Radiation Damage and High Resolution Biological Electron Microscopy

The task of obtaining high resolution images that contain useful information in a size range smaller than 10Å to 15Å has proven to be much more difficult in the case of biological and organic specimens than in the case of inorganic materials. One of the fundamental difficulties that limits these efforts is the fact that organic materials are almost always much more susceptible to radiation damage than are inorganic specimens. If meaningful results are to be obtained, the total electron exposure must be kept below some maximum “critical exposure”, such that the amount of damage that does occur is still below a specified, acceptable level. When the allowed, “critical” exposure is very low, then fluctuations in the number of electrons collected per resolved picture element will be relatively high. At some point these fluctuations are so severe that it becomes impossible to see the actual structure of the image.