K X-ray production cross sections for 40-180 keV protons

Considering the importance of the X-ray production cross sections for the determination of the element concentrations in a given material, we have measured them experimentally for Al Si, Sc, Ti, V, Fe, Co, Ni and Cu bombarded by protons with energies ranging from 40 to 180 keV. This revised version was published online in July 2006 with corrections to the Cover Date.     

Collision cross sections for protein ions

A method for the determination of cross sections for gas-phase protein ions, based on the energy loss of ions as they pass through a collision gas, is described. A simple model relates the energy loss to the number of collisions and hence the cross section. Results from a Monte Carlo model that support the validity of this approach are described. Experimental cross sections are reported for motilin, ubiquitin, cytochrome c, myoglobm, and bovine serum albumin. Cross sections range from approximately 800 Ų for motilin to approximately 14,000 Ų for bovine serum albumin and generally increase with the number of charges on the ion. Cytochrome c ions from aqueous solution show somewhat smaller cross sections than ions formed from solutions of higher organic content, suggesting that the gas-phase ions may retain some memory of their solution conformation.     

Measurement of Cu K and Ag,In and Sn L X-ray production cross sections by low-energy positron impact

Cu K and Ag, In and Sn L X-ray production cross sections by positron impact have been determined experimentally in the energy range below 30 keV using an X-ray detector with thin Si(Li) crystals. These values have been compared with theoretical estimates derived using the binary encounter formalism. The values for Cu K and Ag L X-rays have also been compared with the results of theoretical calculations using the plane-wave Born approximation with Coulomb and relativistic corrections.     

Measurement of angular dependencies of M X-ray differential cross sections and production cross sections using 5.96 keV photons

The differential cross sections of the emission of M-shell fluorescence X-rays from Tl and Pb have been measured by 5.96 keV photons at seven angles ranging from 50° to 110°. The differential cross section is found to decrease with the increasing emission angle, showing an anisotropic spatial distribution of M-shell fluorescence X-rays. Furthermore, M-shell fluorescence cross sections and the average fluorescence yields were measured for Pt, Au, Hg, Tl, Pb, Bi, Th, and U at an excitation energy of 5.96 keV using a Si(Li) detector. The experimental results of the total M X-ray fluorescence cross sections and M-shell fluorescence yields were compared with the theoretical values.This revised version was published online in November 2005 with corrections to the Cover Date.     

Multiple ionization effects on total L-shell X-ray production cross sections by proton impact

The effect of multiple ionization on total L-shell X-ray production cross sections by proton impact, with energies below 1 MeV, on elements with atomic numbers in the range 26–55 was studied. Measurements of those cross sections for several elements were also done to enlarge the experimental database. Several tables for atomic parameters (fluorescence yields and Coster–Kronig transition probabilities) were used. The agreement between theory and experiment was optimized when average fluorescence yields given by Hubbel et al. (J. Phys. Chem. Ref. Data 23(2) (1994) 339) and a multiple ionization model proposed by Lapicki et al. (Phys. Rev. A 34(5) (1986) 5813) were used together. Thus, improvements to theoretical predictions for ionization cross sections should consider first a correct set of atomic parameters.     

New procedure calculation of K-shell ionization cross sections by proton impact

The database, which relies on different compilations available in the literature and on other experimental values extracted from papers published from 1992 till 2010, is used, within the individual treatment of the elements from beryllium (⁴Be) to uranium (⁹²U), to deduce the empirical cross sections. These experimental data can be presented in a single curve, depending on a scaling law extracted from studies in the most familiar theories of collision (PWBA and BEA). Then, a fourth order polynomial was used to fit very well the existing database of K-shell ionization cross sections by proton. This procedure generates a new set of parameters to calculate empirical cross sections. Following the present procedure, our results are compared with those obtained using the ECPSSR model where a discrepancy is observed in the low-proton energy regime.     

Photon and proton induced X-ray cross sections for some elements

The cross sections for the production of K and L shell x-rays in some elements by monoenergetic photons have been measured and the experimental values were compared with the theoretical values. Also, the K shell x-ray production cross sections have been measured for thin targets of some elements by protons over the energy range 1.5–3.0 MeV. The ionisation cross sections were calculated and compared with Johansson's empirical formula.     

Differential cross sections for collisions of negative halogen ions and alkali atoms

In this paper we present the relative differential cross sections for collisions of several negative halogen ions with Na and K. The measurements have been carried out in two separate experiments with energy ranges of 5–150 eV and 500–1000 eV and angular ranges of 0-35° and 0-0.3°, respectively. It is shown that in both of these experiments elastic scattering is the dominant process. No significant inelastic contribution to the differetial cross section, especially no electron detachment, has been observed. The measured differential cross sections are used to obtain information on the anion intermolecular potentials. Comparison of these potentials with the potentials of the neutral molecules shows that all systems investigated have a positive electron affinity over a wide range of internuclear distances. An approximately linear relationship between the dipole moments and the electron affinities is obtained for the halides of the specific alkalis.     

