518 



H. GRAY 



Dale, Meredith, and Gray (33) suggest that herein Hes the explana- 

 tion of the high yield of hydrogen peroxide production and of de- 

 composition, observed when air-free water is irradiated with a rays 

 but not observed with X rays and other less densely ionizing radia- 

 tions. 



On the other hand, Allen (103) has concluded from studies of the 

 influence of hydrogen gas pressure on the equilibrium concentration 

 of H2O2 that results from the exposure of water to intense beams of 

 electrons and deuterons that, at any rate under the conditions of his 



-0.08 -0.04 0.04 0.08 



DISTANCE (r) FROM CENTER OF COLUMN IN MICRONS 



Fig. 10. Curves showing progressive diffusion of hydroxyl radicals 

 derived from positive ions and hydrogen atoms derived from negative 

 ions formed by an a particle (104). 



experiments, the poor yield obtained with electrons is mainly due to a 

 back reaction involving molecular hydrogen, which takes place 

 throughout the bulk of the solution and not specifically along the 

 tracks. Since important constants in Lea's calcvilations are very im- 

 perfectly known at present, the relevance of initial combination of 

 radicals to the interpretation of particular radiochemical reactions 

 cannot yet be properlj^ assessed. Nevertheless, the differences de- 

 picted in Figures 9 and 10 represent a second and distinct aspect of 

 ion density dependence relevant to the interpretation of radiochemical 

 studies. Furthermore, evidence is accumulating in favor of the view 

 that, even in cases, as for example chromosome fragmentation, in 

 which the visible damage to a particular structure has correctly been 

 ascribed to the action of a single ionizing particle, the damage may 



