In 2010, light scattering defects were observed in several fielded panels of poly(vinyltoluene) plastic scintillators that had experienced losses in radiation sensitivity. Pacific Northwest National Laboratory first deduced that the defects were caused by trapped water. A subsequent multi-lab team funded by the DHS CWMD office found that the defects were produced when the trapped, supersaturated water caused the plastic matrix to yield. In the following years, using sophisticated optical measurements and chemical synthesis, the team discovered that the degree of light scattering and defect appearance was a function of moisture supersaturation in the plastic, scintillator formulation, and cycling history. This report focuses on the recent technical achievements by the team in 1) further understanding the root causes of the observed sensitivity loss, 2) deploying a computational tool to predict when and at which sites fogging may occur, and 3) developing and characterizing a class of fog-resistant formulations that have been demonstrated at full panel-scale and will serve as replacements for failed and at-risk panels.
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