DISCUSSION OF MORRISON'S AND FANO'S PAPERS 23 



Burton: 



Ionization potentials are really different in the gas phase and in the liquid 

 phase. It is very likely that they are lower in the latter merely because of the 

 effect of dielectric constant — a very substantial matter in aqueous systems. 

 Thus, statements of jdeld per ion pair based on the assumption of, for example, 

 32.5 ev required per ion pair are definitely wrong. I think that we may object 

 to the usage even if we recall that calculated ion-pair yields are merely a con- 

 vention, for the numbers we thus derive are definitely prejudicial to the theory. 

 During the war years on the Atomic Energy Project we adopted, instead, the 

 convention of 100-ev yield, the number of molecules converted per electron volt 

 absorbed. The convention has the merit that ordinary 100-ev yields in simple 

 cases without important chain and without important back reactions turn out 

 to be of the order of unity (that is, up to 6 or some such figure). Another merit 

 is that no one is tempted to place any inherent theoretical emphasis on a number 

 so calculated. 



Aebersold: 



Morrison has given us a very excellent summary of the state of knowledge of 

 the physical processes resulting in matter from ionizing radiations. I was par- 

 ticularly interested in his remarks concerning the time scale of the sequences 

 that follow the passage of an ionizing particle. Before World War II those of 

 us who were interested in comparing the results of different types of ionizing 

 radiation kept in mind the immediate physical picture, as developed by Lea 

 and others, of the ion clusters produced by the particles. This, I gather from 

 Morrison, is the picture at 10~^* to 10"^^ sec after passage of the particle, and 

 that actually the more important picture for comparative purposes is the position 

 of the affected atoms and molecules at later times, say 10~'^ to 10~^ sec. Would 

 Morrison care to review for us the comparative picture of the state and position 

 of the affected molecules and atoms resulting from passage of a 1-mev beta 

 particle and a 1-mev proton at these later times? 



Morrison : 



This is a difficult subject, since, in the subsequent motion, caging, recombina- 

 tion, and other factors are involved. Our knowledge of what occurs in the col- 

 umns of ionization from different particles with varjang ionization densities is not 

 adequate. We know the events up to 10"^- sec in gases. The question of the 

 conversion of electron energy and excitation in complex molecules is not clear 

 at the present time. 



Tobias: 



I should like to make a comment and ask a question. It was implied in the 

 foregoing discussion that ionization of the less abundant cell constituents may 

 be neglected on account of the small quantity of these elements. In this con- 

 nection one should mention that an atom of an element with high atomic number 

 will, on the average, more frequently become ionized than an atom mth low 



