Spatial Dependence and Mitigation of Radiation Damage by a Line Focus Mini Beam
Recently, strategies to reduce primary radiation damage have been proposed which depend on focusing X-rays to dimensions smaller than the penetration depth of excited photoelectrons. For a line focus as used here the penetration depth is the maximum distance from the irradiated region along the X-ray polarization direction that the photoelectrons penetrate. Reported here are measurements of the penetration depth and distribution of photoelectron damage excited by 18.6 keV photons in a lysozyme crystal. The experimental results showed that the penetration depth of {approx}17.35 keV photoelectrons is 1.5 {+-} 0.2 {micro}m, which is well below previous theoretical estimates of 2.8 {micro}m. Such a small penetration depth raises challenging technical issues in mitigating damage by line-focus mini-beams. The optimum requirements to reduce damage in large crystals by a factor of 2.0-2.5 are Gaussian line-focus mini-beams with a root-mean-square width of 0.2 {micro}m and a distance between lines of 2.0 {micro}m. The use of higher energy X-rays (>26 keV) would help to alleviate some of these requirements by more than doubling the penetration depth. It was found that the X-ray dose has a significant contribution from the crystal's solvent, which initially contained 9.0%(w/v) NaCl. The 15.8 keV photoelectrons of the Cl atoms and their accompanying 2.8 keV local dose from the decay of the resulting excited atoms more than doubles the dose deposited in the X-ray-irradiated region because of the much greater cross-section and higher energy of the excited atom, degrading the mitigation of radiation damage from 2.5 to 2.0. Eliminating heavier atoms from the solvent and data collection far from heavy-atom absorption edges will significantly improve the mitigation of damage by line-focus mini-beams.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- Sponsoring Organization:
- DOE - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 1004988
- Report Number(s):
- BNL-94619-2011-JA; R&D Project: LS001; KC0401030; TRN: US1101073
- Journal Information:
- Acta Crystallographica. Section D, Biological Crystallography, Vol. 66, Issue 12; ISSN 0907-4449
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ABSORPTION
ATOMS
DECAY
DIMENSIONS
DISTRIBUTION
FOCUSING
LYSOZYME
MITIGATION
PENETRATION DEPTH
PHOTONS
POLARIZATION
RADIATIONS
SOLVENTS
SPACE DEPENDENCE