Current Overshoot in Polymers under Continuous Irradiation

Abstract

An extended analysis of the conventional Rose-Fowler-Vaisberg theory shows that the product of the maximum conductivity and the time of its occurrence (yrmtm) may serve as a criterion of the validity of Langevin's mechanism of bimolecular recombination. It is proved that in PET and PS this mechanism is operative, while in LDPE it is only marginal and in PTFE its application is highly questionable. The reason offered for such a phenomenon links it with the surviving ion pairs (or tracks for densely ionizing radiation).Eine erweiterte Analyse der iiblichen Rose-Fowler-Vaisberg-Theorie zeigt, daD das Produkt aus der maximalen Leitfahigkeit und der Zeit, zu der sie auftritt (y,t,,), als Kriterium fur die Giiltigkeit des Langevin-Mechanismus bimolekularer Rekombination dienen kann. Es wird bewiesen, daB in PET und PS dieser Mechanismus wirksam ist, wahrend er in LDPE nur eine Randerscheinung und in PTFE hochst fragwiirdig ist. Die Griinde fur diese Erscheinung verbinden sie mit iiberlebenden Ionenpaaren (oder Spuren stark ionisierender Strahlung).

Langevin‐Type Charge Carrier Recombination in a Disordered Hopping System

“…Recall that previous work on charge transport in such systems, both experimental [3,4] and theoretical [5, Einstein's relation at electric fields exceeding lo5 V cm-'. It has also been conjectured [7] that charge recombination in a polymeric system deviates from the prediction of the Langevin formalism.…”

Investigation on the radiation induced conductivity of space-applied polyimide under cyclic electron irradiation

“…Afterwards, the RIC maximum for the cyclic irradiations will decrease with cycles and then down to the similar RIC levels during the long-time continuous irradiations. This phenomenon was thought to be similar to the ''overshoot'' characteristics of RIC detected in some other polymers under irradiations as reported in [21]. This RIC characteristic of polyimide under cyclic irradiations could be also defined as PIDE.…”

“…This was verified by the afterwards experimental results in various polymers [18][19][20][21]. Generally, there appear three stages in the RIC dynamical curves of amorphous polymers versus radiation time [18]: firstly in the initially short time (in a few or a few tens of nanoseconds) irradiation, the RIC of polymers increases drastically [20]; afterwards, the RIC increases slowly to a maximum [19,21]. Finally, the RIC would keep at the maximum or decrease gradually to a stable value.…”

Electron-beam charging of poly(methyl methacrylate)

“…Commercial PMMA samples always contain traces of the monomer [16]; therefore, the polymer preparation process may noticeably affect its RIC [17]. This is the reason behind the overestimated value of ∆ = 1.0 in PMMA films prepared under laboratory conditions ( P = 1-10 4 Gy/s) [18]. According to these studies, RIC in PMMA reaches its steady-state value immediately after beginning of irradiation.…”