Electron DDCS in ionization of H2O by 72 MeV O8+ ions: comparison with CDW-EIS post and prior forms

S. NANDI; S. BISWAS; A. KHAN; A. N. AGNIHOTRI; S. KASTHURIRANGAN; J. M. MONTI; C. A. TACHINO; R. D. RIVAROLA; D. MISRA; L. C. TRIBEDI

Lanzhou

Conferencia; XXIIIV International Conference on Photonic, Electronic and Atomic Collisions; 2013

In recent years, there has been a significant development in the field of hadron therapy using both protons as well as highly charged light (Z<10) ions. The total amount of water in a human body is around 57% of the total body weight. Hence it is extremely necessary to determine accurately the total as well as differential cross-sections for ionization of water molecules in order to understand the inelastic processes induced by highly charged ions in biological tissues. However, measurements of absolute electron DDCS for ionization of H2O molecules are limited to protons [1,2], alpha particles [3], electrons [4] and fast C6+ ions [5], as the projectiles. Here we measure the absolute DDCS for electron emission from H2O, under the impact of 72-MeV O8+ ions obtained from the 14 MV tandem Pelletron accelerator at Mumbai. The experimental set-up consists of a high vacuum chamber equipped with a motorized turn table and an electrostatic hemispherical analyzer for measuring the angular as well as the energy distribution of the ejected electrons [6]. The scattering chamber was flooded with H2O vapor at a pressure around 0.15 mTorr. The DDCS values were then measured over an energy range of 1 eV to 600 eV and an angular range of 20° to 150°. A representative spectrum of the DDCS has been shown in Figure 1, which displays the continuum as well as the oxygen K-LL Auger peak. The experimental data have been compared extensively with the continuum distorted wave-eikonal initial state (CDW-EIS) calculations for both the prior as well as the post form of the scattering matrix [7]. In general, there has been a qualitative agreement between the experimental DDCS values and those from the CDW-EIS (both post and prior) model. However, a better quantitative agreement has been found for the prior version as compared to the post version. This can be attributed [8] to the fact that, the post form neglects perturbative potentials describing the short range part of the electron dynamic screening. The total ionization cross-section, as obtained from the experiment, over an energy range of 1-400 eV, is within 3% of that obtained from the theoretival calculations. Details will be presented.References[1] M Bolorizadeh et al. 1986 Phys. Rev. A 33, 888.[2] H Lüdde et al. 2009 Phys. Rev. A 80, 060702(R).[3] D Ohsawa et al. 2005 Phys. Rev. A 72, 062710.[4] M Bolorizadeh et al. 1986 Phys. Rev. A 33, 882.[5] C Dal Capello et al. 2009 Nucl. Ins. Meth. Phys. Res.  267, 157.[6] S Nandi et al. 2012 Phys. Rev. A 85, 062705.[7] M Ciappina et al. 2006 J. Phys. B 39, 1091.[8] J Monti et al. 2010 J. Phys. B 43, 205203.