  Structural studies of biological macromolecules are severely limited by
radiation damage. Traditional crystallography curbs the effects of damage by
spreading damage over many copies of the molecule of interest. X-ray lasers,
such as the recently built LINAC Coherent Light Source (LCLS), offer an
additional opportunity for limiting damage by out-running damage processes with
ultrashort and very intense X-ray pulses. Such pulses may allow the imaging of
single molecules, clusters or nanoparticles, but coherent flash imaging will
also open up new avenues for structural studies on nano- and micro-crystalline
substances. This paper addresses the theoretical potentials and limitations of
nanocrystallography with extremely intense coherent X-ray pulses. We use urea
nanocrystals as a model for generic biological substances and simulate primary
and secondary ionization dynamics in the crystalline sample. Our results
establish conditions for ultrafast nanocrystallography diffraction experiments
as a function of fluence and pulse duration.
