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Effects of γ‐irradiation on the loss properties of dielectrics in vacuum
Author(s) -
Miles J. K.,
Newell D. M.
Publication year - 1965
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1965.070090210
Subject(s) - dielectric , irradiation , dissipation factor , materials science , dielectric loss , dissipation , loss factor , polystyrene , radiation , relaxation (psychology) , composite material , analytical chemistry (journal) , chemistry , optics , thermodynamics , chromatography , physics , optoelectronics , nuclear physics , polymer , psychology , social psychology
Dielectric constant and dissipation factor of six types of dielectrics were measured during irradiation in a Co 60 source. Tests were made at seven frequencies ranging from 100 cycles/sec. to 100 kcycles/sec. by use of the Schering bridge technique. Polystyrene and polyethylene exhibited no change in loss properties when γ‐irradiated to doses as high as 7.7 × 10 7 and 3.5 × 10 7 r, respectively. Poly(methyl methacrylate) decreased slightly in dielectric constant and was essentially unchanged in dissipation factor after 5.7 × 10 7 . TFE underwent the most drastic changes. At a very low dose (10 6 r) the dissipation factor had increased three orders of magnitude (at 100 cycles/sec.) and one order of magnitude (at 100 kcycles/sec.). After peaking, the loss factor decreased slowly. After removal of the source, the loss factor decreased more; then increased rapidly upon admission of air. Both this and the original increase in dissipation factor are indicative of a dipole with a long relaxation time, in which oxygen plays a role. FEP Teflon increased somewhat less than TFE, and the peak was not reached until a dose of 3 × 10 7 r. Very little effect was produced by the admission of air after irradiation. Dielectric constant decreased with radiation dose. The dissipation factor and dielectric constant of Rayolin N decreased with dose, until a plateau was reached. Very little effect was seen after irradiation, even upon the admission of air. The changes which took place during the radiation period were, as in the case of the other materials, greater at the lower frequencies than they were at the higher frequencies.