Radiation damage

Dommages causés par les radiations (Fr). Strahlenschäden (Ge). Danni da radiazioni (It). Daño por radiación (Sp). Радиационное повреждение (Ru).

Damage caused to the crystals by the X-Ray beam [1], resulting into the change of the ordered structure of crystalline material. Very rarely these changes may be beneficial, but generally they cause harmful modifications of properties. Electrons, which have stronger interaction with matter (as X-rays for example), can produce more radiation damage on organic samples than commonly used sources of X-rays. For electron diffraction applications, cryogenic conditions are very important for those organic molecules which will not survive the e- beam exposure at room temperature. Cryogenic measurements not only minimize radiation damage but often lead to improved resolution owing to decrease in thermal motion in the crystal.[2]

A major obstacle in macromolecular crystallography has been the radiation damage caused by the absorption of the X-ray radiation by the crystals during the diffraction experiments. Free radicals are generated when X-rays are absorbed by macromolecular crystals. These radicals propagate changes that manifest in two ways: as global effects and as site specific structural changes. Global radiation damage is observed as a loss of diffraction intensity, an increase in unit-cell volume, and higher Wilson B-factors, all due to the overall increase in non-isomorphism in the crystal. On the other hand, site specific damage, which also contributes to the global effects, is seen in the electron density maps following structure refinement.[3]

References:

1 G. Zaloga & R. Sarma, Nature,1974, 251, 551-552.

2 E. Prince, “International tables for crystallography”, Volume C, 3rd Ed., Kluwer Academic publishers, Dordrecht/Boston/London 2004, 166.

3 H. Taberman, Crystals, 2018, 8(4), 157-169.