Recoil Cross Section Research Articles

Quantitative hydrogen analysis by simultaneous detection of 1H( 19F, αγ) 16O at 6.46 MeV and 19F-ERDA

A new technique is presented for determining directly the hydrogen concentration near the surface region of solids. We have utilized the detection of α-particles, instead of γ-rays, from the 6.46 MeV 19F resonance nuclear reaction (RNRA) and the elastic recoil detection (ERDA) of hydrogen induced by incident 19F ions simultaneously, to obtain the depth profile of hydrogen in solids. Advantages of this technique include: (1) RNRA can complement the poor depth resolution of ERDA, (2) ERDA can complement the larger time consumption of RNRA, (3) the recoil cross section for hydrogen of 19F-ERDA is in agreement with that of Rutherford scattering.

Measurements of the differential cross sections for recoil tritons in 4He− 3T scattering at energies between 0.5 and 2.5 MeV

Differential cross-sections for recoil detection of tritons from elastic scattering of α-particles on tritium were measured at forward recoil angles from 10° and 40° and over incident 4He energies ranging from 0.5 to 2.5 MeV. Thin solid state targets consisted of about 10 16T at. cm 2 either absorbed in a thin film of titanium or implanted at low energy in the matrix of amorphous silicon. The recoil yields were normalized against the yields of the T(d, α)n reaction measured on the same targets. It is found that the cross sections obtained are considerably enhanced as compared to the Rutherford recoil cross section, what can be attributed to the combined effect of Coulomb and nuclear potentials and formation of compound 7Li nuclei. The applications of the elastic recoil detection as a means for depth profiling of tritium in materials are briefly considered. The measured dependence of the triton recoil cross section on the incident energy of 4He + ions allows profiling the concentration of tritium across a range ∼ l μm below the surface of solids.

Primary ion dependence of LiF direct recoil intensities and ion fractions

Time-of-flight (TOF) spectra of the scattered and recoiled particles resulting from 1–10 keV He+, Ne+, Ar+, Kr+, and Xe+ ions impingent on surfaces of LiF thin films have been obtained. Measurements of directly recoiled (DR) neutrals plus ions and neutrals alone are used to calculate positive and negative ion fractions Y+,− from DR events. The oppositely charged ion fractions have a distinctly different behavior as a function of kinetic energy. The Y+ values exhibit a threshold at low energy followed by a plateau region at higher energy while the Y− values are maximum in the low energy region followed by a decreasing yield as energy increases. The energy dependence of Y+,− is interpreted in terms of the recently developed model [J. Chem. Phys. 85, 3615 (1986)] for electronic charge exchange in keV ion/surface collisions which considers electron promotions in the close atomic encounter and resonant and Auger transitions along the outgoing trajectory. The ionization potential of the primary ion relative to the energy levels of the target atom is shown to have a large influence on charge exchange in the close encounter. The ratio of direct recoil to scattering particle flux increases by a factor of >102 from He to Xe; scattering and recoil cross sections are used to model this process.

Hydrogen and deuterium measurements by elastic recoil detection using alpha particles

This paper presents recoil cross sections for both H and D for alpha particle bombardment in the energy range of 1.6 to 3.4 MeV. For hydrogen and deuterium, a non-Rutherford cross-section was found. For deuterium, a resonance at 2.15 MeV with fwhm of 75 keV was obtained. Calculations were carried out to find the geometrical arrangement where the maximum information concerning the probing depth can be obtained in the energy range of 1–10 MeV. In contrast to the generally accepted 30° scattering angle, another configuration is suggested.

Methoxylation of magnesium studied by direct recoil spectroscopy, SIMS and XPS: Calibration of relative surface hydrogen concentration

Chemisorption of methanol on polycrystalline magnesium is studied by time-of-flight analysis of directly recoiled (DR) surface atoms, angular resolved X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). The combined measurements show that decomposition occurs to form ∼ 0.14 monolayers of surface hydroxide at methanol exposures < 4 L. High exposures result in molecular chemisorption to form a single methoxide overlayer. The DR results reveal that the C and H of the methyl group are the outermost atoms on the saturated surface. Analysis of DR intensities allows calibration of the relative signals and comparison with calculated recoil cross sections. The methoxide/Mg system provides a standard for surface hydrogen concentrations by the direct recoil technique.

