In a former life, I worked 13 years in Nuclear Effects engineering for a defense firm and vulnerability of plastics to various levels of radiation was a major effort, including degradation as well as enhancement of thermal and physical stability due to ionizing radiation. The Nuclear and Space Radiation Effects branch of the IEEE has a substantial library of papers on this topic. You will probably be able to do a minimal web search to find the specific info you seek. I believe Sandia (Phillips lab, etc.) has done some research on plastics and radiation. The effects depend on the type of plastic.
Examples of info: A few megarads crosslinks molecules of polyethlyene, making it stronger. The same few megarads turn teflon into powder.
The above communication represents views of the author only. No representation of The University of Texas is intended or implied.
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>From: "Guinn, Charles D"