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The investigation reported herein included the measurements of several dielectric properties of TFE-fluorocarbon (Teflon) plastics before, during, and after gamma irradiation by a cobalt-60 source.
Postirradiation measurements of dielectric constant of 32- and 125-mil specimens, irradiated to a dose of 5.7 × 10 7 r, indicated no change from the preirradiation values. Dielectric strengths of 3-, 5-, and 11-mil specimens, irradiated to a dose of 5.7 × 10 7 r, did not change significantly from the preirradiation values.
Volume resistivity of specimens irradiated at dose rates ranging from 3 × 10- 2 r per hr to 1.85 × 10 5 r per hr decreased very rapidly during irradiation. After approximately 20 hr resistivity reached a constant value which was at least a factor of 10 3 below the preirradiation value. Results indicate that the resistivity during irradiation is an inverse function of dose rate and specimen thickness.
After the removal of -4- and 8-mil specimens from the irradiation field, resistivity increased steadily toward the preirradiation value. The postirradiation resistivity of 250-mil specimens increased exponentially for approximately 8 hr after which a gradual decrease was observed for several hundred hours. Post irradiation values of resistivity indicate a dependence on the dose to which a specimen was irradiated.
The Martin Co., Baltimore, Md.