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辐射损伤是应用电子显微镜研究生物大分子高分辨结构中最棘手的问题。辐射损伤是由于样品对入射电子的散射所引起的。对于生物样品,电子散射大约有3/4是非弹性。典型的电子能量损耗是20eV。任何原子要在象中显示出来,起码要散射几个电子,因而它至少接受约100ev数量级的能量,这个值,对具有10ev的碳链来说是过高了的。高分辨成象通常需要的电子剂量约为10~4e/(nm)~2,多数的生物样品将损失其质量的20～80％,可见辐射损伤对生物样品成象的影响是严重的。克服辐射损伤的最有效办法是减少电子剂量,但剂量的减少,会使象的信噪比迅速下降,直接影响分辨率。另一办法是增加样品的抗性(resistance),其方法是冷冻样品。放
Radiation damage is the most difficult problem to study the high resolution structure of biological macromolecules by using electron microscope. Radiation damage is caused by the scattering of incident electrons by the sample. For biological samples, about 3/4 of the electron scattering is inelastic. The typical electron energy loss is 20eV. Any atom to be displayed in the image, at least to scatter several electrons, so it receives at least about 100ev energy, the value of the carbon chain with 10ev is too high. High-resolution imaging usually requires an electron dose of about 10-4 eV nm2, and most biological samples will lose 20-80% of their mass, demonstrating that the effects of radiation damage on the imaging of biological samples are severe. The most effective way to overcome the radiation damage is to reduce the electron dose, but the decrease of the dose will cause the signal to noise ratio of the image to drop rapidly and directly affect the resolution. Another approach is to increase the resistance of the sample by freezing the sample. put