44 



W. C, NIXON 



radiography were described and micrographs dem- 

 onstrated the results obtained. Dr. Ehrenberg and 

 Mr. White, London, spoke of their use of total 

 reflection to select long wavelengths, 8-10 A, for 

 contact microradiography. Thin emulsions give a 

 resolution approaching 0.1 // and yet the intensity 

 is high enough for only 5 minute exposures. Prof. 

 Engstrom and others from Stockholm discussed the 

 use of the Henke source of soft x-rays (equal to 

 200-2000 volts) and excellent results were shown of 

 the chromosomes in the onion root tip with a resolu- 

 tion equal to the light microscope. Dr. Recourt, 

 Eindhoven, also used x-rays generated below 1000 

 volts with the Philips unit without a window. Again 

 high resolution, less than 0.3 //, was shown and 

 excellent contrast. 



Dr. D. Jones, Tubingen, described a new method 

 of x-ray microscopy, worked out with Prof. Mollen- 

 stedt, whereby the photoelectrons emitted after the 

 x-rays pass through a specimen in the contact micro- 

 radiographic method, strike a metal foil and emit 

 low energy secondary electrons. These are then 

 focused by an electrostatic lens to give an enlarged 

 image of the x-ray contrast. This is contact radio- 

 graphy plus image conversion and brings the number 

 of methods of x-ray microscopy up to ten. Again, a 

 resolution of 1 // or better was shown. 



Scanning x-ray microscopes were discussed by Dr. 

 Pattee, Stanford, and Mr. Duncumb, Cambridge. 

 Paper B 2 of this conference covers the same field, 

 so no summary is given. The scanning method of 

 microanalysis as shown by Duncumb was a high 

 point of the symposium and future results are eagerly 

 awaited. 



The possibilities of extending the resolution of 

 contact microradiography beyond the light micro- 

 scope were shown by Mr. and Mrs. Ladd, New York, 

 with their plastic process. A grainless plastic is 

 exposed to x-rays and developed by acetone dissolv- 

 ing of the unaffected areas. A replica of the surface 

 is then viewed by electron microscopy. The 24 hours" 

 exposure times limit the process and Dr. Pattee and 

 Mr. Warnes, Stanford, showed similar results using 

 Saran plastic and a few hours' exposure. 



Two papers of Gabor diffraction with x-rays were 

 read by Dr. El-Sum, Stanford, and Dr. Baez, Red- 

 lands, California, and the difficulties of fringe forma- 

 tion discussed. Finite source size, wavelength spread 

 and x-ray transparent objects all diffuse the fringe 

 pattern and diftYaction holograms are difficult if not 

 impossible to make. 



Microanalysis formed a large part of the program 

 as this is one area where the use of x-rays is superior 

 to light or electrons for many specimens. Micro- 

 diffraction cameras for the Hilger and Watts Ehren- 

 berg and Spear microfocus tube were discussed by 

 Dr. Ehrenberg, London, and Dr. Nixon, Cambridge, 

 showed some results using the Cosslett-Nixon point 

 source tube as a source for micro-beam x-ray dif- 

 fraction. 



Dr. Lindstrom, Stockholm, described quantitative 

 methods of microchemical analysis by contact micro- 

 radiography and showed an analysis of 1.3 % of 

 sulphur in skin over a 10 // area. Dr. Wallgren, 

 Stockholm, has studied developing embryonic bone 

 in this way to discover the extent of mineralization. 

 Dr. Hallcn, Gothenburg, showed some aspects of 

 automation in contact microradiography using a 

 new scanning and computing microphotometer to 

 analyse the microradiograph. Mr. Long and Mr. 

 Duncumb, Cambridge, discussed quantitative pro- 

 jection methods of microanalysis. 



Results of the various methods included botanical, 

 biological and metallurgical samples primarily. With 

 the contact method Dr. Salmon, Paris, presented a 

 complete review of botanical microradiography on 

 normal and cancerous leaves and stems and other 

 areas. Correlation with autoradiography and polar- 

 ization microscopy was made with the x-ray method 

 giving the best indication of chemical structure. Dr. 

 Bohatirchuk, Ottawa, discussed applied microradio- 

 graphy in medical research, particularly bone studies 

 and Dr. Recourt, Eindhoven, was able to follow 

 staining by osmium tetroxide by contact micro- 

 radiography. Human cervical cancer has been studied 

 by Dr. Fitzgerald, New York, and human breast 

 cancer by Dr. Leborgne, Montevideo. Both are 

 using contact microradiography in an exploratory 

 way and need more results before interpretations 

 can be made. Prof. Saunders, Halifax, presented 

 two papers, one on dental pulp vessels using a 

 suction-injection technique with thorotrast and the 

 other on vascular patterns in muscle, also using 

 contrast media. Both of these papers showed the 

 excellent results possible with normal x-ray equip- 

 ment and good specimen preparation. Dr. Carr, 

 Bradford, discussed renal calculi observed by con- 

 tact microradiography and other papers showed 

 results on bone and the human eye. 



Metallurgical contact microradiography was rep- 

 resented by fewer papers but showed the results of 

 a great deal of work. Mr. Andrews and Mr. Johnson, 

 Rotherham, discussed iron and steel research, par- 

 ticularly segregation and sintering. Mr. Sharpe, Bristol, 

 showed many results of alloys and inclusions, and 

 discussed metal specimen preparation. Drs. Votava, 

 Berghezan, and Gillette, Brussels, found very strong 

 Bragg reflection giving contrast from pure samples 

 due to the different crystal orientations and used 

 this to study imperfections in the crystals. 



The projection method of x-ray microscopy was 

 represented by Mr. Jackson, Cambridge, on wood 

 sections, geological (pitch blende) and metallurgical 

 (Al-3 "^'o Mn) samples, and by Mr. Smith, Cambridge, 

 on insect flight musculature. 



The main conclusions of the conference concerned 

 the high degree of interest in this subject and a 

 committee of three. Dr. Cosslett, Cambridge, Prof. 

 Engstrom, Stockholm, and Prof. Kirkpatrick, Stan- 

 ford, was formed to ensure continuance of the ties 



