Beam efficiency, inelastic scatter, and radiation damage in the high-voltage microscope

The composite plasmon-free atom scattering theory of Crick and Misell has been used to calculate the angular intensity distribution of inelastic scatter from a model biological object (50 Å of amorphous carbon) at 100- and 1000-kV acceleration voltage. It is shown that in most situations of electron microscope imaging of supramolecular structures the damage associated with viewing and recording of the image is related to the ratio of inelastic scatter/elastic scatter (I/E) or to I/(I+E), and that these ratios are approximately the same at 100 and 1000 kV. It is concluded that there is no intrinsic improvement in beam radiation damage in using higher acceleration voltage (1000 kV). In current use, the radiation damage in the high-voltage microscope (HVEM) is frequently much higher than in a conventional (100 kV) microscope, because of the decreased sensitivity of photographic emulsions at 1000 kV. Special emulsions are required for high-voltage biological electron microscopy.