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Measuring energy-dependent photoelectron escape in microcrystals

DOI: 10.1107/S2052252519016178 DOI Help

Authors: Selina L. S. Storm (Diamond Light Source) , Adam D. Crawshaw (Diamond Light Source) , Nicholas E. Devenish (Diamond Light Source) , Rachel Bolton (Diamond Light Source; University of Southampton Centre for Biological Sciences) , David R. Hall (Diamond Light Source) , Ivo Tews (University of Southampton) , Gwyndaf Evans (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Iucrj , VOL 7 , PAGES 129 - 135

State: Published (Approved)
Published: January 2020

Open Access Open Access

Abstract: With the increasing trend of using microcrystals and intense microbeams at synchrotron X-ray beamlines, radiation damage becomes a more pressing problem. Theoretical calculations show that the photoelectrons that primarily cause damage can escape microcrystals. This effect would become more pronounced with decreasing crystal size as well as at higher energies. To prove this effect, data from cryocooled lysozyme crystals of dimensions 5 × 3 × 3 and 20 × 8 × 8 µm mounted on cryo-transmission electron microscopy (cryo-TEM) grids were collected at 13.5 and 20.1 keV using a PILATUS CdTe 2M detector, which has a similar quantum efficiency at both energies. Accurate absorbed doses were calculated through the direct measurement of individual crystal sizes using scanning electron microscopy after the experiment and characterization of the X-ray microbeam. The crystal lifetime was then quantified based on the D1/2 metric. In this first systematic study, a longer crystal lifetime for smaller crystals was observed and crystal lifetime increased at higher X-ray energies, supporting the theoretical predictions of photoelectron escape. The use of detector technologies specifically optimized for data collection at energies above 20 keV allows the theoretically predicted photoelectron escape to be quantified and exploited, guiding future beamline-design choices.

Journal Keywords: photoelectron escape; CdTe detector; cryo-TEM sample mounts; microcrystals

Subject Areas: Technique Development, Biology and Bio-materials


Instruments: I24-Microfocus Macromolecular Crystallography

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