KINETICS OF PRIMARY REACTIONS AND CHEMICAL PROTECTION 317 



With the lowering of oxygen pressure in water irradiation, tlie 

 amount of the products of water radiolysis decreases. However the 

 kinetic curves of this i)rocess are evidently different. In this case the 

 changes in the oxidizing capacity of water give a slo])ing curve. 



The dependence from oxygen pressure of the threshold of the rate of 

 the reaction has been known in chemical kinetics and is a peculiar 

 feature of oxidizing chain reactions with branching chains. This tyj^e 

 is usual in the oxidation of lipids, as lipoperoxide compounds easily 

 arise, securing the branching of the reactions. This type of reaction is, 

 according to Semenov (1958), characterized by anomalous dependence 

 of the rate of oxidation from oxygen pressure. The breaking of chains 

 and the inhil)ition of the reactions is achieved both at low and high 

 pressures. Independently of the radiation effect the rise in oxygen 

 pressure has a toxic effect on organisms. Against the background of 

 this toxic effect it is very difficult to establish the influence of increased 

 oxygen pressure on the primary reactions. 



But that is possible for organisms for which oxygen is not toxic. In 

 our laboratory we have undertaken the study of the effect of oxygen 

 with a very wide range of pressures from to 1 1 atm on a yeast which 

 can survive in pure oxygen at any pressure. 



Studying the relationship of survival after radiation with oxygen 

 pressure, Kolontarov (1958, 1959) has discovered that not only a de- 

 crease but an increase of oxygen pressure as well has a protective effect 

 (Fig. 2). 



o 

 o 



0-2 0-6 1-0 



Oxygen tension (atm) 



Fig. 2. 



]-4 



In no connection with our work, a paper has recently been published 

 by Alper (1959) in which it is stated that irradiation of the yeast Saccha- 

 romyces vini in an atmosphere of ]5ure oxygen increases its capacity 



