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Phasing with electronic radiation damage at high x-ray intensity
Sang-Kil SonBioXFEL STC 2nd Annual International Conference
(Ponce, Puerto Rico, January 14-16, 2015) [invited talk]
X-ray free-electron lasers (XFELs) show promise for revealing bio-macromolecular structure using serial femtosecond crystallography (SFX), but the associated phase problem remains largely unsolved. Many of ab initio phasing methods with synchrotron radiation employ anomalous scattering from heavy atoms, for example, multiwavelength anomalous diffraction (MAD). 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 those phasing techniques with XFELs. In this talk, I will present a theoretical model of electronic radiation damage dynamics during intense x-ray pulses. The XATOM toolkit is used to simulate electronic radiation damage dynamics – detailed x-ray ionization and relaxation dynamics – of heavy atoms. Then, I will discuss how to turn x-ray multiple ionization at high intensity into an advantage for SFX. It will be demonstrated that a key equation for MAD in the high-intensity regime exists in spite of the high degree of ionization and that novel high-intensity phasing methods are achievable utilizing the high degree of ionization. I will also discuss challenges towards new high-intensity phasing methods in SFX experiments.
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