Date of Award:

5-2013

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Physics

Committee Chair(s)

J. R. Dennison

Committee

J. R. Dennison

Committee

D. Mark Riffe

Committee

David Peak

Abstract

Radiation Induced Conductivity (RIC) is the change in conductivity of a material due to bombardment from incident high energy radiation. This study is to determine the effect of RIC and RIC's temperature dependence in polymeric dielectrics, specifically Kapton HN, Kapton E, PTFE Teflon, Tefzel, and Low Density Polyethylene (LDPE). Interest in these materials arises from applications for use in future spacecraft, specifically the James Webb Space Telescope (JWST).

One major issue in the design of JWST, as in all spacecraft, is the charging and arcing of exposed materials, resulting in fatal damage to the electronics and/or the craft itself. Particles prevalent in space environments bombard spacecraft, resulting in charge deposition. The electric field within the bombarded sample increases over time, finally resulting in a high enough potential difference to cause arcing from high potential surfaces to low potential surfaces. One possibility of avoiding such serious occurrences is charge dissipation due to the effect of RIC, σRIC.

A broad experimental program to study the RIC of polymeric dielectric materials has been performed by the Materials Physics Group at Utah State University. The project studied a set of approximately twelve materials to be used in the construction of the James Webb Space Telescope. Extensive instrumentation was designed, built, and tested. Characterization measurements were carried out at USU and three experimental runs were performed at the Idaho Accelerator Center (IAC) to measure the RIC of these materials.

RIC measurements were taken at the Idaho Accelerator Center in Pocatello, Idaho using a monoenergetic 4 MeV electron beam. Dose rates ranging from 0.01 rad/sec to 10.0 rad/sec were used. A voltage of approximately 50% of breakdown was applied across the samples, and resulting currents were measured to determine the conductivity. The change in conductivity at each dose rate was calculated and plotted on a log-log scale. Values for the kRIC and Δ material parameters were obtained from fits to the data. Data were also taken at ~113K, 219K, 234.5K, 296.5K, and 333K for temperature-dependent resistivity comparisons.

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