PNNL

Abstract

The mass concentrations of 232Th and 238U in several strong, unfilled, high performance polymers are reported as measures of their radiopurity. Highly radiopure polymers are required as dielectric materials in the construction of rare event physics detectors, in order to minimize backgrounds arising from the detector materials themselves. New data are reported for carefully sourced samples of polyetheretherketone (PEEK), polyetherketoneketone (PEKK), a polyamide imide (PAI, branded as Torlon) and polybenzimidazole (PBI). Data for a polyetherimide (PEI, branded as Ultem) are also included from a prior study. Strong high performance polymers PEKK, PBI, PAI and PEI can be found with levels for 232Th and 238U that are below one mBq/kg. These results were all obtained using a novel dry ashing method in crucibles constructed of ultra low background electroformed copper; these low mass ULB crucibles are completely digested in acid along with the ash. Determinations were made by inductively coupled plasma mass spectrometry (ICP-MS) with liquid nebulizataion sample introduction. Radiopurity is compared graphically relative to measures of mechanical strength for these and several other polymers whose analyses have been reported previously.