Experimental determination of cross sections for K-shell ionization by electron impact for C, O, Al, Si, and Ti

Cross sections for K-shell ionization by electron impact were determined from films of Al, Si, and Ti and their oxides deposited on carbon substrates, for incident energies between 2.5 and 25 keV. The spectral processing of the x-ray emission spectra took into account corrections due to the presence of a spontaneous oxide layer formed on the monoelemental films and to the supporting material. CarbonK-shell ionization cross sections were determined from the contribution of the substrate to the measured spectra, while for oxygen, data from the three oxide films were taken. The mass thickness of the coatings was characterized by x-ray reflectivity. The results obtained were compared with other experimental data sets, semiempirical approaches, and theoretical models

Energy deposition of H and He ion beams in hydroxyapatite films: a study with implications for ion-beam cancer therapy

Ion-beam cancer therapy is a promising technique to treat deep-seated tumors; however, for an accurate treatment planning, the energy deposition by the ions must be well known both in and human tissues. Although the energy loss of ions in water and other organic and biological materials is fairly well known, scarce information is available for the tissues (i.e., bone), for which the current stopping power information relies on the application of simple additivity rules to atomic data. Especially, more knowledge is needed for the main constituent of human bone, calcium hydroxyapatite (HAp), which constitutes 58% of its mass composition. In this work the energy loss of H and He ion beams in HAp films has been obtained experimentally. The experiments have been performed using the Rutherford backscattering technique in an energy range of 450–2000 keV for H and 400–5000 keV for He ions. These measurements are used as a benchmark for theoretical calculations (stopping power and mean excitation energy) based on the dielectric formalism together with the MELF-GOS (Mermin energy loss function-generalized oscillator strength) method to describe the electronic excitation spectrum of HAp. The stopping power calculations are in good agreement with the experiments. Even though these experimental data are obtained for low projectile energies compared with the ones used in hadron therapy, they validate the mean excitation energy obtained theoretically, which is the fundamental quantity to accurately assess energy deposition and depth-dose curves of ion beams at clinically relevant high energies. The effect of the mean excitation energy choice on the depth-dose profile is discussed on the basis of detailed simulations. Finally, implications of the present work on the energy loss of charged particles in human cortical bone are remarked.This work has been financially supported by the Spanish Ministerio de Economía y Competividad and the European Regional Development Fund (Project FIS2010-17225) and the Brazilian agency CAPES (project CAPES-MinCyT 220/12). P.d.V. thanks theConselleria d’Educació, Cultura i Esport de laGeneralitat Valenciana for its support under the VALi+d program. This research has been developed as a part of the COST Action MP 1002, Nanoscale Insights into Ion Beam Cancer Therapy

Stopping cross sections of TiO2 for H and He ions

Stopping cross sections of TiO2 films were measured for H and He ions in the energy intervals 200–1500 keV and 250–3000 keV, respectively, using the Rutherford backscattering technique. Theoretical calculations were performed by means of two versions of the dielectric formalism and a non-linear model. Good agreement is found between the present experimental data and the theoretical results at intermediate and high energies, and also with the very limited experimental information available in the literature.We thank the financial support from the Spanish Ministerio de Economía y Competitividad (Projects FPA2009-14091-C02-01 and FIS2010-17225) and the European Regional Development Fund. This work was partially supported by the following Argentinian institutions: Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT)