[en] We study theoretically and experimentally the population dynamics of the internal state of 60 MeV/u Kr³⁵⁺ ions traversing amorphous carbon foils. A quantum transport theory is developed that incorporates the state mixing induced by the wake field of the ion as well as all the coherences generated by the collisional and radiative redistribution of states. We show that the internal state of the ion is sensitive to collisional coherences and the wake field. The results of the full simulations are found to be in good agreement with experimental data

[en] In this paper the swift heavy ion interactions with condensed matter are studied from the point of view of the modifications induced in the electronic subsystem of the target. A Monte Carlo method is used to describe event by event the interactions of the projectile with the target electrons as well as the evolution of the electronic subsystem. The validity of the method and the results are discussed. This detailed picture of the excited target could be used for further explanations and calculations of the damage creation by electronic excitation. We have focused our attention on two materials whose electronic properties are different: graphite and quartz. For both materials a quantitative analysis of the energy deposition mechanism is given. ((orig.))

[en] A complete experimental study of the production and transport of long-lifetime excited states has been done for Ar¹⁸⁺ on solid C targets, at a velocity of 23 a.u., and for a range of thickness allowing us to vary the transport conditions from single collision to equilibrium (3.5 to 201 μg/cm²). A systematic determination of Ar¹⁷⁺ Rydberg l- and 2s-state populations has been performed using the x-ray spectroscopy technique. Results are compared with predictions of different transport simulations (developed on either a quantum or a classical phase space), which take into account multiple collisions and the strong polarization induced by the incoming ion (the wakefield). Using the continuum distorted-wave approximation for modeling the initial capture process, very good agreement is found between experimental Rydberg-state populations and theoretical approaches limited to the effect of multiple collisions. On the contrary, the transport of the metastable 2s state exhibits strong sensitivity to Stark mixing induced by the wakefield. The limitation of each theoretical approach is discussed with respect to the different experimental observables

[en] The ideal picture of a near-perfect 3D microscope often presented regarding Atom Probe Tomography faces several issues. These issues degrade the metrological performance of the instrument and find their roots in the phenomena acting at the atomic to the mesoscopic level in the vicinity of the surface of a field emitter. From the field evaporation process at the atomic scale, to the macroscopic scale of the instrument, the path to model the imaging process and to develop more accurate and reliable reconstruction algorithms is not a single lane road. This paper focused on the numerical methods used to understand, treat, and potentially heal imaging issues commonly affecting the data in atom probe experiments. A lot of room for improvement exists in solving accuracy problems observed in complex materials by means of purely electrostatic models describing the image formation in a classical approach. Looking at the sample at the atomic scale, the phenomena perturbing the imaging process are subtle. An examination of atomic scale modifications of the sample surface in the presence of a high surface electric field is therefore mandatory. Atomic scale molecular dynamic models integrating the influence of the high surface electric are being developed with this aim. It is also demonstrated that the complex behavior of atoms and molecules in high fields, and consequences on collected data, can be understood through the use of accurate ab-initio models modified to include the impact of the extreme surface electric field.

[en] We briefly summarize the results of numerous experiments performed at GANIL aimed at measuring electron yields and doubly differential yields (energy or velocity spectra at different ejection angles, angular distributions). These studies, supported by theoretical investigations and numerical simulations, contributed decisively to our understanding of the very first step in energy deposition in matter, i.e. ionization and subsequent electron transport through condensed matter. The emitted electron spectrum contains a rich variety of features including binary encounter electrons (BEE), convoy electrons (CE), Auger electrons (AE) and the low-energy peak of “secondary” electrons (SE). (paper)

