Luminescence from γ-irradiated humic acid

This study was conducted to investigate the ultraweak delayed radiochemiluminescence (RCL) spectra, kinetics and spectroscopic properties of humic acids (HAs) after γ-radiation exposure (absorbed doses of 1−10 kGy, Co-60) in model systems. The kinetics and spectral distribution of RCL (340–650 nm) were measured using the single photon counting (SPC) method and cut-off filters. The intensity of fluorescence (λex=390, 440, 490 and 540 nm) covering the spectral range 400–580 nm was heavily dependent on the λex and slightly increased with the absorbed dose of γ-radiation. Absorption spectra (the range 240−800 nm) and color coefficients E2.6/4 and E4/6 of irradiated solutions indicated that post-radiative degradation/polymerization processes take place in the HA, changing their macromolecule size or properties. Comparison of FTIR spectra and elemental analysis proved an increased O and decreased C atoms in irradiated samples. The data indicate on the radiolysis-induced degradation of native HA into fulvic-like acids with higher hydrophilicity and lower molecular size.