Effect of Carrier Traps in Polyethylene under Gamma-Ray Irradiation

Abstract

Stimulated currents are detected with increasing temperature in polyethylene films following the irradiation with high‐energy electron beams at 77°K. A peak current occurs at about 200°K in low‐density specimens and 250°K in high‐density ones. Induced currents I under gamma‐ray irradiation of polyethylene at room temperature depend on dose rate R via I ∝ R^Δ. In high‐density polyethylene preirradiation by electron beams of about 5×10⁷ rads at room temperature Δ increases from 0.5 to 0.84 and is accompanied by a decrease of induced current. In the low‐density specimens Δ decreases from 0.8 to 0.6 and the induced current increases with the same preirradiation. After boiling the preirradiated specimen for 5 min, Δ becomes 0.5 in both cases, and in the high‐density specimens the induced current I returns to that of the nonirradiated sample. This behavior suggests that the increase and decrease of carrier traps by these treatments influence the induced current characteristics. Another factor influencing the induced conductivity is the crystallinity; with decreasing crystallinity the induced conductivity of all specimens decreases, while in most cases Δ values increase. This behavior suggests the domination of electrons as charge carriers and that they are able to flow more easily in the crystalline parts than in the amorphous parts.