Density-density correlations within a nanosample irradiated by an XFEL pulse

Complete text of publication follows. Single molecule imaging at atomic (0.1nm) resolution is a major goal for the present and forthcoming X-ray Free Electron Lasers (LCLS, European XFEL, SCSS). The high intensity (1020 W/cm2) and the extremely short pulselength (<100fs) of the XFEL beam are needed to get a sufficiently strong scattering signal from the sample and to reduce the effect of radiation damage at the same time. However, the measured diffraction patterns are still influenced by the deterioration of the sample during pulse, so modelling and understanding of the dynamics of radiation damage is needed. Continuum approach is an effective way of modelling dynamics of 10-100 nm size samples, that can be used to investigate the changes of the diffraction pattern. However, continuum models deliver information on average quantities (e.g. average electron and ion densities), so scattering intensities derived this way may differ from the scattering intensities obtained by averaging over individual diffraction patterns. The difference depends on density-density correlation functions. Here we report on the theoretical and numerical investigation of the electron density-density correlation function in irradiated systems during single biomolecule imaging process. The suitability of applying the continuum model for image degradation studies will be discussed.