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CHAPTER 1 



Principles of Radiological Physics^ 



U. Fano 



National Bureau of Standards 



Properties and production of radiations: Corpuscular radiations — Production of 

 corpuscular radiations — Electromagnetic radiation — Production of electromagnetic radia- 

 tion. Action of radiations on atoms and molecules: Summary of information on 

 atoms and molecules — Elementary processes involving radiation and free particles — 

 Action of light and X rays on atoms and molecules — Action of charged particles on atoms 

 and molecules — Nuclear collisions. Dissipation of radiation energy in matter: Activa- 

 tion by charged corpuscular radiations — Activation by X and gamma rays — Activation by 

 neutrons — Activation by infrared, visible, and ultraviolet light — Action of far-infrared and 

 radiofrequency radiation — Spatial distribution of activations — Summary. Penetration 

 of radiations in matter: Heavy charged particles — Electrons — X rays — Neutrons — Light. 

 Kinetics of radiation action: The radiation dose — Methods of expressing macroscopic 

 effects — Simple dose-effect relations — Sigmoid dose-effect curves — Tirne-intensity factors- 

 Comparative effectiveness of different radiations. References, 



This chapter deals with facts and concepts of physics which imderHe 

 the action of radiations upon matter in general and upon biological mate- 

 rials in particular. It stresses the line of thought which may be followed 

 in analyzing the radiation effects, but the reader will often be referred to 

 other sources for technical details. 



Physics has attained a fairly satisfactory understanding of the nature of 

 radiations. The direct action of radiations on single atoms or small 



1 This chapter is designed to serve workers in biology and medicine as an introduc- 

 tion to the principles of radiological physics and to give an elementary but inclusive 

 treatment of the broad question: What happens when radiation strikes a material? 

 The attempt to present such a treatment has pointed up large gaps in our knowledge, 

 the filling of which is a main goal of the current program of research in basic radiation 

 physics at the National Bureau of Standards. 



Some results of recent research supported by the Office of Naval Research and 

 the Atomic Energy Commission are included. The Biophysics Branch of the AEC is 

 supporting a project directed toward the survey and dissemination of information on 

 the action of radiations on matter. Much work specifically required for the prepara- 

 tion and illustration of this chapter has been carried out as a part of that project. 



The author wishes to thank the numerous colleagues who have contributed assist- 

 ance and advice, especially M. Lewis, F. A. Stinson, and G. R. White for the calcula- 

 tion and preparation of numerous charts. 



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