Limitations to significant information in biological electron microscopy as a result of radiation damage

Reciprocity of specimen lifetime and current density at the specimen demonstrates the absence of any dose-rate effect, such as specimen heating, as a cause of specimen damage within the range 10−3 to 10−5 amperes/cm2 current densityat the specimen.

Abstract

Quantitative measurements of radiation damage in crystalline specimens of l-valine, adenosine, and catalase (uranyl acetate stained) have been made by observing the loss of the electron diffraction pattern. Reciprocity of specimen lifetime and current density at the specimen demonstrates the absence of any dose-rate effect, such as specimen heating, as a cause of specimen damage within the range 10−3 to 10−5 amperes/cm2 current density at the specimen. Specimen lifetimes at high voltages are about two and a half times greater than at conventional voltages, and it is shown that this is consistent with the dependence of linear energy loss upon accelerating voltage. The limiting resolution for meaningful observation is considered in terms of the statistics of observation at partticle fluxes that are specified from the specimen lifetime data. The best values are probably not better than 50 A for l-valine, 20 A for adenosine, and 15 A for catalase.