Ill 



IONIZATION AND ITS BEARING ON THE BIOLOGICAL EFFECTS 



OF RADIATION 



G. Failla 



Memorial Hospital, New Yo7'k 



Fundamental character of ionization. Distribution of ions in an ionized medium. 

 Interaction of radiation and matter. Influence of the quality of radiation on the distribu- 

 tion of ions in living matter. Intensity of radiation and inverse square law. Influence 

 of juatter on the intensity of radiation. Secondary phenomena. Filtration. Essen- 

 tial factors for the correlation of ionization and biological effects. Effective intensity of 

 radiation. Significance of ionization measurements. Knowledge of ionization pro- 

 duced in irradiated organism all important. Effective quantity of radiation. References. 



The law of conservation of energy tells us that if a change has been 

 brought about in a system by external means, then some energy must 

 have been supplied to the system from the exterior. Thus, if a living 

 cell is altered in any way by exposure to radiation, it must have received 

 some energy which at least initiated the change. In this sense the cell 

 may be compared to a radio receiver and the source of radiation to a 

 broadcasting station. Under certain conditions the radio "picks up" 

 a signal which initiates a series of changes in the receiver, and the listener 

 hears it. The energy required to produce the audible signal is very much 

 greater than that in the incoming wave which actuated the detector, and 

 this energy is supplied by the local source at the receiver. But energy, 

 however small in amount, must be supplied to the detector in order to 

 initiate the change. Furthermore, the energy must be delivered in a 

 certain form — in this case electromagnetic waves of a certain frequency 

 range. Similarly, the living cell exposed to radiation receives a small 

 amount of energy which initiates certain changes requiring much more 

 energy to bring to completion, this energy being supplied by chemical 

 changes in the cells. The initial actuating energy must also be in a 

 certain form — visible light, X-rays, etc. Energy can be transferred to the 

 cell by the radiation only through the interaction of matter and radiation. 

 Hence the understanding of this interaction is essential to the proper 

 interpretation of the biological effects of radiation. 



FUNDAMENTAL CHARACTER OF IONIZATION 



The conditions necessary and sufficient for the production of ions by 

 radiation in a given material have been set forth by K. K. Darrow. 



87 



