X-RAY MICROSCOPY 



creased where the x-ray photons are absorbed 

 in the substrate. 



Even if an ideal recording material were 

 found, the ultimate resolution of this method 

 would be limited by the range of the photo- 

 electrons ejected by the incident x-rays. This 

 distance is about 100 A in low atomic number 

 materials for 500-volt electrons. 



A system for the direct conversion of 

 x-rays to electrons, analogous to the micro- 

 fluorographic technique for light optical 

 magnification, has been investigated by 

 Mollenstedt and Huang (34) and by Huang 

 (35). In this system the x-rays fall on a thin 

 structureless foil in the object plane of an 

 electron optical system. The specimen is in 

 contact with the foil on the x-ray side while 

 the other side serves as a type of photo- 

 cathode in the electron system. The initial 

 photoelectrons have too large an energy 

 spread to allow high resolution focusing, 

 however they give rise in the foil to tertiary 

 electrons of much lower energy which can 

 be uniformly accelerated and focused. The 



ultimate resolution of such a system will 

 again depend on the range of the initial 

 photoelectrons. 



Contact Microradiographic Apparatus 



For many applications good quality micro- 

 radiographs may be made using standard, 

 sealed-off diffraction x-ray tubes, and a 

 simple film holder for a camera. However 

 for wave lengths longer than about 2.5 A 

 or for difficult problems, special apparatus 

 may be required. At present the only com- 

 mercial apparatus specifically designed for 

 soft x-ray contact microradiography is 

 manufactured by N. V. Philips of Holland 

 (36). This instrument, designated the 

 CMR-5, is illustrated in Fig. 2. The sealed- 

 off beryllium window x-ray tube projects 

 from the side of the case which houses the 

 filament and high voltage supplies and their 

 controls. Maximum anode voltage is 5 Kv 

 and the useful spectrum ranges from about 

 3 to 12 A wavelength. With an anode voltage 

 of 3 Kv the peak of the continuous spectrum 



Fig. 2. Philips contact microradiographic apparatus, CMR-5. The x-ray tube, shown in Fig. 3, is 

 mounted in the housing projecting from the case. The case contains all of the power supplies and con- 

 trols for operation. 



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