Low energy ion backscattering spectrometry of multi-layer targets. - Energy loss and straggling of H and He ions of keV energies in Si and C

SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Calculation of energy-loss straggling of C, Al, Si, and Cu for fast H, He, and Li ions

We present theoretical calculations of the energy-loss straggling of C, Al, Si, and Cu targets for H, He, and Li ions in the range of intermediate to high energies (0.01–10 MeV∕u). These calculations have been done by employing the dielectric formalism and by considering the different equilibrium charge states of the swift ion inside the solid as a function of its energy. Two different models are used: the Mermin energy-loss functions combined with generalized oscillator strengths (MELF-GOS) and the shellwise application of the local plasma approximation (SLPA). The MELF-GOS describes the target outer-electron excitations through a fitting to experimental data in the optical limit, employing a linear combination of Mermin-type energy-loss functions; the excitations of the inner-shell electrons are taken into account by means of generalized oscillator strengths. The SLPA employs a free-electron-gas model for the target valence electrons and the local density approximation for each shell of target electrons separately by using Hartree-Fock atomic wave functions. The results of the energy-loss straggling obtained by the two independent models show good agreement with the available experimental data. The calculated energy-loss straggling tends at high energies to the Bohr value and takes values below it at intermediate energies. The Bethe-Livingston shoulder (or overshooting) at intermediate energies does not appear in the present calculations. We find that the energy-loss straggling normalized to ZP2 is almost independent of the ion atomic number ZP; therefore, the results for H, He, and Li projectiles in each target can be approximated by a universal curve at high energies.This work was supported by the Spanish Ministerio de Educación y Ciencia (Projects Nos. BFM2003-04457-C02-01 and BFM2003-04457-C02-02), by the Universidad de Buenos Aires (Project UBACyT), the Argentinian Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), and the Agencia Nacional de Promoción Científica y Tecnológica of Argentina (ANPCyT). S.H.A. thanks Fundación Cajamurcia for a postdoctoral grant

An Association Study between Hypoxia Inducible Factor-1alpha (HIF-1 alpha) Polymorphisms and Osteonecrosis

Bone hypoxia resulting from impaired blood flow is the final pathway for the development of osteonecrosis (ON). The aim of this study was to evaluate if HIF-1 alpha, the major transcription factor triggered by hypoxia, is genetically implicated in susceptibility to ON. For this we analyzed frequencies of three known HIF-1 alpha polymorphisms: one in exon 2 (C111A) and two in exon 12 (C1772T and G1790A) and their association with ON in a Greek population. Genotype analysis was performed using PCR-RFLP and rare alleles were further confirmed with sequencing. We found that genotype and allele frequency of C1772T and G1790A SNP of HIF-1 alpha (SNPs found in our cohort) were not significantly different in ON patients compared to control patients. Furthermore these SNPs could not be associated with the different subgroups of ON. At the protein level we observed that the corresponding mutations (P582S and A588T, respectively) are not significant for protein function since the activity, expression and localization of the mutant proteins is practically indistinguishable from wt in HEK293 and Saos-2 cells. These results suggest that these missense mutations in the HIF-1 alpha gene are not important for the risk of developing ON

Interaction of low energy protons, deuterons,

We have performed measurements of energy-angle distributions for low energy (E ≲ 10 keV) hydrogen ions transmitted through thin amorphous carbon foils. The applicability of standard potentials for the description of the multiple scattering is tested by making comparisons of the experimental results with theoretical calculations using the model of Sigmund and Winterbon on a broad angular scale. The angular dependence of the energy loss for protons and deuterons is analyzed using the three-components model of Famá et al., that separately considers the contribution of elastic and inelastic mechanisms and the roughness effect. Additionally, the velocity dependence of the stopping power and the possible existence of isotopic and molecular effects in the energy loss is investigated by measurements with H+, D+, \hbox{${\rm H}_2^+$} and \hbox{${\rm D}_2^+$} beams of velocities between 0.15 and 0.6 a.u