Temperature Dependence Study Of Positronium Formation In High Density Polyethylene By Positron Annihilation Lifetime Spectroscopy

Positron annihilation lifetime spectroscopy has been used to study the formation of positronium in high density polyethylene as a function of temperature over the range 30 K-350 K. It is observed that the thermal history of the sample, while having no influence on the positronium lifetime, has a strong effect on the formation of positronium. A hysteresis is seen in the positronium formation probability in cooling and heating cycles. This is explained on a two channel formation model, the first channel being through "blob" formation and the second through the pick-up of shallow trapped electrons. (c) 2007 WILEYNCH Verlag GmbH & Co. KGaA, Weinheim.