Abstract: 1. For observing the chemical effects of nutlear reaction "Br (γ,n) "Br in liquid bromobenzene, the nitrogen-containing compounds, such as aniline, diphenyamine, phenylhydrazine and pyridine, were used as additive respectively during irradiation. Similarly, aniline, diphenylamine, phenylhydrazine, dimethylaniline and pyridine were added in liquid fluorobenzene when reaction 19F(γ,n)18F proceeded.The curves indicating the dependence of recoil atom retention to the additive mole concentration were plotted, and each curve showed typically the general characteristics of being droped down sharply in low mole percent of additive and gradually in high mole percent.2. The relative effectiveness of additives in depressing organic retention was revealed in following order :phenylhydrazine>aniline≥dimethylaniline>diphenylamine≥pyridine.The reactivity of nitrogen lone-pair electrons which is influenced and bounded by the Pi-bond delocalization of the aromatic amine molecule, substantially determines this effectiveness order, we consider.3. Adding the inert additive benzene or toluene to fluorobenzene system, a linear dependence of retention to additive concentration was obtained.The contribution of the reactive functional group-NHNH2 of phenylhydrazine in reducing the retention chemically could be evaluated by the comparision of the benzene line with the phenylhydrazine curve.