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Happy phasing with electronic radiation damage at high x-ray intensity
Sang-Kil Son8th International Workshop on X-ray Radiation Damage to Biological Crystalline Samples
(Hamburg, Germany, April 10-12, 2014) [invited talk]
The multiwavelength anomalous diffraction (MAD) method is used to determine phase information in x-ray crystallography by employing anomalous scattering from heavy atoms. X-ray free-electron lasers (XFELs) show promise for revealing molecular structure using femtosecond x-ray nanocrystallography, but the associated phase problem remains largely unsolved. Because of the extremely high intensity of XFELs, samples experience severe and unavoidable electronic radiation damage, especially to heavy atoms, which hinders direct implementation of MAD with XFELs. We propose a high-intensity version of the MAD phasing method. The proposed method requires the ability to describe the dynamical behavior of heavy atoms at high x-ray intensity. In this talk, I will discuss a theoretical model of electronic radiation damage dynamics during intense x-ray pulses and present the XATOM toolkit to simulate detailed x-ray ionization and relaxation dynamics of heavy atoms. I will demonstrate the existence, in spite of the high degree of ionization, of a Karle-Hendrickson-type equation in the high-intensity regime. Then I will discuss that novel high-intensity phasing methods, because of the high degree of ionization, are achievable in femtosecond x-ray nanocrystallography with XFELs.
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