M. EBERT 



competition for H-radicals is between oxygen molecules and organic molecules. 

 It can be expected therefore that the values in Table I will be applicable to 

 biological systems only qualitatively. In fact, most of the observed oxygen 

 effects in radiation biology show increasing damage with increasing oxygen 

 tensions as long as the oxygen tension is low. For high oxygen tensions an 

 increase does not result in an increase in damage. 



SUMMARY 



{1) At low doses and moderate oxygen tensions the yield of hydrogen 

 peroxide is directly proportional to the dose. 



{2) The yield of hydrogen peroxide changes with changing oxygen 

 tension. At high doses, which give equilibrium values, the yield is directly 

 proportional to oxygen tension. At low doses, on the other hand, a small 

 change in oxygen tension leads to a large change in yield, if the oxygen 

 tension is low, but to a much smaller change if the oxygen tension is moderate 

 or high. This effect is enhanced at low pH. 



[3) At small doses the admixture of small amounts of hydrogen to 

 oxygen, or vice versa, increases the change in yield of hydrogen peroxide 

 considerably. The addition of large quantities of hydrogen does not change 

 the yield at low doses. 



The doses used in radiation chemical experiments are usually high from 

 the radiobiological point of view, and some reluctance may be felt in 

 applying the data to biological systems. It is undecided whether hydrogen 

 peroxide molecules are formed in tissue via the radical mechanisms discussed, 

 with doses used in radiobiology, and whether hydrogen peroxide can play a 

 significant part in causing radiation lesions. However, radical reactions are 

 bound to occur in irradiated tissue, and the investigations reported here 

 serve to show how much some radical reactions are influenced by variation 

 in both oxygen tension and h)'drogen ion concentration, particularly with 

 small doses and low oxygen tensions. 



ACKNOWLEDGEMENTS 



/ am greatly indebted to Miss T. Alper and Mr. P. Howard-Flanders for helpful 

 discussions during the progress of the work. 



REFERENCES 



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2 Gray, L. H. Brit. J. Radiol. 1953, 26 608. 



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* Ebert, M. and Boag, J. W. Disc. Faraday Soc. 1952, 12 189. 

 5 Allen, A. O. Rad. Res. 1954, 1 85. 



« Allen, A. O. Disc. Faraday Soc. 1952, 12 79. 



' Barb, W. G., Baxendale, J. H., George, P. and Hargra\e. Trans. Faraday 



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 8 Bray, J. J. Amer. Chem. Soc. 1938, 62 3357. 



* Weiss, J. Trans. Faraday Soc. 1953, 31 668. 



i« Ebert, M. and Alper, T. Nature, Loud. 1954, 173 987. 



11 Hochanadel, C. J. J. phys. Chem. 1952, 56 587. 



12 Alper, T. and Ebert, M. Science, 1954, 120 608. 



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