G. Chen et al., SPACE-CHARGE FORMATION IN GAMMA-IRRADIATED LOW-DENSITY POLYETHYLENE, IEEE transactions on dielectrics and electrical insulation, 5(1), 1998, pp. 51-57
Energetic ionizing radiation can alter the chemical structure of polym
eric materials and also may give rise to the presence of trapped charg
e within the material, the trapping characteristics of which may be in
fluenced by these radiation-induced structural alterations. In the pre
sent work, the formation of space charge in gamma-irradiated LDPE (low
-density polyethylene) was investigated using the technique of a LIPP
(laser induced pressure pulse). Specimens of LDPE, similar to 350 mu m
thick, were irradiated in a Co-60 gamma-source in room air to various
doses and the results indicate that space charge distributions are de
pendent on both dose and electric stress, including the length of time
during which the stress is applied. At low doses (less than or equal
to 10 kGy), there is a large amount of positive charge adjacent to the
cathode, leading to stress enhancement at the interface. Higher appli
ed stress serves to extend the positive charge towards the anode. At h
igh doses (greater than or equal to 50 kGy), the charge distribution i
s more complicated than that for low doses. Here there is initially ne
gative charge present adjacent to the cathode and a substantial positi
ve charge adjacent to the anode. With the passage of time, however, th
ere is a polarity change from negative to positive at the cathode and
a decrease in the density of the positive charge at the anode, with ne
gative charge in the middle of the sample.