Lα X-ray Production Cross Sections Research Articles

Cross Sections for Inner-Shell Ionization by Electron Impact

An analysis is presented of measured and calculated cross sections for inner-shell ionization by electron impact. We describe the essentials of classical and semiclassical models and of quantum approximations for computing ionization cross sections. The emphasis is on the recent formulation of the distorted-wave Born approximation by Bote and Salvat [Phys. Rev. A 77, 042701 (2008)] that has been used to generate an extensive database of cross sections for the ionization of the K shell and the L and M subshells of all elements from hydrogen to einsteinium (Z = 1 to Z = 99) by electrons and positrons with kinetic energies up to 1 GeV. We describe a systematic method for evaluating cross sections for emission of x rays and Auger electrons based on atomic transition probabilities from the Evaluated Atomic Data Library of Perkins et al. [Lawrence Livermore National Laboratory, UCRL-ID-50400, 1991]. We made an extensive comparison of measured K-shell, L-subshell, and M-subshell ionization cross sections and of Lα x-ray production cross sections with the corresponding calculated cross sections. We identified elements for which there were at least three (for K shells) or two (for L and M subshells) mutually consistent sets of cross-section measurements and for which the cross sections varied with energy as expected by theory. The overall average root-mean-square deviation between the measured and calculated cross sections was 10.9% and the overall average deviation was −2.5%. This degree of agreement between measured and calculated ionization and x-ray production cross sections was considered to be very satisfactory given the difficulties of these measurements.

K-shell ionization cross sections of K and Lα X-ray production cross sections of I by 10–30 keV electron impact

The absolute K-shell ionization cross sections of K and Lα X-ray production cross sections of I by 10–30 keV electron impact have been measured. The target was prepared by evaporating a thin film of compound KI to a thick pure carbon substrate. The effects of multiple scattering of electrons penetrating the target films, electrons reflected from the thick pure carbon substrates and bremsstrahlung photons produced when incident electrons impacted on the targets were corrected by using the Monte Carlo method. For K K-shell and I L-shell X-ray characteristic peaks, the spectra were fitted using the spectrum-fitting program ALLFIT to extract the Kα and Kβ peak counts more accurately for element K, and Lα peak counts for element I. The experimental results were compared with some theoretical results developed recently and available experimental data from the literature. The experimental data for I L-shell X-ray production cross sections by 10–30 keV electron impact are given here for the first time.

Evaluation of cross sections for Lα x-ray production by up to 4 MeV protons in representative elements from silver to uranium

Over the last two decades, Lα x-ray production cross sections have been fitted with a number of empirical formulae. Cross sections obtained from these formulae are averaged and fitted to a new empirical formula. These new empirical cross sections are compared with the results of the plane-wave Born approximation and the ECPSSR theory of Brandt and Lapicki (1981 Phys. Rev. A 23 1717). They are also gauged by the ECPSSR theory that has been corrected with a united atom approach in slow collisions, evaluated with Dirac–Hartree–Slater instead of screened hydrogenic wavefunctions, modified for intra-shell couplings as well as the change of the atomic parameters due to multiple ionizations. The effects of appropriately normalized intra-shell coupling factors and of multiple ionization were found to be small and essentially offset each other. The role of different sets of atomic parameters in conversion of the predictions of these ionization theories for Lα x-ray production in elements from the 47 ⩽ Z2 ⩽ 92 range of target atoms bombarded by up to 4 MeV protons is examined, and the selection of the optimal combination of ionization theory and atomic parameters for a reliable data base for PIXE analysis of elements heavier than palladium is discussed.

Theoretical calculation of Lα X-ray production cross sections of Ga, As, Pt, W and Au atoms by electron impact

The Lα x-ray production cross sections of Ga, As, Pt, W and Au by electron impact are calculated using a modified version of the BELL formula by incorporating both ionic and relativistic corrections in it. The proposed modified Bell model with a single set of parameters can provide an excellent data in the reduced energy range 1≤E/Inl≤106（E and Inl are, respectively, the incident energy and ionization energy） with performance level at least as good as any of the existing methods and models. Experimental data are compared with the present results in cases of with and without the relativistic correction factor GR and the ionic correction factor Fion, with calculated cross sections obtained from the distorted wave Born approximation and with other experimental data available in the literature. The calculated results can be used to simulate the hot-electron energy spectrum and laser plasma yields and accordingly can provide accurate parameters for electron devices.

