W. H. Bragg Lecture 2011

Henry Chapman, 2011 W.H. Bragg Lecture Speaker

Diffraction before destruction: imaging molecules and viruses using X-ray pulses
Presented by Professor Henry Chapman
Center for Free-Electron Laser Science, DESY, Hamburg, Germany

Wednesday 26 October at 16:30 in the Harrie Massey Lecture Theatre, University College London, followed by light refreshments in E3/E7, Physics.


X-ray free-electron lasers (FELs) are very large and expensive machines that produce the briefest and most intense flashes of X-rays.  The X-ray beam at the world's first hard X-ray FEL is so intense that it melts a hole through 3 mm of stainless steel in under a second*.   Yet we apply this beam to elucidate the molecular structure of proteins and obtain images of virus particles, which are certainly more delicate than steel.  In fact, these objects are completely vaporised in the beam, and we overcome the problem of this radiation damage by using the short X-ray pulses to outrun the explosion.  Indeed, we have shown that we obtain atomic-resolution information with pulses of 30 fs or shorter.  This "diffraction before destruction" technique allows us to determine the molecular structures of proteins that cannot be grown into large enough crystals or are too radiation sensitive for conventional X-ray crystallography.  We aim to push this technique to smaller and smaller samples--all the way down to the single molecule.

*Results of an unintended experiment.

About the W.H. Bragg Lecture

In 2004 UCL's Department of Physics and Astronomy decided to establish a series of annual lectures celebrating major advances in condensed matter physics. The series was named after William Henry Bragg, who was the Head of Department from 1915 to 1923. X-ray diffraction analysis of crystal structures began with W. H. Bragg’s instrumentation and insight, and with the availability of synchrotron sources it has developed into an important tool in modern biology.