122 Applied Biophysics 



radiation, and is roughly the same for beta rays (A ^ 10) and 

 alpha rays (A = 3,500 ).t This is true of the decomposition of 

 ammonia, nitrous oxide, and hydrogen iodide. The decompo- 

 sition of water vapor, however, appears to be exceptional in 

 that the yield is very low with X-rays. Equality of yield with 

 beta and alpha radiation has also been observed in the case of 

 the synthesis of ammonia, hydrogen bromide, and ozone, and 

 though there are no published data of this sort for neutrons or 

 other radiations of intermediate ion density, it may be presumed 

 that the yield will be completely independent of ion density in 

 those cases in which it is the same for beta and alpha rays. 



Chemical reactions in solution, and particularly in dilute 

 aqueous solution, are of much greater interest from the biological 

 standpoint. The decomposition of water itself is notoriously 

 controversial, even in regard to the experimental facts, and it is 

 not possible to say with certainty whether the much higher 

 yield generally found with alpha radiation '^' ^■'^' -'' than with 

 X-rays "*' ^^' ^^ is to be referred to differences in ion density 

 or to extraneous circumstances, such as the presence or absence 

 of dissolved oxygen. 



The position, as far as the published findings are concerned, 

 is hardly less satisfactory with regard to dilute solutions, since 

 there appears to be no reaction which has been studied at two 

 different ion densities by the same author, and the difficulties 

 associated with these experiments are such that small differences 

 in the yield obtained by different authors cannot be relied upon. 

 The evidence in the case of the decomposition of hydrogen 

 bromide and hydrogen iodide, and the reduction of potassium 

 permanganate, points to the absence of any dependence on ion 

 density. It seems fairly clear, on the other hand, that the dif- 

 ference between Stenstrom and Lohmann's estimated yield 



M 

 ( — = 0.1) for the decomposition of tyrosine by X-rays and 



N 



M 

 Nurnberger's figure ( — = 0.003)-^* for alpha ravs is evidence of 



t The symbol A will be used throughout for the linear ion density, i.e., the 

 average nximber of ions formed per micron in water. 



