The effect of Co-60 gamma-irradiation on aqueous solutions of poly(N-vinyl-2-pyrrolidone) (PVP) in the presence of persulfate anion has been investigated. The gelation dose of PVP and persulfate containing PVP aqueous solutions has been determined. At low concentrations of persulfate (1.00-3.50%), gelation percentages exhibited a decreasing trend by increasing persulfate content in aqueous solutions of the polymer. The gelation doses of persulfate containing polymer solutions were calculated by the Charlesby-Pinner equation. It was observed that the gelation dose values were shifted to higher values by increasing persulfate concentration in solution. The ratio of the chain scission and crosslinking yields (G(s)/G(x)) was also determined. The results showed that the G(s)/G(x) ratios were smaller than one for PVP aqueous solution system, whereas those obtained for persulfate containing PVP aqueous solutions were higher than unity. The results implied that the chain scission of polymer is more effective than crosslinking in the presence of persulfate. Mechanism of the crosslinking and/or degradation and structure property relationship of PVP and PVP/ persulfate hydrogel systems were investigated by Fourier transformation infeared and thermal analysis (differential scanning calorimetry, thermal gravimetric analysis and differential thermai analysis) methods. (C) 2004 Elsevier Ltd. All rights reserved.