Nonresonant charge transfer: Semiclassical calculation of differential cross sections

Charge transfer and elastic scattering differential cross sections in Li⁺ + Na are described in a two state model by a consequent application of semiclassical methods. The coupling model used is Demkov coupling; coupling parameters and potential curves are taken from calculations of other authors. The theoretical results, which contain no adjustable parameters, are in good agreement with experiment.     

Integral cross sections for electronic excitation in KHg collisions

The energy dependence of the integral cross section for the electronic excitation in collisions of K and Hg is investigated for energies between 50 eV and 1500 eV. By the measurement of the spectra of the emitted light the 4²P_{$\text{3}\text{2}$} and the 4²P_{$\text{1}\text{2}$} states of potassium are found to be dominant. For these the energy dependence of the cross sections is studied in detail. By the measurement of the polarization the contributions to the 4²P_{$\text{3}\text{2}$} state are differentiated with respect to |m_j|.     

Tchebycheff-derivative approximations to photoabsorption cross sections in atoms and ions

Spectral moments and Tchebycheff's inequalities are employed in the construction of continuous, convergent approximations to photoabsorption and ionization cross sections in atoms and ions.     

Evaluation of cross sections for X-ray and high-energy electron scattering from molecular systems

An analytical and computationally efficient formalism for the evaluation of rotationally averaged cross sections for X-ray and high-energy electron scattering from molecular systems is given. Its application for both SCF and CI wave functions is discussed. © 1994 John Wiley & Sons, Inc.     

Chemical effects on K and L shell production cross sections and transfer probabilities in Nb compounds

In this study, the chemical effects on σ_Ki (i = α, β), σ_Lα cross sections, K_β/K_α X-ray intensity ratios and vacancy transfer probabilities from K to L (η _KL) for pure Nb and Nb compounds were investigated. The samples were excited by 59.5 keV γ-rays from ²⁴¹Am and 5.96 keV photon energy from a ⁵⁵Fe annular radioactive sources. K and L X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV. While it was observed that the chemical bonding had an effect on the σ_Kβ, σ_Lα cross sections and K_β/K_α X-ray intensity ratios for compounds, it was almost negligible for σ_Kα cross section because K_α transitions (2P_3/2,1/2→1S_1/2) occurred in inner shells. It is well known that interactions between central element atom and ligands come into existence in valence state, so outer energy levels are sensitive to the chemical environment. The experimental values of σ_Kα cross section and η _KL are in good agreement with theoretically calculated and other experimental values of pure niobium, but the experimental values of the σ_Kβ, σ_Lα cross sections and K_β/K_α X-ray intensity ratios have differences for some compounds because valence electrons have different bond distances and binding energies in different compounds.     

Measurement of impact parameter dependent probabilities and total cross sections for targetK-shell ionization by He+ ions

We have measured the impact parameter dependent K-shell ionization probabilitiesP _K (b) of Ca, Cr and Cu from collisions with 4.04 MeV He⁺ ions by particle-K X ray coincidences. A dependence on the target thickness was investigated to study a possible influence of multiple collisions onP _K (b). We measured the total cross section σ _K forK vacancy production simultaneously withP _K (b) and σ _K agrees within 30% with the integratedP _K (b). A comparison of theP _K (b) and σ _K with SCA calculations of Trautmann et al. using RHFS wavefunctions for united atom and separated atom states is discussed.     

Semiempirical calculation of photoionization cross sections for the first excited levels of F I

Radial matrix elements and photoionization cross sections have been calculated for all levels of the first excited configuration 2p ⁴(³ P) 3s of neutral fluorine as an example for the application of the Scaled Thomas-Fermi method. The extrapolation of empirical data on energy levels to positive electron energies and the reliability of the method are discussed.     

L X-ray production cross sections, average L shell fluorescence yield and intensity ratios in heavy elements

L X-ray fluorescence cross sections, and intensity ratios were measured for elements in the 70￡Z￡92 atomic range at the excitation energy 59.5 keV using a Si(Li) detector. Furthermore, L X-ray fluorescence cross sections and intensity ratios were calculated for elements in the same range. The average L shell fluorescence yields were derived using experimental L X-ray fluorescence cross sections and theoretical photoionization cross sections. The obtained results were compared with other experimental and theoretical values. This revised version was published online in August 2006 with corrections to the Cover Date.     

Measurements of K X-ray fluorescence cross sections of Fe,Co, and Ni in an external magnetic field

The effects of the external magnetic field has been investigated on the K XRF cross sections of Fe, Co, Ni, and some of their compounds by using an energy dispersive X-ray fluorescence spectrometer. The samples were irradiated by using the γ-rays of 59.537 keV emitted from an ²⁴¹Am radioisotope source of 100 mCi. The samples were prepared from pure foil of Fe, Co, Ni, and some of their compounds. The external magnetic fields have been applied two opposite directions and the magnitude of the external magnetic field has been fixed at 0.400 T and −0.400 T. The measured K XRF cross sections have been compared with the calculated theoretical data and interpolated values of Puri et al. Our experimental results show that the K XRF cross sections have been affected by the external magnetic field.