Measurement of the absolute reflectance of polytetrafluoroethylene (PTFE) immersed in liquid xenon

Abstract

The performance of a detector using liquid xenon (LXe) as a scintillator is strongly dependent on the collection efficiency for xenon scintillation light, which in turn is critically dependent on the reflectance of the surfaces that surround the active volume. To improve the light collection in such detectors the active volume is usually surrounded by polytetrafluoroethylene (PTFE) reflector panels, used due to its very high reflectance -even at the short wavelength of scintillation light of LXe (peaked at 178 nm). In this work, which contributed to the overall R&D effort towards the LUX-ZEPLIN (LZ) experiment, we present experimental results for the absolute reflectance of three different PTFE samples (including the material used in the LUX detector) immersed in LXe for its scintillation light. The obtained results show that very high bi-hemispherical reflectance values (≥ 97%) can be achieved, enabling very low energy thresholds in liquid xenon scintillator-based detectors.

Liquid xenon scintillation measurements and pulse shape discrimination in the LUX dark matter detector

“…Each end of the TPC is instrumented with an array of 61 Hamamatsu R8778 photomultipler tubes (PMTs) to detect light signals generated in the TPC. Twelve polytetrafluoroethylene panels, >95% reflective at 175 nm [26], line the walls to increase the light collection efficiency. The scintillation signal, denoted S1, is detected directly by the PMTs.…”

Measurements of angle-resolved reflectivity of PTFE in liquid xenon with IBEX

“…Fluorescence of the PTFE in the visible, due to impurities, has been observed in prior work [33,34,30] and may differ between this and other setups. In particular, an enclosed PTFE geometry such as those in [10,7] may enhance fluorescence effects [35,36].…”

“…Some powder materials were chosen for direct comparison with the results of total reflectance measurements in LXe from [10], including 807NX and NXT85 from Applied Plastics Technology and a sample of the material used in the LUX detector [1], molded 8764 PTFE from Technetics of an unknown powder material. These materials were found to have an estimated total reflectivity of >95% [10,7]. Other samples were made from M17 and M18 PTFE powder from Daikin.…”

“…These results are based on simulations assuming reflection is purely diffuse, and exhibit degeneracies with other parameters such as attenuation length in the LXe. A dedicated experiment designed to measure total PTFE reflectivity in LXe found values in excess of 95% across several PTFE types [10]. Though some of these PTFE surfaces show signs of deviation from purely diffuse reflection, the experiment referenced is unable to directly measure the angular distribution of the reflected light.…”

Liquid xenon in nuclear medicine: state-of-the-art and the PETALO approach

“…At the liquefaction temperature of xenon, SiPMs can be operated without problems, and their dark count rate is essentially negligible. In its simplest version, each cell has the entry and the exit faces instrumented, while the others are covered with a highly reflective material such as PTFE, which features close to 100% reflective efficiency at UV wavelenghts [23]. The shape and the dimensions of the box itself can be adapted to the specific application, as well as the density of SiPMs on each face.…”