Activation, nuclear recoil chemical

TTot atom radio labeling processes often leave primary products with large amounts of internal excitation. As a consequence, secondary unimolecular fragmentations can play an important, if not dominant, role in the chemical systematics of nuclear recoil activated compounds. This particular aspect of hot atom chemistry has been used to advantage by a number of workers who have applied nuclear recoil chemical activation to probe the kinetics n dyn jcs j J un q ecular rate processes (i-I5). 

In selected cases, there is a technique that can be utilized to improve the specific activity of (n,y)-produced radionuclides. This method is known as the Szilard-Chalmers process (Szilard and Chalmers 1934). The Szilard-Chalmers process depends upon the fact that, following neutron absorption, prompt y-rays are emitted, which may cause nuclear recoil and subsequent molecular bond disruption. This excitation sometimes leaves the resulting hot atom in a chemical state different from that of unreacted atoms, which makes it chemically separable. This separated fraction is relatively enriched in radioactive atoms and has a specific activity higher than that of the rest of the target. 

Pre-irradiation chemical separations followed by activation analysis are also performed for speciation studies. Speciation cannot be done after irradiation, since the chemical form can be changed due to recoil effects under the drastic conditions of nuclear reactions. This type of analysis is called chemical or molecular activation analysis (CAA). 

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