PNNL

Abstract

Studies have revealed that plastic scintillators can undergo environmentally related material damage that adversely affects detection performance under certain conditions and histories. A significant decrease in sensitivity has been seen in some gamma-ray detectors as they age as a result of this damage. Performance degradation due to such damage is characterized by a signal change from the detector, which shifts to lower energy, and ultimately a reduction in the ability to detect gamma radiation. Some studies have found that in extreme cold environmental conditions, significant performance loss can be observed, sometimes followed by a recovery in performance when warm conditions return. This degradation is due to the permeation of water into the plastic, which can then cause temporary fogging and permanent damage to the material. Mitigation approaches that have been proposed to prevent damage to plastic scintillator include heaters to keep the material from getting cold enough to produce damage, encapsulation of the plastic scintillator to prevent water intrusion that leads to damage during cold cycles, and new formulations of plastic scintillator. This paper presents information on testing of bare and encapsulated plastic scintillator samples and on diagnostic approaches to measure the nature and progression of the fogging condition.