Proton irradiation of DNA nucleosides in the gas phase

International audienceThe four DNA nucleosides guanosine, adenosine, cytidine and thymidine have been produced in the gas phase by a laser thermal desorption source, and irradiated by a beam of protons with 5 keV kinetic energy. The molecular ions as well as energetic neutrals formed have been analyzed by mass spectrometry in order to shed light on the ionization and fragmentation processes triggered by proton collision. A range of 8-20 eV has been estimated for the binding energy of the electron captured by the proton. Glycosidic bond cleavage between the base and sugar has been observed with a high probability for all nucleosides, resulting in predominantly intact base ions for guanosine, adenosine, and cytidine but not for thymidine where intact sugar ions are dominant. This behavior is influenced by the ionization energies of the nucleobases (G < A < C < T), which seems to determine the localization of the charge following the initial ionization. This charge transfer process can also be inferred from the production of protonated base ions, which have a similar dependence on the base ionization potential. Other dissociation pathways have also been identified, including further fragmentation of the base and sugar moieties for thymidine and guanosine, respectively, and partial breakup of the sugar ring without glycosidic bond cleavage mainly for adenosine and cytidine. These results show that charge localization following ionization by proton irradiation is important in determining dissociation pathways of isolated nucleosides, which could in turn influence direct radiation damage in DNA

Electron Capture in Collisions of Slow Highly Charged Ions with an Atom and a Molecule: Processes and Fragmentation Dynamics

International audienceProcesses involved in slow collisions between highly charged ions (HCI) and neutral targets are presented. First, the mechanisms responsible for double electron capture are discussed. We show that, while the electron-nucleus interaction is expected to be dominant at projectile velocities of about 0.5 a.u., the electron-electron interaction plays a decisive role during the collision and gains importance when the projectile velocity decreases. This interaction has also to be invoked in the capture of core electrons by HCI. Finally, the molecular fragmentation of H2 following the impact of HCI is studied

Pompage optique de l'helium par un laser accordable pompe par diode laser : perspectives en magnetometrie

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Dynamics of triatomic molecular fragmentation (contribution of geometry)

CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Highly charged ions transmission through insulating capillaries

La dynamique de la transmission d ions lents multichargés au travers de capillaires isolants a été étudiée à l aide d un faisceau d ions Ar9+ d une énergie de 27 keV. L évolution temporelle de cette transmission dans des capillaires coniques a été mesurée pour un faisceau d une intensité de l ordre de 10 pA. Un modèle de distribution de charge en îlots est proposé pour expliquer cette évolution. Il s agit de la première utilisation de capillaires coniques dont la forme semble être la meilleure pour produire des micro-faisceaux de forte intensité. A plus haute énergie, quelques MeV/u, les processus mis en jeu lors de la transmission d ions par des capillaires de verre ont été étudiés dans le cas du 129Xe19+ à 71 MeV et du 78Kr 10+ à 26.5 MeV. Les images, annulaire pour les capillaires coniques et halo dans le cas des capillaires étirés, obtenues sur le détecteur sensible en position (PSD) sont attribuées à une diffusion aux petits angles des ions sur les parois. De plus, grâce à la structure en temps du faisceau pulsé à 10 Mhz, la perte d énergie subie par les ions lors de leur passage dans le capillaire a été déterminée par une mesure de temps de vol.For the purpose of revealing the features of the dynamic evolution of the slow highly charged ions transmission through the capillary, 27 keV Ar 9+ions were injected into individual glass capillaries. The time evolution of insulating conical shaped capillary guiding is observed in details at an injected intensity of ~10 pA and a scenario including several charge patches is introduced for explaining the dynamical evolution. This is the first report on conical capillaries which might be a good shape for high intensity micro-beams. In the MeV energy range, the experiment was performed for 71 MeV 129Xe19+ and 26.5 MeV 78Kr 10+ to reveal the physics mechanism of fast HCIs transmission through glass capillary. The obtained doughnut shape images on the PSD for the conical capillary and the halo structure for the tapered capillary are attributed to small angle Rutherford scattering. Furthermore, energy loss is revealed by time of flight spectra, taking the advantage of the 10 MHz pulsed incident beam.CAEN-BU Sciences et STAPS (141182103) / SudocSudocFranceF

Expected strong angular dependence of multi-ionization cross sections of diatomic molecules

International audienc

UN laser solide accordable pompe par diode

International audienc

Collisions of ions with insulator surfaces: charging and discharging dynamics

International audienceThe guiding of ions in keV to MeV energy range by insulator microcapillaries opens interesting perspectives such as direct injection of ions inside a living cell, formation of surface nano-structures, etc. We have studied the dynamic behaviour of charge deposition and beam deflection on insulators having well defined planar geometry when the exact number of charges implanted into the surface, as well as the time evolution of the beam deflection, can be monitored. The used materials, borosilicate, fused silica and quartz, are of interest for production of tapered microcapillaries. Depending on the temperature of the sample, surface composition and structure, charging and discharging dynamics varies by orders of magnitude, giving rise to different guiding effects in insulator microcapillaries. The charging process is compared to simple simulations in order to explain the observed behaviour

Diode pumping of LNA lasers for helium optical pumping

International audienc