Low-energy electron elastic collision cross sections for ground and excited Tm, Lu and Hf atoms

Low-energy 0 ? E ? 1.0 eV electron elastic scattering from ground and excited Tm, Lu and Hf atoms has been investigated. Both total and differential cross sections have been calculated; the latter at the scattering angles θ = 0°, 90° and 180°. The recent Regge-pole methodology has been used for the calculations. In the method the crucial electron-electron correlation effects are accounted for through the Mulholland formula. We find that the total cross sections are characterized generally by shape resonances, Ramsauer-Townsend minima and dramatically sharp long-lived resonances from which we extract the binding energies of the negative ions. Our extracted binding energy of the Hf⁻ negative ion from the total cross section is compared with that of Pan and Beck [14].     

Measurements of the elastic scattering cross sections for proton on T, He

The cross sections for the elastic scattering of protons from tritium at 151° and from helium at 155° angles in the laboratory frame, over the energy range of 1.2-3.4 MeV, have been measured in the present work, as a supplement to previous cross section measurements determined at different scattering angles recently. The currently measured cross section data are compared to data available in literature. The cross section enhancement was also investigated for both reactions. It was found that over the whole measured energy range, the elastic cross section for protons on tritium increases linearly with energy and is about 1000 times greater than the Rutherford cross section at 3.4 MeV. On the other hand, in the case of the elastic scattering of protons from helium, the cross section below 2.3 MeV increases almost linearly, and reaches a maximum of about 300 mb/str at the energy of 2.4 MeV for the scattering angle of 165°, and then, after this energy, it keeps oscillating around the maximum.     

Electron-impact excitation and ionization cross sections for ground state and excited helium atoms

Comprehensive and critically assessed cross sections for the electron-impact excitation and ionization of ground state and excited helium atoms are presented. All states (atomic terms) with n4 are treated individually, while the states with n5 are considered degenerate. For the processes involving transitions to and from n5 levels, suitable cross section scaling relations are presented. For a large number of transitions, from both ground and excited states, convergent close coupling calculations were performed to achieve a high accuracy of the data. The evaluated/recommended cross section data are presented by analytic fit functions, which preserve the correct asymptotic behavior of the cross sections. The cross sections are also displayed in graphical form.     

An empirical expression for total scattering cross sections of normal hydrocarbons, and experimental total cross sections of C2H2 and C3H4

The total electron scattering cross sections (TCS) of C₂H₂ and C₃H₄ have been obtained for 200-4500 eV electrons by measuring the attenuation of the electron beam through a gas cell. An empirical expression is deduced to express the TCS of normal hydrocarbons as a function of the number of atomic constituencies in the hydrocarbon and the electron energy.     

Differential elastic scattering cross sections of protons from Al in 2.4–4.8 MeV energy range

Measurement of differential elastic cross section of protons from aluminum was taken at 165° degree in the2.4–4.8 Me V energy range. The results and measured energy resonances were compared with reported measurements.These data will improve the reliability of backscattering analysis of Al with protons in this energy region.     

Total cross sections for electron scattering from CH3OH and CH3CH2OH molecules in the energy range from 10 to 1000 eV

At low energy range, the additivity rule cannot give good total electron scattering cross sections for CH₃OH (methanol) and CH₃CH₂OH (ethanol) molecules. This is because electron-molecule scattering is reduced to electron-atom scattering in the additivity rule method. In this paper, considering the difference between the bound atom in the molecule and the free atom, the additivity rule has been revised. With the revised additivity rule, the total cross sections for electron scattering from CH₃OH and CH₃CH₂OH molecules over a wide energy range from 10 to 1000 eV have been calculated and compared with the available experimental and theoretical data. Better agreement is obtained. Above 500 eV, there exist no experimental data, so the present calculations can give a reference for further experimental studies.     

Excitation, ionization, and electron capture cross sections for collisions of Li with ground state and excited hydrogen atoms

Using the available experimental and theoretical data, as well as the established cross section scaling relationships, a comprehensive cross section database for excitation, ionization and electron capture in collisions of Li³⁺ ions with ground state and excited hydrogen atoms has been generated. The critically assessed cross sections are represented by analytic fit functions that have the correct asymptotic behavior both at low and high collision energies. The derived cross sections are also presented in graphical form.     

Ionization of molecules by electron impact: Differential and total cross sections

The first Born approximation is applied to calculate differential and total ionization cross sections of a set of small molecules, namely, HF, H₂O, NH₃ and CH₄ by electron impact. The molecular targets are described by single center molecular orbitals consisting of linear combinations of atomic orbitals (MO-LCAO). First, we have considered electron momentum spectroscopy experiments to check the accuracy of the wave functions. The triply, doubly, singly differential and total cross sections are then evaluated in a systematic way for a variety of kinematics. The results are discussed and compared with experiments.     

Momentum-transfer cross sections for electron collisions with atoms and molecules: Revision and supplement, 1977

This paper is a revision and extension of the compilation published in Atomic Data and Nuclear Data Tables14, 1 (1974). Experimental and theoretical data on momentum-transfer cross sections for electron collisions with atoms and molecules were surveyed to estimate the best values. Re-examination of the available data has been made through August 1977 to revise the recommendations in the previous paper for He, O, Ne, Ar, Hg, H₂, CO, H₂O, and CO₂. Furthermore the survey is now extended to Li and K. The best values are presented graphically as functions of the electron energy over the range from 0.01 to 10 eV.     

