Effects of nuclear radiation on the electrical properties of polyethylene

Abstract

There exists at the present time a considerable body of information on the effects of radiation on the physical properties of types of organic electrical insulation which might be used in the construction of magnets required to operate in a nuclear environment. This information stems mainly from those involved in the manufacture of accelerator magnets (1), but in recent years there has been an ever-increasing interest in the insulation requirements of superconducting magnet coils for thermonuclear fusion reactors (2). There are differences in reliability requirements and especially so with toroidal-field coils. The neutron energy spectrum here will be essentially that of fast fission (3) and the ratio of absorbed dose for neutron to photon radiation will be a function of blanket and shield construction. This ratio could be around 10 : 1, and as most radiation effects studies have been made using pure gamma radiation, the question arises as to the relative effects of similar absorbed doses of neutron and photon radiation to determine how valid gamma radiation data is for fusion reactor design (4). Some results on this topic are presented here for ambient temperature conditions. The work discussed forms part of a wider programme of research into nuclear radiation effects on organic insulation over the temperature range ambient to 5K.