Specimen Behavior in the Electron Beam

It has long been known that cryo-EM specimens are severely damaged by a level of electron exposure that is much lower than what is needed to obtain high-resolution images from single macromolecules. Perhaps less well appreciated in the cryo-EM literature, the vitreous ice in which samples are suspended is equally sensitivity to radiation damage. This chapter provides a review of several fundamental topics such as inelastic scattering of electrons, radiation chemistry, and radiation biology, which-together-can help one to understand why radiation damage occurs so "easily." This chapter also addresses the issue of beam-induced motion that occurs at even lower levels of electron exposure. While specimen charging may be a contributor to this motion, it is argued that both radiation-induced relief of preexisting stress and damage-induced generation of additional stress may be the dominant causes of radiation-induced movement.