arXiv subjects

R. R. Marcelo Gregorio

Publications and source records attributed to R. R. Marcelo Gregorio.

12 recordsLinked to original sources

arXiv2026

In-situ suppression of surface radon emanation using an HDPE barrier at the Stawell Underground Physics Laboratory (SUPL)

Radon-induced backgrounds remain a limiting factor in low-background experiments conducted in underground laboratories. The enclosed nature of these laboratories can result in elevated radon levels, with emanation from the surrounding rock representing the primary source of radon. In this work, we present an in-situ study of radon emanation from the floor of the main experimental hall at the Stawell Underground Physics Laboratory (SUPL) and investigate the use of a high-density polyethylene (HDPE) barrier to suppress emanation. Surface emanation was measured using an AIRTHINGS Corentium Pro passive detector before and after installation of the barrier. The equilibrium radon concentration within the surface emanation setup was reduced from 5840 $\pm$ 50 Bq m $^{-3}$ to 259 $\pm$ 3 Bq m$^{-3}$, corresponding to a suppression of $\sim$96%. These results demonstrate the potential to retrofit radon barriers to suppress surface emanation under realistic underground conditions, supporting their use in planned low-background infrastructure at SUPL and future applications at other underground laboratories.

physics.ins-det↗

arXiv2026

Summary of quality control (QC) of ATLAS18 production ITk strip sensors

To address the demanding operational requirements of the High-Luminosity upgrade of the Large Hadron Collider (HL-LHC), the ATLAS experiment is replacing its current Inner Detector with a new all-silicon Inner Tracker (ITk). The ITk will feature an active area of 165 m2, with its outer tracking layers populated by approximately 18,000 ATLAS18 n+-in-p silicon strip sensors. The silicon sensors, available in eight geometries tailored to two barrel and six endcap types, respectively, are designed to tolerate fluences of up to 1.6 x 10^15 neq/cm2 and ionizing doses of 66 Mrad. A comprehensive, multi-year Quality Control (QC) program is underway across multiple international institutes to evaluate these ITk strip sensors for mechanical and electrical conformity. The QC process includes IV/CV characterization, full strip tests, long-term current stability monitoring, visual inspection, and metrology tests. To manage the high throughput of about 500 sensors per month, the collaboration has implemented standardized test procedures, software packages for data monitoring and integrity checks, unified data formats, and automated analysis tools. The standardization ensures consistent pass/fail evaluation and centralized data handling that enables effective identification of trends and anomalies at all sites during the production. This contribution presents an overview of the ITk strip sensor production and QC framework, along with key findings throughout the whole production, such as charge-up of sensors, stability of the leakage currents, nonrecoverable IV breakdown, and low inter-strip isolation within wafers. It provides insights into sensor yield, quality trends, and reviews specific case studies, such as p-stop doping non-uniformity. Over 91% of the production, totaling over 590 batches, were tested and accepted. Six batches were rejected. These account for 2.8% of the total tested sensors.

physics.ins-det↗

arXiv2026

High Negative Ion Gain MMThGEM-Micromegas Detector for Directional Dark Matter Searches

Low pressure gaseous Negative Ion Time Projection Chambers (NITPCs) have been used previously by the DRIFT experiment to search for a directional Dark Matter (DM) signature. The main challenge with using a Negative Ion Drift (NID) gas target is the significantly lower gas gains to which they are typically limited. Recently, a MMThGEM device has been successfully demonstrated as an excellent gain stage device in the NID gas SF$_6$; capable of producing gas gains comparable with the electron drift gas CF$_4$. The next major challenge is to extend this high gain capability to multi-dimensional readout for the purpose of particle track reconstruction. The MMThGEM is therefore ideal for coupling to a strip readout detector like a Micromegas to achieve a high gain multi-dimensional Negative Ion (NI) readout plane, which is potentially suitable for the scale up required by future searches proposed by the CYGNUS consortium. In this paper, the first high gain demonstration of such a MMThGEM-Micromegas detector in low pressure SF$_6$ is described. This includes detector characterisation in a small test vessel resulting in the largest NI gas gain ever reported, 1.22 $\pm$ 0.08 $\times$ 10$^5$ , and directionality with alpha particles. Finally, this gain characterisation and tracking capability is leveraged to measure the energy and range of events, and identify those consistent with Nuclear Recoils (NRs), in a large cubic metre scale volume of SF$_6$ for the first time.

