Particle track detection and relaxation transitions in polymer

The sensitivity of polymeric track detectors is influenced by the registration temperature, i.e. the temperature of the polymer at the moment of the particle impact. Here, temperature effects on registration were considered in terms of molecular mobility and relaxation transitions. An attempt was made to find a correlation between the formation of heavy particle tracks in polypropylene (PP) and known transitions in this polymer. The track etch rate was measured as function of temperature in the range between 77 and 373 K. The obtained results were compared with radiothermoluminescence curves and thermally stimulated currents used for detecting charges in molecular mobility. It was found that the increase of the track etch rate with decreasing registration temperature seems to correlate with gamma and glass transitions. The decrease of the track etch rate at the irradiation temperatures below 130 K can be assigned to the situation when oxidation is prohibited but some structure reparation reactions still take place. The heating of irradiated PP samples at the temperatures above ca. 340 K leads to a dramatic increase of damage in heavy ion tracks which can be associated with another transition occurring in semicrystalline polyolefins.