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13 



SYNTHESIS OF ORGANIC COMPOUNDS BY 

 IONIZING RADIATION 



S. DiLLi and J. H. Green 



Department of Radiochemistry, University of New South Wales, 



Kensington, JV.S. W, 



INTRODUCTION 



The radiation synthesis of chemical compounds has begun to engage the 

 serious attention of scientists for two main reasons. Firstly, it is likely that 

 the commercial production of certain classes of compounds by radiation 

 synthesis will be economically feasible. Secondly, the synthesis of primitive 

 forms of life — from a number of amino acids, ammonia and acetic (or formic) 

 acid which could lead to a nucleoprotein — has recently become more than 

 a remote possibility. Experimental data in this field are scanty and the 

 results have not been collected together. Several accounts are available in 

 which the possibilities of radiation synthesis are mentioned in passing, for 

 example the extensive review of Collinson and Swallow^ on the radiation 

 decomposition of organic compounds and in certain bibliographies^'^a. 

 Brief comments are given in the books by Oparin^, Urey* and Bernal". 



There is no clear definition of the meaning of 'radiation synthesis'. The 

 term is used to refer generally to the formation of identifiable compounds in 

 a system which is absorbing energy from nuclear or high-energy radiation 

 sources, from sources of ultra-violet (u.v.) radiation and spark and silent 

 electric discharges. In this sense no distinction is made, on the basis of 

 physical mechanisms, between the various types of radiation and their 

 effects. If we remember, however, that several types of fragments can be 

 formed in chemical systems which are in a radiation flux, some clarification 

 is possible. 



Broadly speaking the primary reactive species in irradiated systems are 

 excited molecules and radicals and charged molecule- and radical-ions. 

 The general field of photochemistry provides information on the behaviour 

 of excited species only, because no ionization occurs in a system irradiated 

 with u.v. and visible light. The field of radiation chemistry refers to systems 

 which contain both ionized and excited species. It is in this connection that 

 we define radiation synthesis as ' the formation of radiation products, which are 

 chemically and physically different from their parents, by the combined effects of 

 ionization and molecular excitation". This definition excludes all photochemical 

 systems and leaves surprisingly few cases which can be called unambiguously 

 'radiation syntheses'. 



In earlier work in radiation chemistry, probably because the greatest 

 emphasis was put on gas-phase reactions, it was felt that the ultimate 

 behaviour of the system could be explained in terms of ion formation in 

 clusters along the radiation tracks -^ It was a relatively easy matter to 



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