M. EBERT 



in Figure 1, the final yield for a given dose was proportional to the amount 

 of hvdi'ogen peroxide added before irradiation. The slope of the curve 

 depended both on the dose rate and on the depth of the solution, being steeper 

 for higher dose rates and deeper solutions. In the experiment illustrated, 

 the irradiation vessels were Petri dishes 35 mm in diameter, and the solution 

 was only 3-5 mm deep, conditions which would at first sight appear to favour 

 the ready diffusion of gases. These results suggested that oxygen was 

 formed by radiolysis of the hydrogen peroxide initially present, and, at the 

 high dose rates used, could not escape, and therefore supersaturated the 

 solution. To avoid this complication further experiments have been carried 

 out under conditions in which the concentration of dissolved gases was 

 controlled. 



The base of the irradiation vessel was a sintered glass filter through which 

 a gas stream could be forced. This, breaking up into small bubbles, 

 ensured rapid equilibration of the solution with the desired gas, and the 

 removal of gases formed during the irradiation. Gas mixtures were pre- 

 pared by passing the individual gases through 'Rotameter' flowmeters, and 



200 



The amount o/ HoOj J 

 7 X 10«rad as a ^ ^50 



Figure 1 

 formed by 



function of the initial concentration 

 o/H,02 



JOO WO 



LL moles H2O2/ litre 



the concentrations of the dissolved gases were assumed to be proportional to 

 the partial pressures in the gas phase. 



The above experiment was repeated with this technique. It was found 

 that the hydrogen peroxide equilibrium concentration no longer depended 

 on the initial concentration. It is clear that the bubbling technique 

 removed the gaseous products of hydrogen peroxide decomposition. 



Oxygen and nitrogen^The influence of oxygen on the formation of hydrogen 

 peroxide was studied by using mixtures of oxygen and nitrogen. Each curve 

 in Figure 2 shows, the yield of hydrogen peroxide against dose for one oxygen- 

 nitrogen mixture. No hydrogen peroxide was detected with pure nitrogen. 

 Within experimental error the initial rates of formation of hydrogen peroxide 

 were independent of the oxygen concentration, whereas the equilibrium 

 values were directly proportional to the oxygen concentration. 



This result confirmed the interpretation of the experiment in which dilute 

 hydrogen peroxide solutions were irradiated at high dose rates without 

 bubbling. In these conditions, the oxygen formed by the radiolysis of 

 hydrogen peroxide determined the equilibrium values, ^\•hich were therefore 

 proportional to the initial hydrogen peroxide concentrations. 



The formation of hydrogen peroxide is usually ascribed to two distinct 

 mechanisms. If two excited water molecules are close enough together, they 

 combine directly to form hydrogen peroxide via reactions of the type A, a 



31 



