HYDROGEN PEROXIDE PRODUCTION UNDER 

 VARYING CONDITIONS OF IRRADIATION 



M. Ebert 



Medical Research Council Experimental Radiopathology Research Unit, Hammersmith 



Hospital, London 



Aerated water is decomposed by ionizing radiation to molecular oxygen 

 and molecular hydrogen, and hydrogen peroxide is formed. These reac- 

 tions are of general interest in radiation biology for two reasons : {a) because 

 they provide information on radical reactions and interactions in aqueous 

 systems, and {b) because hydrogen peroxide is an important substance 

 biologically. 



Aqueous chemical systems exposed to radiation are known to be affected 

 by dissolved oxygen and other gases and often show a marked pH depend- 

 ence^. In radiation biology the effect of oxygen has been widely demon- 

 strated^- ^, but little is known about the effect of pH. The influence of 

 these two variables on the formation and decomposition of hydrogen 

 peroxide will be discussed in this paper. 



It has been shown^ that the concentration j of hydrogen peroxide formed 

 in aerated water by a radiation dose d can be described by the function 



where a and h are constants {see Figure 2) which are characteristic for one 

 set of experimental conditions, including radiation quality, dose rate, 

 oxygen concentration and pH. This function reaches an equilibrium value 

 for high doses, at which the hydrogen peroxide concentration is not altered 

 by a further increase in dose. At these dose levels the forward and back 

 reactions proceed at the same rate, i.e. formation and break-down of 

 hydrogen peroxide balance each other. 



Effect of dissolved gases 



The initial yields of hydrogen peroxide in water quoted in the literature 

 are very conflicting, the disagreement being much larger than can be 

 ascribed to errors in dosimetry, or analytical procedures-^ Some of the 

 difficulty may be due to the fact that molecular hydrogen and oxygen 

 are formed in water in yields comparable to those of hydrogen peroxide, 

 and both these gases react with the primary free radicals. In some experi- 

 mental conditions the gases formed cannot escape from the bulk of the 

 solution. 



The importance of this point is illustrated by an experiment in which 

 varying amounts of hydrogen peroxide were added to neutral aerated water, 

 which was then irradiated with 1 -2 MeV electrons at high dose rates. The 

 total doses delivered were approximately ten times higher than those needed 

 to produce the equilibrium concentration of hydrogen peroxide. As shown 



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