[en] We have investigated the production of free radicals induced by swift ions during the radiolysis of oxygenated water and analyzed the underlying mechanisms in detail. To this aim, we simulated, by Monte-Carlo, the irradiation of water by projectiles with LET values ranging from 1 to 300 keV/μm for a partial pressure of oxygen in air from 0 to 750 mmHg, and for times up to 10 μs after ion impact. For low-LET radiation, we observed an increase in production of (HO_2"· + O_2"·"−) with oxygen pressure and a saturation. At 1 μs, the saturation occurred at a pressure of 20–30 mmHg and the maximal yield amounted to 0.3 μmol L"−"1 per Gray. For the same conditions, we observed similar trends for high-LET ions, but we observed a significant reduction in the yield values and an attenuation of the saturation behavior. By underlining similarities between the yield of (HO_2"· + O_2"·"−) and the oxygen effect observed in radiobiology, we discuss the role of (HO_2"· + O_2"·"−) in oxygen effect and suggest a general mechanism for this phenomenon.

[en] The population dynamics of the internal state of 60 MeV/u Kr³⁵⁺ ions traversing amorphous carbon foils is studied theoretically and experimentally. This system is of particular interest as the times scales for collisional distribution, mixing due to the wake field, and radiative processes are comparable to each other. A transport theory based on a quantum-trajectory Monte Carlo method is developed, which treats the collisional and radiative redistribution of states on the same footing. The simulations exhibit clear signatures for the interplay between radiative decay and collisional mixing. Good agreement with experimental data is found

[en] The description of the biological effects of ionizing radiation requires a good knowledge of the dose deposition processes at both the cellular and molecular scales. However, experimental studies on the energy deposition specificity of sub-keV electrons, produced by most radiations, including high-energy photons and heavy ions, are scarce. Soft X-rays (0.2-2 keV) are here used to probe the physical and physico-chemical events occurring upon exposure of liquid water to sub-keV electrons. Liquid water samples were irradiated with a monochromatic photon beam at the SOLEIL synchrotron. Hydroxyl radical quantification was conducted through HO^. scavenging using benzoate to form fluorescent hydroxybenzoate. The yields of HO^. radicals exhibit a minimum around 1.5 keV, in good agreement with indirect observation. Moreover, they are relatively independent of the benzoate concentration in the range investigated, which corresponds to scavenging times of 170 ns to 170 ps. These results provide evidence that sub-keV electrons behave as high linear energy transfer particles, since they are able to deposit tens to hundreds of electron volts in nanometric volumes. (authors)

[en] Highlights: • We calculated radical production around gold/water nanoparticle (GNP/WNP) in water. • Calculations were performed for single keV photon absorption. • In the micrometer range, radicals are overproduced by GNP compared to WNP. • In the nanometer range, radicals are overproduced by small GNP compared to WNP due to Auger electrons. • In the nanometer range, radical production is comparable for large NP. For the past two decades, gold nanoparticles (GNPs) have been investigated as a radiosensitizing agent for radiation therapy. Many theoretical studies have shown that GNPs increase the dose deposition for keV photon irradiation, both at macro and nano-scales, due to a high photon-gold interaction probability. We studied by Monte Carlo simulations the production of radiolysis chemical products (${}_{•}\text{O}\text{H}$ and ${\text{H}}_2{\text{O}}_2$) following an ionization event induced by a 20–90 keV photon in a nanoparticle (NP). We focused here on the primary chemical processes occurring around nanoparticles. In the micrometer range, we obtained an excess of chemical species following GNP ionization, as compared to a reference water nanoparticle (WNP) ionization. This difference came from the dominant processes of photon interaction, i.e., Compton for water and photoelectric for gold, which are characterized by different emitted-electron energy spectra. The overproduction of chemical species could be up to 5 times higher for GNP, depending on the photon energy. The mean concentration of chemical species within 100 nm is higher for GNPs compared to WNPs due to Auger electrons when the nanoparticle radius was equal to 5 nm. On the contrary, it was quite comparable when the nanoparticle radius was equal to 50 nm. This reveals that gold Auger-electrons do not necessarily induce a significant boost of chemical species in the vicinity of GNP, as compared to WNP. However, the chance of GNP ionization to occur is larger, due to higher photon-gold interaction probability than that of water, and could result, especially for large GNPs, in accumulation of oxidative stress in its vicinity.