X-RAY MICHOSCOPY 



Fig. 11. Showing the three sections, the baffle 

 and trap, the x-ray source, and the camera. 



tensity is required for precise measurements 

 to be made within one square micron of area 

 or less — this fact is clearly evidenced by the 

 requirement for very high-intensity light 

 sources in ordinary microphotometry of such 

 resolution. And, as indicated earlier, because 

 of the very low efficiency of production of 

 ultrasoft radiations, such high image intensi- 

 ties are extremely difficult to realize. The 

 amplification of the x-ray "signal," resulting 

 from the development of the photographic 

 image, has made this method highly efficient. 

 The resolution of the finest grain photo- 

 graphic emulsions which are currently avail- 

 able, e.g., Eastman Spectroscopic-649, is be- 

 tween 0.1 and 1.0 micron, depending upon 



the contrast and density of the image. The 

 resolution for line gratings or grids (lines per 

 mm resolution of black and white areas) is 

 equal to or better than that for the light 

 microscope itself. However the spatial reso- 

 lution needed, for example, in the measure- 

 ment of the variation of mass thickness, as 

 measured across an image of a biological cell, 

 is limited to about 0.5 fx so that the recording 

 material and not the light optical measure- 

 ment becomes the limiting factor. 



The writer has made some preliminary 

 measurements on very thin "grainless" phos- 

 phors used as recording material, photomi- 

 crographing the fluorescent image during the 

 x-ray exposure. These were made by the 

 evaporation of Mn-activated Zn2Si04 (ob- 

 tained from General Electric) according to 

 the method developed by Feldman and 

 O'Hara (6). It was hoped that, at the ex- 

 pense of sensitivity, higher resolution might 

 be gained. Measurements from thin layers 

 of this phosphor evaporated upon quartz 

 cover-slips have indicated comparable granu- 



FiG. 12. The complete ultrasoft x-ray micro- 

 radiographic analysis system with power supply 

 and vacuum gage circuit. 



686 



