-This paper presents an experimental analysis of the effect of dose and dose rate parameters during gamma irradiation of high-density polyethylene (HDPE) samples. Considerations concerning the influence of these parameters on HDPE mechanical strength properties as a result of the predominance of oxidative degradation or of cross-linking are presented. The experimental results show an improvement of HDPE mechanical strength as dose increases, indicating the predominance of cross-linking over oxidative degradation and that lower doses are necessary to obtain a similar change in resistance parameters when radiation is applied at lower dose rates, showing that gamma radiation affects the HDPE in a more efficient way at lower dose rates.

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Dihydrate calcium sulphate (phosphogypsum) is a residue of phosphoric acid production that has been used in Brazil for agricultural purposes. However, the rate of generation of phosphogypsum is much higher than the rate of its use in agriculture and, therefore, much of this material has been stored in piles near where it is produced. This paper investigates whether the application of phosphogypsum as a material for landfill cover can contribute to an increase in exposure of humans to the natural radioactivity and toxic metals, through experimental studies (anaerobic biodegradation of the solid waste/phosphogypsum mixture) and mathematical modeling of contaminant transport in aquifers. The results indicated that application of phosphogypsum in landfill cover does not result in significant risks to either human health or the environment, for the examined conditions.

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