Positron annihilation behavior in poly(ethylene)

The intensities and lifetimes of positrons annihilatings in low and high de nsity poly(ethylene) (LDPE and HDPE) were measured. As expected the orthopo sitronium (oPs) pick-off lifetime and intensity increases with temperature; the relative values of the intensity are consistent with differential scan ning calorimetry (DSC) results. Two other components with shorter lifetimes were deconvoluted from the complex exponential decay profiles. Detailed st udies were carried out on quenched and annealed samples of LDPE and HDPE in an attempt to correlate the two shorter components with crystallization; b oth CsF and plastic scintillators were used. DSC analyses were also carried out. We conclude that the shortest lifetime component is caused by a combi nation of parapositronium (pPs) decay and the annihilation of free positron s in the crystalline regions and that the second longest lived component ca n also be associated with crystalline regions especially the crystalline/am orphous boundary. (C) 1999 Elsevier Science Ltd. All rights reserved.