Angular dependence of Lx-ray production cross sections in seven elements from Yb to Ptat a photon energy of 59.5 keV

The Lℓ, Lα, Lβ and Lγ x-rayproduction cross sections of Pt, Re, W, Ta, Hf, Lu and Yb havebeen measured using an incident photon energy of 59.5 keV atan angular range of 40-130°. The measurements wereperformed using a 241Am radioisotope as the photon source anda detection system with a Si(Li) detector. Althoughdifferential cross sections for Lβ and Lγ x-rayswere found to be angle independent within experimental error,those for the Lℓ and Lα x-rays were found to be angledependent. As previously reported this confirms theangular dependence of photon-induced Lℓ and Lαx-ray production cross sections. Furthermore the present resultsalso confirm the theoretical predictions of Flügge et al (Flügge S, Melhorn W and Schmidt V 1972 Phys. Rev. Lett. 29 7) and Jacobs (Jacobs V L 1972 J. Phys. B: At. Mol. Phys.5 2257). However, our experimental results are contrary to the results reported byMehta et al (Mehta D, Puri S, Singh N, Garg M L andTrehan P N 1999 Phys. Rev. A 59 2723). Integral cross sections forthe production of Lℓ, Lα, Lβ and Lγ x-rays are also deduced inthis paper and are found to be in good agreement withtheoretical values.

Photon-induced L X-ray production differential cross sections in thorium at 22.6 keV

The Ll, Lα, Lβ 2,4, Lβ 1,3 and Lγ 1,5 X-ray production differential cross sections in 90Th have been measured at 22.6 keV incident photon energy in an angular range 50–130°. The measurements were performed using a 109Cd annular-source and a Si(Li) detector. The measured differential cross sections for various L X-rays are found to be angle-independent within experimental error. This is contrary to the strong angular-dependence of photon-induced Ll and Lα X-ray production cross sections as reported by Kahlon et al. (K.S. Kahlon, H.S. Aulakh, N. Singh, R. Mittal, K.L. Allawadhi, B.S. Sood, Phys. Rev. A 43 (1991) 1455) and Ertugrul (M. Ertugrul, Nucl. Instr. and Meth. B 119 (1996) 345). Integral cross sections for production of Ll, Lα, Lη, Lβ 6, Lβ 2,4, Lβ 1,3, Lβ 9,10, Lγ 1,5 and total Lγ X-rays are also deduced and are found to be in good agreement with those calculated using reliable theoretical values of the L i ( i=1, 2, 3) subshell photoionisation cross sections, fluorescence yields, X-ray emission rates and Coster–Kronig transition probabilities.

Projectile charge state dependence of target Lα x-ray production

Lα x-ray production cross sections have been measured for thin solid targets of 60Nd, 67Ho, and 79Au (pt<12 μg/cm2) for 1.86 MeV/amu 199F and 2814Si, and 1.8 MeV/amu 3517Cl ions as a function of the incident charge state. From the projectile charge state dependence of the cross sections, both direct ionization and electron capture contributions were extracted for a comparison to Coulomb ionization theories. The data provide supporting evidence for the theory of electron capture with a reduced binding effect.

Sensitivity and Detectability Limits for Elemental Analysis by Proton-Induced X-Ray Fluorescence with A 3 Mv Van De Graaff

AbstractProtons from a 3 MV Van de Graaff have been used to produce characteristic x-rays from 21 elements spanning the periodic table. Absolute Kα and Lα x-ray production cross sections have been determined, allowing one to calculate sensitivities for any given sample, detector geometry, and proton beam parameters. Elemental detectability limits are discussed assuming various backings (e.g., mylar, kapton, etc.) and matrix materials. The large number of available small proton accelerators throughout the United States promises wide applicability of this technique to environmental and biomedical analysis.