Clusters in the XFEL beam

Among the future X-ray sources linac-based X-ray free electron lasers are close to realization. They will produce extremely short (<100 fs) and intense hard X-ray pulses (similar to 10(12) photon/pulse). The unique features of this beam will allow the study of the atomic structure and the different physical and chemical processes in solids at a level which is not accessible today. However, to understand the experimental results a detailed picture of what happens during the burst in the sample is necessary. In several suggested applications, small samples containing only 10(3)-10(6) atoms are the possible candidates. In order to have an understanding about the atomic motions, we performed model calculations on the dynamics of particles of a cluster in an intense hard X-ray pulse. The movement of the particles was followed by non-relativistic classical dynamics. The main processes: photo-absorption, Auger process, inelastic and elastic scattering of electrons were taken into account by their respective cross sections. Here, we report our findings on clusters containing various elements. The results show that the clusters disintegrate via Coulomb explosion, similar to small clusters in intense laser beam. However, the dynamics of the explosion is significantly different. We investigate the effect of cluster size, pulse length,atom density and composition on the explosion. We discuss the consequences of our results to single-molecule imaging by the free-electron laser pulses, recently proposed by Neutze et al. [R. Neutze, R. Wouts, D. Spoel, E. Weckert, J. Hajdu, Nature, 406 (2000) 752]. The critical evaluation of these results gives guidelines and sets important limits on experimental conditions for future experiments aiming for single-molecule structure solution. (c) 2005 Elsevier B.V. All rights reserved.