CONTACT MICRORADIOGRAPHY 



is at 6.5 A, which is useful for a wide range 

 of histological specimens. Figs. 3 and 4 show 

 cross sections of the x-ray tube and camera. 



]\Iany tubes for contact microradiography 

 have been specially constructed, and the 

 details of their operation may be found in 

 the references. Efforts have concentrated on 

 achieving focal spots smaller and more 

 brilliant than standard diffraction tubes, 

 as in the Ehrenberg and Spear microfocus 

 tube (37), or in reaching the ultrasoft wave- 

 lengths as in the tubes described by Eng- 

 strom and Lindstrom (38) for historadio- 

 graphic analysis, and by Engstrom et at. 

 (39) and Henke (13) for wave lengths in the 

 20 A region. Other tubes and cameras for 

 microradiography are described by Fitz- 

 gerald (40) Ely (41), Salmon (42), Greulich 

 (43), and Recourt (23). 



For realizing the optimum conditions of 

 intensity and resolution for the contact 

 x-ray image the source must have an ad- 

 justable diameter as well as a variable 

 spacing from the specunen and recording 

 material, as previously pointed out. Also 

 for good contrast in different specmien 

 materials or thicknesses the target material 

 should be easily changeable and the anode 

 voltage adjustable. 



In many specific applications such re- 

 finements are not worth the effort. However, 

 for microfluoroscopic viewing the maximum 

 intensity must be available for a clearly 

 visible image. This requirement led to the 

 design of an instrument shown schematically 



Fig. 3. Cross-section of x-ray tube for micro- 

 radiography between 1.5 and 5 kV. 1 , cathode with 

 tungsten filament; 2, anode with tungsten target; 

 3, beryllium window 50 microns thick. The tube is 

 8 cm long. The (effective) size of the focal spot is 

 0.3 X 0.3 mm. 



Fig. 4. The target end of the x-ray tube, show- 

 ing attached cjdinder into which the film-holder is 

 inserted. Underneath is the film-holder itself, 

 loaded with film, specimen and specimen carrier. 

 The pressure plate is in the form of a plunger 

 which, under the action of a spring 5, keeps the 

 film, specimen and specimen carrier (^4) pressed 

 against a rubber ring 1 . The other rubber rings (2, 

 3 and 4) ensure a good seal, making it possible to 

 evacuate the film-holder bj' attaching a vacuum 

 line (a water-jet pump provides sufficient vacuum) 

 to the nozzle provided for the purpose. 



ELECTRON 

 GUN 



ELECTRON 

 LENS 



TARGET 



FLUORESCENT 

 SCREEN 



VIEWING 

 EYEPIECE 



ILLUMINATOR 



Fig. 5. Schematic diagram of the microfluoro- 

 scope. 



567 



