X-ray microscope which uses a system of two magnetic lenses (Figure 

 11-32). The X-ray beam diverges on traversing the foil or target and 

 falls on the specimen, which is placed between the target and photo- 

 graphic plate. An enlarged shadow image of the specimen is projected 

 onto the photographic plate as the result of the passage of the X rays 

 through the specimen. In the compound X-ray microscope, reflecting 

 curved mirror surfaces may be used instead of electromagnetic lenses to 

 focus the X-ray beam source. Figure 11-33 shows the principle of X-ray 



Figure 11-32. Schematic Diagram of X-Ray Shadow Projection Micro- 

 scope Using Electromagnetic Lenses to Focus the Electron Image. L^, con- 

 denser lens; L,,, objective lens; T, metal foil target; O, object. (From Cosslett, 

 V. E., 1955. "Electron Microscopy," in Oster, G. and Pollister, A. W. (Eds.), 

 "Physical Techniques in Biological Research," 1, Academic Press, New 

 York, N. Y., Fig. 23, p. 526.) 



focusing, using curved mirror surfaces. By taking advantage of the ability 

 of a cylindrical curved surface to concentrate X rays in one plane only, 

 two such mirrors can be combined to give fine focusing. A simplified 

 version of the reflection type compound X-ray microscope is shown in 

 Figure 11-34. The lower part of the drawing shows the usual arrange- 

 ment for reflection X-ray microscopy. A mirror block serves to focus 

 the enlarged shadow image of the specimen onto the photographic plate. 

 In the upper part of the drawing, the X-ray tube or source is shown 

 moved to the opposite end of the system. The reflection microscope in 

 this arrangement can be used "backwards" for X-ray diffraction. The 

 radiation emitted by the X-ray tube is delimited by means of an aperture 

 to produce a narrow X-ray beam. On passing through the microscope 



254 / CHAPTER 11 