Measurement of Sc and V K—shell ionization cross sections by slow electron impact

Electron-induced Sc and V K-shell ionization cross sections,which are scarce have been obtained from measurement of KαX-ray emission cross sections at energies from near threshold to 25keV.The influence of substrate of thin targets on ionization cross sections has been corrected using the bipartition model of electron transprot.     

0.96-2.74MeV质子在铝上的160°散射截面测量

采用薄靶对能量0.962.74MeV质子在纯度为99.99%铝上的160非卢瑟福弹性背散射截面进行了测量。质子束由21.7MV串列加速器提供,测量仪器采用金硅面垒探测能谱仪。实验中最低能区进入卢瑟福弹性散射能区,测量结果用图表形式给出,并与以前发表的结果进行了比较。所测量数据可供从事背散射分析技术的有关人员参考。     

质子在天然硼上的非卢瑟福弹性背散射截面测量

采用相对测量法对能量为0.15-2.00MeV的质子在天然硼上的非卢瑟福弹性背散射截面(160     

A revised additivity rule for electron scattering from ethylene, propene, butene, ethane, propane and butane

Considering the difference between the bound atom in a molecule and the free atom, the original additivity rule is revised. Using the revised additivity rule, the total cross sections for electron scattering by ethylene (C₂H₄), propene (C₃H₆), butene (C₄H₈), ethane (C₂H₆), propane (C₃H₈) and butane (C₄H₁₀) are calculated over the energy range 10-1000 eV. The results of the revised additivity rule are compared with those obtained by experiments and the revised additivity rule can give better agreement with experimental values than the original additivity rule.     

Negative ions, energy loss, and electron emission during grazing scattering of fast H and He atoms from a clean and oxidized NiAl(1 1 0) surface

Negative ion fractions, projectile energy loss, and the emission of electrons is studied for grazing scattering of hydrogen and helium atoms/ions from a clean and oxidized NiAl(1 1 0) surface. Making use of translation energy spectroscopy and the coincident detection of the number of emitted electrons we have studied the electronic interaction mechanisms for the change from a clean metal target to an insulator surface via the preparation of a well defined ultrathin alumina film on top of the metal substrate. We find that already for a monolayer thick oxide film the characteristic different features of electronic processes for the surface of an insulator crystal are present.     

Proton elastic scattering cross sections of carbon,nitrogen and silicon for backscattering analysis in the energy range 0.7—2.5 MeV

Differential elastic scattering cross sections of 0.7—2.5 MeV protons for carbon, nitrogen and silicon have been determined at a scattering angle θ = 170°. Results from previous measurements near θ = 170° show large variations, of the order of 10–30% in the nonresonant regions. The purpose of the present investigations is to tabulate cross section data for backscattering analysis at a single scattering angle for many elements. Proton backscattering in the non-Rutherford energy region is more sensitive in the detection of C, N and many other light elements than other ion beam methods when a high background from the matrix is absent. Proton backscattering by using the present scattering cross sections and computer data analysis are outlined. The possible interference from other nuclear reactions is considered.     

Measurements and evaluation of the cross-section for helium elastic scattering from nitrogen

The cross-sections for the elastic scattering of alphas from natural nitrogen were measured at three laboratory scattering angles: 118°, 150° and 165° at non-Rutherford scattering energies from 2.5 to 4.0 MeV. Experimental data obtained in this work, together with all previously published data, were used for the cross-section evaluation. Model calculations with comparison and fitting to the experimental data were used for the evaluation of the cross-section. As a result of the work, the recommended cross-sections for scattering of alphas from nitrogen have been produced in the energy region of 1.6-4.6 MeV.     

Resonant mechanisms for negative ionization of secondary emitted atoms from sputtered metals

A model is presented to describe negative ionization of low energy, secondary atomic particles ejected from sputtered metal surfaces. Focus is made on the diatomic systems formed, in the collision cascade generated by the primary ion beam, between secondary emitted atoms and their nearest-neighbor substrate atoms that provide the initial impulse for ejection. Two different resonant ionization mechanisms are investigated such that a conduction electron may tunnel into the affinity orbital of the ejected atom either by direct hopping or after an intermediate transition via the affinity orbital of the substrate atom. A numerical method is outlined to calculate the negative ionization probability of secondary emitted atoms. A good agreement is found with van Der Heide’s measurements of the Cu⁻ population sputtered from a clean Cu-surface, at emission energies below 100 eV.     

A crossed photon-atom beam method for absolute measurement of total photoionization cross sections on isolated metal atoms: Measurements on Ba and Eu atoms

A crossed photon-atom beam apparatus has been constructed for absolute measurement of total photoionization cross sections of isolated and neutral metallic atoms. The main purpose is to establish the technique which can be used as widely as possible for the metallic elements. Using this apparatus, measurements on Ba and Eu atoms have been made at selected energies in their 4d giant resonance regions 110-140 eV and 140-180 eV, respectively. A monochromatized synchrotron radiation was used as a light source. The target-atom density in the interaction section was determined with accuracy of 9% using the accumulation rate of metallic atoms on a quartz crystal sensor and the average velocity of the atoms obtained by a time-of-flight method combined with a pulsed electron gun. The number of photons was determined with use of a double-ion chamber preferably. The entire systematic errors have been estimated to be 20% for Ba and 27% for Eu. The comparison of the measured cross-section values with previous experimental and theoretical results is reasonable, indicating that the crossed photon-atom beam method is fairly promising technique.