Fig. 1. Structural formulas of coumarin and 7-hydroxycoumarin

Fig. 2. Fluorescence spectra of 7OHC solutions with different concentrations (a) and corresponding standard curve (452 nm) (b) (color online)

Fig. 3. Fluorescence spectra of TBP (a) and TiAP (b) aqueous solutions with different concentrations after γ-irradiation under N₂ atmosphere (color online)

Fig. 4. Concentration of 7OHC produced in TBP (a) and TiAP (b) aqueous solutions as a function of absorbed dose;G(7OHC) of TBP (c) and TiAP (d) aqueous solutions with various concentrations

Fig. 5. Mechanism of reaction between phosphates and hydroxyl radicals in aqueous solution: H abstraction or •OH addition; C_xH_y and R represent n-butyl (for TBP) or isopentyl (for TiAP)

Fig. 6. Relationship between the concentration ratio of TBP (a) and TiAP (b) to coumarin and G value ratio of 7-hydroxycoumarin