TIKVAH ALPER 



the presence of various gases or gas mixtures. As shown b)- Figure 2, the 

 survival curves were steepest with hydrogen bubbhng, and flattest with 

 hydrogen and oxygen mixtures. In the particular experiment illustrated, the 

 inactivation doses (37 per cent doses) were 900, 1,800, 3,600 and 1 l,600rads 

 for H2, N2, O2 and a H2 + Og mixture respectively. The relative yields 

 (based on the curve in nitrogen) were respectively 2, 1, 0-50, and 0-16. As 

 has been shown^, these results conform with the idea that phage particles 

 are reduced by H radicals. When the only dissolved gas present is nitrogen, 

 the free radicals formed are 



H + OH . . . . (1) 



H2O 



when h\'drogen is present, we have 



H2 + OH 



H + H2O 



(2) 



so that the probability of a phage inactivation by means of a hydrogen 

 radical, with hydrogen present, is twice that with nitrogen present. 



I 



r 



s 



4 



005 



0007 



0-07 



Figure 2. Survival curves ofSlS under various gas treatments 



It is usually agreed that, when oxygen is present in the suspension, the 

 reaction 



H + O, 



HOo 



(3) 



'2 ^ ^^'^2 • • • 



occurs. This would explain why the presence of oxygen protects the phage 

 against inactivation, at high dose rates. Nevertheless, inactivation does take 

 place, and this may be due to reduction by the radical ion 0<^^ , arising from 

 the dissociation 



HO, 



H+ +0, 



(4) 



'2 -<— ^^ ^ ^2 ... 



This possibility was supported by the results of irradiating in hydrogen and 

 oxygen mixtures, in which both HO2 and H radicals are removed by the 

 reaction 



HO2 + H -> H2O, .... (5) 



41 



