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Abstract:

Measuring radon emanation from detector materials is a key method for controlling radon, a significant background in rare-event physics experiments. Methods for measuring radon emanation are well-established but have predominantly focused on the²²²Rn isotope, the dominant radon isotope for these backgrounds. However, measurements of²²⁰Rn (thoron), the second most abundant radon isotope, remain relatively unexplored.²²⁰Rn emanation measurements are challenging because the²²⁰Rn must be transferred from the emanation chamber to the active detector within its short 55 s half-life. In this study, a direct in-chamber approach for measuring²²⁰Rn emanation is presented in which the sample is placed directly within the active detector chamber, thereby minimising losses during transfer. The method was demonstrated with a DURRIDGE RAD8 electrostatic radon detector, which measured²²⁰Rn emanation from low-activity thoriated rods with an activity of 76 ± 20 mBq. Compared with a conventional flowthrough²²⁰Rn emanation setup, the in-chamber method increased sensitivity by a factor of 3. Using helium as the carrier gas provided a further sensitivity increase, giving an overall sensitivity gain of ∼ 5. These results indicate that in-chamber²²⁰Rn emanation measurements provide an effective tool for low-background experiments and have the potential to accelerate radon studies by exploiting the shorter half-life of²²⁰Rn.

Abstract:

Silicon photo-multipliers (SiPMs) are state-of-the-art sensors capable of detecting a single photoelectron under cryogenic conditions, with potentially lower radioactivity than widely used photomultiplier tubes. The DarkSide-20k experiment, designed to perform direct dark matter searches using liquid argon as the target material, employs SiPM technology to detect interactions in the active detector volumes, including the central dual-phase Time Projection Chamber and the Inner and Outer Veto volumes. The vetoes are designed to discriminate against radiogenic neutron and cosmic muon backgrounds associated with the dark matter search. This paper describes the completed production and test protocols for the “Veto Tiles” (called vTiles, arrays of 24 SiPMs integrated on a printed circuit board providing the power distribution and signal amplification); 16 vTiles are grouped into “Veto Photo-Detector Units” to instrument the Inner Veto volume. Each vTile underwent detailed testing at room and cryogenic temperatures, confirming stable operation, high signal-to-noise ratio, and low radioactive contamination, demonstrating the robustness of the proposed design for cryogenic conditions. The final production yield exceeded 87%, surpassing the 80% requirement and corresponding to 1920 Veto Tiles to populate 120 Veto Photo-Detector Units, plus an additional 6% as spares.

Abstract:

Abstract The DarkSide-20k dark matter direct detection experiment will employ a $${21}\,\hbox {m}^{2}$$ 21 m 2 silicon photomultiplier (SiPM) array, instrumenting a dual-phase 50 tonnes liquid argon Time Projection Chamber (TPC). SiPMs are arranged into modular photosensors called Tiles , each integrating 24 SiPMs onto a printed circuit board (PCB) that provides signal amplification, power distribution, and a single-ended output for simplified readout. $$16$$ 16 Tiles are further grouped into Photo-Detector Units (PDUs). This paper details the production of the Tiles and the Quality Assurance and Quality Control (QA-QC) protocol established to ensure their performance and uniformity. The production and QA-QC of the Tiles are carried out at Nuova Officina Assergi (NOA), an ISO-6 clean room facility at LNGS. This process includes wafer-level cryogenic characterisation, precision die attaching, wire bonding, and extensive electrical and optical validation of each Tile. The overall production yield exceeds 83.5%, matching the requirements of the DarkSide-20k production plan. These results validate the robustness of the Tile design and its suitability for operation in a cryogenic environment.

Abstract:

The current generation of cryogenic solid state detectors used in direct dark matter and CEνNS searches typically reach energy thresholds of O(10) eV for nuclear recoils. For a reliable calibration in this energy regime a method has been proposed, providing monoenergetic nuclear recoils at low energies ∼100 eV–1 keV. In this work we report on the observation of a peak at (1113.6-6.5+6.5) eV in the data of an Al2O3 crystal in CRESST-III, which was irradiated with neutrons from an AmBe calibration source. We attribute this monoenergetic peak to the radiative capture of thermal neutrons on Al27 and the subsequent deexcitation via single γ emission. We compare the measured results with the outcome of Geant4 simulations and investigate the possibility to make use of this effect for the energy calibration of Al2O3 detectors at low energies. We further investigate the possibility of a shift in the expected energy scale of this effect caused by the creation of defects in the target crystal.