Temperature dependence of positron annihilation lifetime spectra for polyethylene: positron irradiation effects

Lifetime spectra for linear and branched polyethylene have been measured as a function of temperature. The longest lifetime, τ3, and its intensity, I3, are traced over a temperature range of 105-370 K. The lifetime decreases with decreasing temperature, and upon reheating the plot is retraced. I3 has a minimum near 265 K with considerable hysteresis in the cooling/heating cycle. At the lower temperatures the increase in I3 is attributed to source irradiation.