Interaction of ion beams with water and other small molecules of

R. RIVAROLA; M.E. GALASSI; O. FOJON; C. CHAMPION; J. HANSEN; P.D. FAINSTEIN

Madrid

Conferencia; 7th International Conference on Radiation Damage in Biomolecular Systems; 2010

The study of electronic reactions produced by the impact of ion beams on molecular targets is of fundamental importance in many areas of Physics, like Plasma Physics, Astrophysics and Medical Physics. Special attention has been devoted in recent years to its application in Radiotherapy. As the biological tissue is mostly composed by water, this target has been usually employed in numerous investigations. Thus, we focus our interest on water molecules but also on other small molecules present in live matter, like O2, CO, N2, CO2 and CH4. Our theoretical analysis is performed using quantum mechanical models, in particular the continuum distorted wave-eikonal initial state (CDW-EIS, [1]) and a first-order of the Born series (FBA, [2-3]), both formulated to verify correct boundary conditions in the entry and exit channels. One active electron and multiple active electron reactions will be investigated. It must be noted that the production of radicals with oxygen excess in biological tissue irradiation has been recently attributed to multiple ionization of water [4-5]. The processes here considered are single electron capture and single and multiple electron ionization. Multiple and single differential cross sections and total cross sections are calculated and compared with existing experimental data for the different systems above mentioned. The validity of the use of the CDW-EIS and FBA approximations to describe the corresponding cross sections is investigated by contrasting with measurements. In particular, the rôle played by the representation of the molecular orbitals will be discussed for water targets in gaseous and liquid phases. Calculations of equilibrium charge state fractions will be also presented paying particular attention to their influences on the determination of total mean electronic stopping power in the different projectile energetic domains.       [1] P. D. Fainstein, V. H. Ponce and R. D. Rivarola, Phys. Rev. A 21, 287 (1988). [2] Dž. Belkiæ, R. Gayet, J. Hanssen and A. Salin, J. Phys. B 19, 2945 (1986). [3] O. Boudrioua, C. Champion, C. Dal Capello and Y. V. Popov, Phys. Rev. A 75, 022720 (2007).  [4] B. Gervais, M. Beuve, G. H. Olivera, M. E. Galassi and R. D. Rivarola, Chem. Phys. Lett. 410, 330 (2005). [5] B. Gervais, M. Beuve, G. H. Olivera and M. E. Galassi, Rad. Phys. Chem. 75, 493 (2006).