X-RAY MICROSCOPY 



Fig. 7. Commercial X-ray projection micro- 

 scope, manufactured by the electron microscope 

 division of the T(echmcal) P(hysics) D(epart- 

 ment), T.N.O. and T.H., Delft, Holland. 



The magnetic objective has a focal length 

 of about 1.8 mm. It consumes 90 W and is 

 water-cooled. As the specimen and target 

 are inserted sidewards, the gap between the 

 pole pieces is made relatively large (ca. 7 

 mm). The specimen carrier can be moved 

 independently in three directions, the mag- 

 nification on the film is variable between 

 150 X and 10 X. The admissible optical mag- 

 nification of the film is approximately 10 X . 

 To realize the two extreme values of the mag- 

 nification the specimen must be put very 

 close to the target in the first case and almost 

 at the upper pole piece in the second case. 

 As a result the magnification cannot be 

 varied continuously over the whole range. 

 Without breaking the vacuum, the specimen 

 holder can be turned over 180° after a small 

 outward movement. For a magnification 

 greater than 150X either the specimen must 

 be fixed on the target carrier or the target 

 fixed on the specimen carrier. To accomplish 

 this the target holder can be completely 

 moved outward. Furthermore, it can be 

 moved in a plane perpendicular to the optical 

 axis, thus allowing the use of a clean part 

 of the target for each exposure (See Fig. 9). 

 The target holder can contain up to four 

 different materials in the form of thin, 

 evaporated or rolled metal films. 



The x-ray fluorescent screen is fixed on an 

 aplanat and vie\ved with a binocular (two 

 separate objectives) viewer (IG). As focus- 

 ing is carried out with the reflected elec- 

 trons and the fluorescent image is inadequate 

 for visual observing, this part of the micro- 

 scope should be considered as a view-finder. 

 Hence, the image brightness is more impor- 

 tant than the magnification. Thus the former 

 is increased at the expense of the latter. The 

 total optical magnification of this finder 

 system is some 20 X. The screen and aplanat 

 can be moved away so that the specimen 

 can be viewed with the binocular for prehmi- 

 nary positioning. 



In contrast with other projection units, 

 the specimen as well as the camera is in 

 vacuum for the following reasons. By using 

 either very high or very low voltages, the 

 target thickness must be equal to or less 

 than the resolution. This is necessary to re- 

 duce the effect of electron diffusion in the 

 target in the first case and to avoid too much 

 absorption of the x-rays in the second case. 

 Such a target is inadequate as a vacuum seal 

 unless its area is very much restricted. Fur- 

 thermore, the air between source and film 

 would absorb too much soft radiation. A 

 direct advantage of a non-sealing target is 

 that it can be easily exchanged during 

 operation and that a clean part can be used 

 for each exposure. The restriction that only 

 dry specimens can be used is not considered 

 to be a serious one. The new instrument, 

 however, is designed in such a way so as to 

 allow the target and specimen stage to be 

 exchanged for another one with a vacuum 

 sealing target. The author has no informa- 

 tion yet about the design and execution of 

 this particular part. 



The camera is designed for 20 exposures 

 on 35 mm film. The film is transported auto- 

 matically by moving the camera back and 

 forth. A shutter is provided, which opens in 

 exposure position. For short exposure, the 

 intermediate target, which lies between ob- 

 jective and condenser may be used to inter- 



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