1. Wilken B. and Fritz T. A., Nucl. Instrum. Methods, 138 (1976) 331.
2. Cosslett V. E. and Thomas R. N., Brit. J. Appl. Phys., 15 (1964) 1283.
3. Reed S. J. B., Electron Microbe Analysis (Cambridge University Press, Cambridge) 1975.
4. Bohr N., Kgl. Dansk. Videnskab. Selskab. Mat. Phys., 18 (1948) 8.
5. Bethe H. A. and Askin J., Passage of radiation through matter, in Experimental Nuclear Physics, edited by E. Segrè, Vol I (J. Wiley and Sons, New York, N.Y.) 1953.