cross sections for fluorine ions were measured under single collision conditions for charge states ranging from +4 to +9 in a thin argon target. The dependence of these cross sections upon the energy and the initial charge state of the projectile was determined for fluorine ions with energies between 20 and 36 MeV. Over the entire energy range, the $K$ x-ray---production cross section for ${\mathrm{F}}^{+9}$ ions was about 70% of the total electron-capture cross section determined in a separate experiment. The $K$ x-ray---production cross section for these fully stripped ions is attributed to electron capture to excited states of the projectile. Calculations of electron-capture cross sections within the Brinkman-Kramers approximation for these heavy-ion collisions are consistent with the observation of large cross sections for capture to excited states.

Investigation of Elemental Analysis of Water Samples by Radioalpha Induced X-Ray Emission Spectroscopy*

AbstractAlpha particles and protons from charged particle accelerators and photons from both x-ray tubes and radioactive sources have been shown to be useful for the excitation of characteristic x-rays for multi-element energy dispersive trace analysis of environmental samples to the few ppm range. We have investigated the use of 4.5 MeV alpha particles from a thin window Po-210 source of 5 mCi effective strength to directly excite x-rays from trace elements in 1 cc water samples evaporated on 1.75 mg/cm2 thick mylar backings in a helium atmosphere in a lucite enclosure. Minimum detectable amounts (MDA's) were established for 19 elements (22 ≤ Z ≤ 82) using K-, L- and M- radiation and 50 minute counting times. The smallest MDA determined was 0.11 μg for vanadium. Other representative MDA's, in μg, are Fe-0.54, Mo-0.31 and Pb-0.43. MDA's lower by an average factor of about 10 over an eight month source life would result from the use of 1 Ci of Po-210 for 50 minutes per sample. Thinner sample backings and improved source encapsulation will reduce background radiation and further improve sensitivity. Comparison of our MDA's (5 mCi-Po-210) with those of Blasius et al., who used radiophoton sources and 40,000 sec. counting times to determine trace metal pollutants in water samples, shows radioalpha excitation to have comparable sensitivity in the worst case, arsenic and better, by more than two orders of magnitude, sensitivity in the best case, vanadium.Radioalpha induced x-ray trace element analysis offers the same advantages of portability, ease of operation, low maintenance and cost, and "in house" availability as radiophoton induced analysis. Because of the availability of more intense sources (up to 10 Ci), the fact that the detected radiation (x-rays) differs from the excitation radiation (a-particles) and that K, L, and M x-ray emission cross-sections depend essentially only on the emitted x-ray energy, lower MDA's are obtainable for many elements in thin samples for comparable counting times, as well.

K-shell X-ray emission cross sections and ionization cross sections for light atoms and molecules by H +, H +2 and He + impact at 30–145 keV

The cross sections for K-shell X-ray emission have been measured for 30–145 keV H +, H + 2 and He + ions incident on the gases CH 4, CO, N 2, Ne and Ar. Using values for the fluorescence yields derived from similar electron impact experiments, in which the same gas targets were used, the ionization cross sections for these K-shells by proton impact have been deduced. The values thus obtained show reasonable agreement with the Auger-electron measurments of Stolterfoht for the gases CH 4 and N 2 in the energy range of overlap, 50–145 keV. For the lightest elements, C and N (in CH 4 and N 2), the K-shell ionization cross sections agree reasonably with the Born theory for ionization at the highest energies used. For Ne and Ar, with larger K-shell binding energies, and at low energies for C and N, the experimental cross sections are much smaller than the ones calculated by the Born approximation. These results are better described by the ionization theory of Brandt including Coulomb repulsion, binding and polarization effects, and the binary encounter theory of Garcia, which includes Coulomb repulsion effects. The contribution of electron-capture processes to the K-shell ionization cross sections is discussed.

X-ray emission cross sections and fluorescence yields for light atoms and molecules by electron impact

The cross sections for K-shell X-ray emission have been measured for 0.2–18 keV electrons incident on CH 4, N 2, O 2, Ne and Ar. The measurements are compared with available K-shell Auger-electron ejection cross sections (between 0.5 and 11 keV) in order to deduce the fluorescence yields (ω K) for these shells. It is found that there is no dependence of ω K on the incident electron energy, and the experimental values are in good agreement with recent theoretical calculations of Walters and Bhalla. The influence of simultaneous inner- and outer-shell ionization, shake-off effects and the molecular environment on the fluorescence yields is discussed.

The influence of outer-shell excitation on the X-ray production in ion-atom collisions

Recent experimental results on X-ray production in ion-atom collisions are discussed. It is suggested that the state of the outer-shell strongly influences the X-ray emission cross sections, particularly if one applies solid targets.