Soutenance de thèse / PhD Defense – Marziyeh Salimi – 14/03/22

The overall objective of this thesis is to contribute experimentally determined and evaluated cross sections to a differential cross-section database for Ion Beam Analysis (IBA) that contains accurate and reliable data freely available to the user community, such as the Ion Beam Analysis Nuclear Data Library (IBANDL) database (https://www-nds.iaea.org/exfor/ibandl.htm) [1].

In the first part of the present thesis, we determined differential cross-sections of the reactions ²⁷Al(d,p&α) and benchmarked them with thick target spectra derived from pure aluminum in two independent laboratories. The differential cross section of ²⁷Al(d,p&α) reactions was determined between 1.4 and 2 MeV at scattering angles of 165°, 150°, and 135° in the VDGT laboratory in Tehran (Iran), as well as measuring them again, including target preparation, at a scattering angle of 150° with independent equipment at INSP in Paris (France). We found close agreement between these two experimental measurements in two different laboratories at 150°. There is no nuclear reaction model that can be adjusted to represent these cross sections since the compound nucleus has a level structure that cannot be treated with current models. We proposed a fitted Fourier series function to represent the evaluated data to define the Al-cross sections. The evaluated differential cross sections have been benchmarked and validated using thick target charged particle spectra obtained using incident deuteron beams of energies between 1.6 and 2 MeV at both laboratories. The validation was performed by fitting deuteron-induced particle spectra obtained from a high purity bulk Al target with SIMNRA, and the thick target spectra are reproduced, allowing the recommendation of the use of these cross sections for NRA.

      In the second part of the present thesis, the elastic proton scattering cross sections on ¹⁷O were measured for the first time at the SAFIR platform at INSP in Paris. Thin films of ¹⁷O were prepared by thermal oxidation of Si at 1100 °C under ¹⁷O₂. The physical thickness of the silica was determined by ellipsometry and the atomic thickness by RBS with an uncertainty of 3%. The small quantities of ¹⁸O and ¹⁶O, present as impurities in the highly enriched ¹⁷O₂ gas used to grow these films, were determined by the established NRA techniques using the ¹⁸O(p,α)¹⁵N and ¹⁶O(d, p₁)¹⁷O nuclear reactions.

We determined the yield of elastically scattered protons using the corresponding peak in the Elastic Backscattering spectra (EBS) spectra; however, this peak sits on the large continuous signal from the silicon substrate. The Si signal was significantly suppressed by aligning the incident beam with the (100) axis of the single crystal silicon by ion channeling. The solid angle of the detector, placed at a scattering angle of 165°, was determined by elastic scattering measurements of 2 MeV alpha particles on a reference sample of Bi implanted in Si. The measured ¹⁷O(p,p) cross section, with a systematic uncertainty of about 14%, consists of several resonant structures superimposed on a smoothly varying component increasing ranging from about 1.2 times the Rutherford cross section at 600 keV to about 3 times Rutherford at 2 MeV. A resonance at 1230 keV shows promise for EBS depth profiling, especially at large backscattering angles.