Production and validation of scintillating structural components from low-background Poly(ethylene naphthalate)

Abstract

Poly Ethylene Naphthalate (PEN) is an industrial polymer plastic which is investigated as a low background, transparent, scintillating and wavelength shifting structural material. PEN scintillates in the blue region and has excellent mechanical properties both at room and cryogenic temperatures. Thus, it is an ideal candidate for active structural components in experiments for the search of rare events like neutrinoless double-beta decay or dark matter recoils. Such optically active structures improve the identification and rejection efficiency of backgrounds events, like this improving the sensitivity of experiments. This paper reports on the production of radiopure and transparent PEN plates These structures can be used to mount germanium detectors operating in cryogenic liquids (LAr, LN). Thus, as first application PEN holders will be used to mount the Ge detectors in the Legend-200 experiment. The whole process from cleaning the raw material to testing the PEN active components under final operational conditions is reported.

Optical properties of low background PEN structural components for the Legend-200 experiment

“…In addition to being a potential background source, the structural materials also absorb the scintillation light of LAr, decreasing the background identification capabilities for events originating in the vicinity of the detectors. As part of the L R&D program, radio-pure polyethylene-naphthalate (PEN) structures have been produced using injection compression molding technology [4,5]. PEN is a commercially-available polyester, which has a yield strength higher than copper at cryogenic temperatures and therefore can be used as structural material in cryogenic physics experiments.…”

“…Scintillating low-background structures were produced by employing injection compression molding technology using commercially available PEN granulate (TN-8065 SC) from Teijin-DuPont. A detailed description of the whole process from granulate to final radio-pure and optically active support holders can be found in reference [5]. The typical support structures for the germanium detectors used in the G experiment are shown in figure 1.…”

Optical properties of low background PEN structural components for the LEGEND-200 experiment

“…Scintillating low-background structures were produced employing injection compression molding technology using commercially available PEN granulate (TN-8065 SC) from Teijin-DuPont. A detailed description of the whole process from granulate to final radio-pure active support holders can be found in reference [9]. The typical support structures for the germanium detectors used in the G experiment are shown in Figure 1.…”

“…These studies allowed to define three optimized designs to mount all types of Ge detectors used in the L -200 experiment. The final design of the low-mass PEN holders was validated during the L -200 prototyping tests at LNGS in 2020 [9,11,12].…”

“…Moreover, it can act as wavelength shifter and it scintillates in the blue region, which is ideal for most of photo-sensors devices [5][6][7][8]. In this context, a radio-pure production method has been developed and it is described in detail in reference [9].…”