Depth resolution and recoil cross section for analyzing hydrogen in solids using elastic recoil detection with 4He beam

Two aspects of the elastic recoil detection technique for analyzing H and D are described; i) experimental factors which effectively limit the depth resolution in Al film, and ii) determination of the recoil cross section for H( 4He, 4He)H and D( 4He, 4He)D reactions in the range of 1.5–3.0 MeV energy of 4He. Both experimental and theoretical estimates of the depth resolution are presented and are in good agreement each other. The theoretical estimate therefore provides a reliable guide to find optimum resolution conditions. The recoil cross section for H is more than double the theoretical Rutherford scattering value and that for D becomes greater than 30 times Rutherford near the resonance energy of 2.1 MeV 4He.

TOF spectra of direct recoils: I. Chemisorption of O 2, H 2O, and CH 2OH on magnesium

Time-of-flight (TOF) analysis of directly recoiled surface atoms (neutrals and ions) produced by pulsed Ar + ion irradiation has been used to monitor chemisorption of O 2, H 2O, and CH 3OH on polycrystalline magnesium. The intensities of the H, C, O, and Mg direct recoils are obtained as a function of gas exposure dose. The reaction with O 2 is fast, with saturation occurring at ∼ 10 L (1 L = 10 −6 Torr s), and following either a one- or a two-site adsorption model while the H 2O and CH 3OH reaction are slower, with saturation occurring at ∼ 20 L, and following a nucleation and growth expression. The hydrogen direct recoil intensitiy has been calibrated to the amount of hydrogen on a methoxylated surface. This calibration allows determination of H coverages during the O 2 and H 2O reactions and shows a surface stoichiometry consistent with Mg(OH) 2 for the water reaction. The analysis indicates that the oxygen forms an oxide at sites that are within the outermost Mg layer while the H 2O and CH 3OH form hydroxide and methoxide layers which are above the outermost Mg layer. Scattering and direct recoil cross-sections and shadow cones are calculated by means of a program which uses the Molière approximation to the interaction potential for single binary encounters.

Helium-induced hydrogen recoil analysis for metallurgical applications

A number of studies of hydrogen in metals require special capabilities not easily met by the usual nuclear reaction analysis techniques (NRA). As part of a study of hydrogen redistribution in stressed metals, hydrogen concentrations had to be measured with high statistical accuracy (one percent or better) in short times (of order 10 s) and without significant ion beam effects on the sample. Our method has been to measure the energy spectrum of protons projected out of thin metal foils at 0° by 3.5–5.0 MeV 3He and 4He ions which have elastic scattering cross-sections orders of magnitude greater than Rutherford. Event rates of 2000 counts/s have been achieved with beam currents 10 nA for metal foils loaded with 10 at.% H. This technique is described and compared to the more usual NRA procedures. Its application to the study of H redistribution in stressed metals is briefly discussed. Recoil cross sections have been evaluated from known p- 4He phase shifts and tabulated for use in absolute measurements of depth profiles. These cross sections should also be useful in glancing-angle recoil geometries.

Determination of the neutron flux and energy spectrum in the low-temperature fast-neutron facility in CP-5, calculations of primary-recoil and damage-energy distributions, and comparisons with experiment

We have determined the absolute differential neutron-energy spectrum for the low-temperature fast-neutron irradiation facility in the CP-5 reactor by means of a 20-foil activation technique. This technique employs the most recent version of the SAND-II computer code, which iteratively unfolds the neutron spectrum by fitting the foil activities. A Monte Carlo routine was also employed to calculate standard-deviation errors in each neutron-energy group. Using this differential neutron spectrum we have calculated, for numerous elements, total recoil cross sections, detailed primary-recoil group distributions, total damage-energy cross sections, damage-energy distributions, and an error analysis based on the uncertainties in the neutron spectrum. The significance of this information with respect to the interpretation of various neutron radiation-damage experiments, including sputtering, disordering of ordered alloys, and changes in critical current of A-15 compound superconductors is discussed. A detailed comparison is made among initial resistivity-damage rates for five widely different (well characterized) neutron sources, fission fragments, and heavy ions.

Electropion production inHe3determined by measuring the triton recoil cross section

The $^{3}\mathrm{He}(e, t){\ensuremath{\pi}}^{+}$, ${e}^{\ensuremath{'}}$ cross section has been measured as a function of incident electron energy, triton recoil energy, and angle. The experiment corresponds to excitation energies near 20 MeV above pion threshold. Comparison is made with a theory including all partial waves using Gaussian and Irving-Gunn ground states for $^{3}\mathrm{He}$. The forward peaking approximation is also discussed.NUCLEAR REACTIONS $^{3}\mathrm{He}(e, t){\ensuremath{\pi}}^{+}$, ${e}^{\ensuremath{'}}$, measured $\ensuremath{\sigma}({E}_{t}, {\ensuremath{\theta}}_{t}, {E}_{0})$ compared with electropion production theory.