CONICET | Buscador de Institutos y Recursos Humanos

The role of secondary electrons, generated by the interaction of highly charged ions (HCIs) with biological tissues, towards radiation damage is of great importance in case of radiation therapy. Precise measurement of distribution of the emitted electrons is especially important in the region of the Bragg peak, since, the largest part of the ion energy is deposited at that point. Now, the total amount of water in a human body of average weight is 65% of the total body weight. Thus, it is necessary to determine accurately, the total as well as differential cross-sections for electron emission in ionization of water molecules, to understand the inelastic processes induced by highly charged ions in biological matter. However, the existing studies are limited to electrons, protons, alpha-particles and C6+ ions as projectiles. In the present case, we have measured the double differential cross sections (DDCS) for electron emission in ionization of H2O molecule under the impact of fast (energy: 48-72 MeV) O8+ ions. The data were collected between 1-600 eV, over the angular range of 200-1500, by using an electrostatic hemispherical analyzer. The single differential cross sections (SDCS) and the total cross sections have also been obtained. The DDCS spectra are compared with both the prior & the post version of the continuum distorted wave-eikonalinitial state (CDW-EIS) model. An excellent overall agreement has been found between the data and the theory. However, the prior form of the model is found to provide a better understanding of the data compared to the post version [5]. The measured single differential cross-sections (SDCSs) exhibit good agreement with the present theoretical models as well as with the semi-empirical model proposed by Rudd. Finally, the total ionization cross sections are compared with the existing TCS values for ionization of water molecules under impact of different other heavy ions to provide a simple scaling law involving projectile charge state and velocity. This scaling procedure could therefore be used for modeling the highly charged ion induced radiation damage in living tissues. In addition, the angular asymmetry parameter for H2O under impact of different highly charged ions has been compared with that of pure atomic target, such as He as well as diatomic syatem, such as O2. A different behaviour in case of H2O has been observed, which is not understood in terms of ab-initio model calculations. Details will be presented.