Thermal tritium atom bombardment

The major factor limiting the attainment of high specific activities in the TA method is the low energies of the tritium atoms generated by the hot filament, about 0.3 e Particle 

This limitation in depth of labeling under TA conditions has been exploited in the study of proteins and protein assemblages, where the method is sometimes called tritium planigraphy. Such macromolecular systems, when treated under TA conditions are tritiated only in parts of molecules located at or very near the surface, leaving interior parts unlabeled. Subsequent dissection of the substrate, for example by separation of protein subunits or tryptic hydrolysis of protein followed by radioanalysis, can form the basis for inferences about the structure of the substrate. Applications of the TA method in this area include studies of the organization of the coat proteins of potato virus conformational dynamics of ribonuclease A spatial localization of coenzyme FAD in the quaternary structure of yeast alcohol dehydrogenase and subunit organization of the bacterial ribosome .  

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