103 



IMPORTANCE OF RADIATION CHEMICAL EFFECTS IN RADIOBIOLOGY 



Martin Kamen 



I thought what I would do would be to go through my notes and attempt to re- 

 capitulate briefly what has happened at this Conference. 



On the first day we were told about some recent findings concerning stopping 

 power of various media for various radiations. Actually this is not a matter of 

 primary interest to radiobiologists. The only immediate field in which this 

 subject may be of interest relates to dosage and dosage units. 



Among the topics discussed on the first day there was some mention of 

 change in the value for the mean energy required to produce an ion pair in any 

 given gas. As long as air is not mentioned nobody is perturbed. The whole 

 system of dosage units depends on the measurement of the mean energy required 

 to produce an ion pair in air. It does not have to, but it does. Because the 

 clinical radiobiologists tenaciously cling to the roentgen as a unit for X ray 

 measurement it is going to be necessary to pay some attention to what the ion- 

 pair energy is in air. As noted here, it seems that the major differences have 

 been found in the rare gases, and that these differences, which are quite large, 

 arise from the presence of small amounts of impurities. By some strange 

 chance, the standard medium chosen by the biologists for dosage happens to be 

 one of the most impure things known -- air. So the probability that an impurity 

 makes any difference in any further determination of the ion energy is quite nil. 

 Maybe the extension of these same types of measurements to air may show dif- 

 ferences, but it is doubtful. So I don't think we have to concern ourselves with 

 any possible developments in this direction. This is my opinion and if anybody 

 thinks differently he can certainly say so as we go along. I don't want to give 

 the impression that this is going to be a steam-roller type of lecture. 



ZIRKLE: I think you do us biologists a slight injustice in blaming us for the 

 roentgen. We have accepted it as a necessary evil in estimating the energy 

 transferred to tissue. 



KAMEN: I think you are right. My choice of words was unfortunate. What 

 I mean is that there is no way of getting around using the r at the present time. 



There is a great paucity of data about what happens when electrons are 

 slowed down to various low energies, and inasmuch as we do not know at the 

 present time what fraction of the total track is effective in radiobiology it may 

 be of some importance to determine just how much time an electron spends in 

 lower energy states. Roughly, I think one would say that the chance of getting 

 something to happen at a particular place depends upon how much time the elec- 

 tron is around there, and it is obvious that most of the time the electron spends 

 is in the lower energy region. So since there is little known about the penetra- 

 tion of such electrons, there is an extremely deplorable gap in the data. It is a 

 good thing that Dr. Pollard and others have begun to try to get data on the pene- 



