International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by M. G. Rossmann and E. Arnold

International Tables for Crystallography (2006). Vol. F, ch. 19.2, p. 423   | 1 | 2 |

Section 19.2.1. Electron scattering

W. Chiua*

aVerna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
Correspondence e-mail: wah@bcm.tmc.edu

19.2.1. Electron scattering

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When an electron interacts with a free atom, it is simultaneously attracted to the nucleus because of the nuclear positive charge and repelled by the electrons of the atom. An electron scattering event is a composite of these forces (Hirsch et al., 1977[link]). Mathematically speaking, an electron `sees' the potential function of the atom, which can be approximated as a `screened Coulomb potential function'. This function is often referred to as a mass-density function and is analogous to the electron-density function in the case of an X-ray photon, which is scattered only by the electrons of an atom.

Because of the strong interactions between an electron and an atom, the scattering cross section of an atom is much higher for electrons than it is for X-rays. For a 100 keV electron, it is about 104 times greater than for an X-ray. For every single electron scattering event of a carbon atom, there is more than a 60% probability that the electron will lose part of its energy, which is called inelastic scattering. The energy lost is primarily in the range 10 to 20 eV, which is sufficient to induce excitation and ionization of the atoms upon irradiation (Isaacson, 1977[link]). This energy transfer to a molecule results in breakage of chemical bonds and mass migration of broken molecular fragments.

References

Hirsch, P., Howie, A., Nicholson, R. B., Pashley, D. W. & Whelan, M. J. (1977). Electron microscopy of thin crystals. Huntington: Robert K. Krieger Publishing Co.Google Scholar
Isaacson, M. S. (1977). Specimen damage in the electron microscope. In Principles and techniques of electron micrsocopy. Biological applications, edited by M. A. Hyatt, pp. 1–78. New York: Van Nostrand Reinhold Co.Google Scholar








































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