X-RAY MICROSCOPY 



condition cannot be fulfilled by the contact 

 mefhod where a is larger by at least two 

 orders of magnitude. If equation {5) is not 

 fulfilled, a distortion in the depth dimension 

 occurs. This can easily be shown in Fig. 13. 



Let ^ , -Bo , Co , and Do be four points 

 equally spaced along a line. Let, furthermore, 

 S> be the projection center (x-ray source), F 

 be the film and Ap , Bp , Cp , and Dp the pro- 

 jected points, li AqDo is a reasonable fraction 

 of ^o*S, (Fig. 17a), then ApBp 9^ BpCp ^ 

 CpDp . If, however, AS » AqDo (See Fig. 

 13b), the rays A^Ao \\ BoB, \\ CoCc \\ DoDc 

 thus AcBe = B,.Ce = CcD, . When after 

 processing and magnifying, the film is 

 viewed, the resulting points seem to come 

 from Av , By , Cv , and Dy ; now AvBy 9^ 

 ByCv 9^ CvDv . For depth measurements, 

 however, the last method is preferable be- 

 cause the ratio of the distances on the film 

 and depth dimension of the specimen re- 

 main the same. This results in better ac- 

 curacy. 



The depth of field must be a reasonable 

 fraction of the source-to-specimen distance. 

 An object with a depth dimension of some 

 15 cm and placed with the shortest distance 

 to the observer of 30 cm can still be sur- 

 veyed. In terms of our considerations, this 

 means that the depth of focus of the micro- 

 scope must be a reasonable fraction of the 

 distance a. For microscopes using an optical 

 system, the focal length / should be used in- 

 stead of a. So this condition cannot be ful- 

 filled. The only microscopes where all these 

 conditions can be met are the camera obscura 

 and the projection microscope. 



The use of x-rays for stereoscopic examina- 

 tion has many advantages over using ordi- 

 nary light. Besides the possibility of observ- 

 ing opaque parts, the negligible refraction, 

 and reflection make any part of the specimen 

 observable. (Compare the visibility of a 

 specimen behind a ground glass screen.) 



(The pictures shown in this article were 

 kindly supplied by the Electron Microscope 



Division of the Technical Physics Depart- 

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



REFERENCES 

 SiEVERT, R., Ada Rad., 17, 299 (1936). 



ROVINSKY, B. M., LUTSAU, V. G., AND AVDE- 



YENKO, A. I. "X-ray Microscopy and Micro- 

 radiography," Academic Press, p. 269, New 

 York, 1957. 

 Ardenne, M. von, Naturwiss., 27, 485 (1939). 



COSSLETT, V. E., AND NiXON, W. C, Natl. 



Bur. Stand. Symposium (1951), Circular 527, 



p. 257. 

 Cosslett, V. E., Nixon, W. C, and Pearson, 



H. E., "X-ray Microscopy and Microradi- 

 ography," Academic Press, p. 96, New York, 



1957. 

 Le Poole, J. B. and Ong Sing Poen, Ibid., 



p. 91. 

 Newberry, S. P. and Summers, S. E., Ibid., 



p. 116. 

 Bessen, I. I., Philips Electronic Inc., Engi- 

 neering report #66, (1958). 

 Ong Sing Poen and Le Poole, J. B., Proc. 



4th Int. Conf. Elec. Mic, Berlin, (1958). 

 Liebmann, G. and Grad, E. M., Proc. Phys. 



Soc, B64, 56 (1951). 

 Dorsten, a. C. van and Le Poole, J. B., 



Phil. Tech. Rev., 17, 47 (1955). 

 Ong Sing Poen, "Microprojection with X- 



rays," p. 71, Martinus Nijhoff, The Hague, 



1959. 

 Nixon, W. C, Proc. Roy. Soc, A232, 475 



(1955). 

 Ong Sing Poen and Le Poole, J. B., Appl. 



Sci.Res. B, 7, 233 (1958). 

 Cosslett, V. E., Proc. Phys. Soc. B, BXV 782 



(1952). 

 Ong Sing Poen, "Microprojection with X- 



rays," p. 31 Martinus Nijhoff, The Hague, 



1959. 

 Ong Sing Poen, Ibid., p. 74. 

 Mosley, V. M. AND Wyckoff, W. G., J. 



Ultracelstructure Res., 1, 337 (1958). 



BoTDEN, p. J. M., COMBEE, B., AND HOUT- 



MAN, J., Phil. Tech. Rev., 14, 114 (1952). 



Ong Sing Poen 



REFLECTION MICROSCOPY (KIRKPATRICK) 



Since Rontgen's first unsuccessful experi- 

 ments in attempting to concentrate x-rays 

 by lenses and mirrors, many similar efforts 



6 



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8 



9 



10 



11 



12, 



13. 

 14. 

 15. 

 16. 



17. 

 18. 



19. 



672 



