Conductivity induced in Unplasticized ‘Perspex’ by X-rays

THE conductivity induced in unplasticized ‘Perspex’ (polymethylmethacrylate) by X-rays differs markedly from that induced in ordinary plasticized ‘Perspex’. First, the time-constant of recovery after irradiation is very long (several hours) for the unplasticized material, whereas for ordinary ‘Perspex’ it is much shorter1. Secondly, the equilibrium induced current i x is related to the dose-rate R by the general formula: where Δ = 0.55 ± 0.05 for unplasticized ‘Perspex’, but Δ is nearly unity for plasticized ‘Perspex’. These properties place unplasticized ‘Perspex’ in the same class of behaviour as polyethylene1,2, polytetrafluorothene3, and polystyrene4,5.