A mini scanning device for profiling charged beams

International audienceIn this article we present the development of a mini scanner device to characterize the full transverse spatial density of a charged particle beam using computed tomography. The profiler consists of a wire mounted on a linear translator that can rotate around the beam. Tests were performed on a millimeter electron beam with 200 eV energy and 100 nA intensity, which allowed us to control and monitor both beam focusing and deflection

Specific cationic emission of cisplatin following ionization by swift protons

We have investigated collision-induced ionization and fragmentation by 100 keV protons of the radio sensitizing molecule cisplatin, which is used in cancer treatments. A large emission of HCl+ and NH\hbox{$_{\mathrm{2}}^{\mathrm{+}}$} is observed, but surprisingly, no cationic fragments containing platinum are detected, in contrast to ionization-dissociation induced by electronic collision. Theoretical investigations show that the ionization processes take place on platinum and on chlorine atoms. We propose new ionization potentials for cisplatin. Dissociation limits corresponding to the measured fragmentation mass spectrum have been evaluated and the theoretical results show that the non-observed cationic fragments containing platinum are mostly associated with low dissociation energies. We have also investigated the reaction path for the hydrogen transfer from the NH3 group to the Cl atom, as well as the corresponding dissociation limits from this tautomeric form. Here again the cations containing platinum correspond to lower dissociation limits. Thus, the experimental results suggest that excited states, probably formed via inner-shell ionization of the platinum atom of the molecule, correlated to higher dissociation limits are favored

Dissociation of polycyclic aromatic hydrocarbons at high energy: MD/DFTB simulations versus collision experiments: Fragmentation paths, energy distribution and internal conversion : test on the pyrene cation.

International audienceThe whole process following collisions of polycyclic aromatic hydrocarbons (PAHs) with high energetic protons is modeled and compared to the experimental mass spectrum, allowing to propose a coherent scenario. Fragmentation of cationic pyrene C 16 H + 10 is extensively studied by molecular dynamics simulations obtained by computing the electronic structure at the Self-Consistent-Charge Density Functional based Tight Binding (MD/SCC-DFTB) on-the-fly. An atomic model is used to quantify the energy transfered to the target after proton impact, and assuming fast internal conversion for the produced cations. From this model, after ionisation, the molecules show a broad distribution of internal energy with a rough exponential decrease. This distribution is used as an input for further extensive MD/SCC-DFTB simulations. The good agreement between experimental and theoretical spectra globally validates the SCC-DFTB potential, the wide distribution of fragments corresponding to statistical dissociation. The scenario for both the internal energy deposited distribution and the fast internal conversion assumption is validated. Using these assumptions, dissociation is shown to occur within a few hundreds of picoseconds. Moreover, adjusting the experimental mass spectrum with the theoretical spectra obtained for the various internal energies nicely returns the distribution modeled from the atomic contributions, reinforcing the coherence of the global approach. This study lays the foundations for further synergistic theoretical and experimental studies that will be devoted to other PAHs and prebiotic molecules of astrophysical interest