physics.ins-det↗

arXiv2026

Direct in-chamber radon-220 (thoron) emanation measurements for rare-event physics experiments

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 the 222Rn isotope, the dominant radon isotope for these backgrounds. However, measurements of 220Rn (thoron), the second most abundant radon isotope, remain relatively unexplored. 220Rn emanation measurements are challenging because the 220Rn 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 measuring 220Rn 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 measured 220Rn emanation from low-activity thoriated rods with an activity of 76 +/- 20 mBq. Compared with a conventional flowthrough 220Rn 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-chamber 220Rn emanation measurements provide an effective tool for low-background experiments and have the potential to accelerate radon studies by exploiting the shorter half-life of 220Rn.

physics.ins-det↗

arXiv2024

Charge Amplification in Low Pressure CF4:SF6:He Mixtures with a Multi-Mesh ThGEM for Directional Dark Matter Searches

The CYGNO collaboration is developing next generation directional Dark Matter (DM) detection experiments, using gaseous Time Projection Chambers (TPCs), as a robust method for identifying Weakly Interacting Massive Particles (WIMPs) below the Neutrino Fog. SF6 is potentially ideal for this since it provides a high fluorine content, enhancing sensitivity to spin-dependent interactions and, as a Negative Ion Drift (NID) gas, reduces charge diffusion leading to improved positional resolution. CF4, although not a NID gas, has also been identified as a favourable gas target as it provides a scintillation signal which can be used for a complimentary light/charge readout approach. These gases can operate at low pressures to elongate Nuclear Recoil (NR) tracks and facilitate directional measurements. In principle, He could be added to low pressure SF6/CF4 without significant detriment to the length of 16S, 12C, and 19F recoils. This would improve the target mass, sensitivity to lower WIMP masses, and offer the possibility of atmospheric operation; potentially reducing the cost of a containment vessel. In this article, we present gas gain and energy resolution measurements, taken with a Multi-Mesh Thick Gaseous Electron Multiplier (MMThGEM), in low pressure SF6 and CF4:SF6 mixtures following the addition of He. We find that the CF4:SF6:He mixtures tested were able to produce gas gains on the order of 10^4 up to a total pressure of 100 Torr. These results demonstrate an order of magnitude improvement in charge amplification in NID gas mixtures with a He component.

physics.ins-det↗

arXiv2024

Charge Amplification in Sub-atmospheric CF4:He Mixtures for Directional Dark Matter Searches

Low pressure gaseous Time Projection Chambers (TPCs) are a viable technology for directional Dark Matter (DM) searches and have the potential for exploring the parameter space below the neutrino fog. Gases like CF4 are advantageous because they contain flourine which is predicted to have heightened elastic scattering rates with a possible Weakly Interacting Massive Particle (WIMP) DM candidate. The low pressure of CF4 must be maintained, ideally lower than 100 Torr, in order to elongate potential Nuclear Recoil (NR) tracks which allows for improved directional sensitivity and NR/Electron Recoil (ER) discrimination. Recent evidence suggests that He can be added to heavier gases, like CF4, without significantly affecting the length of 12C and 19F recoils due to its lower mass. Such addition of He has the advantage of improving sensitivity to lower mass WIMPs. Simulations can not reliably predict operational stability in these low pressure gas mixtures and thus must be demonstrated experimentally. In this paper we investigate how the addition of He to low pressure CF4 affects the gas gain and energy resolution achieved with a single Thick Gaseous Electron Multiplier (ThGEM).

physics.ins-det↗

arXiv2024

Molecular sieve vacuum swing adsorption purification and radon reduction system for gaseous dark matter and rare-event detectors

In the field of directional dark matter experiments, SF6 has emerged as an ideal target gas. A critical challenge with this gas, and with other proposed gases, is the effective removal of contaminant gases. This includes radon which produce unwanted background events, but also common pollutants such as water, oxygen, and nitrogen, which can capture ionisation electrons, resulting in loss of detector gas gain over time. We present here a novel molecular sieve (MS) based gas recycling system for the simultaneous removal of both radon and common pollutants from SF6. The apparatus has the additional benefit of minimising gas required in experiments and utilises a Vacuum Swing Adsorption (VSA) technique for continuous, long-term operation. The gas system's capabilities were tested with a 100 L low-pressure SF6 Time Projection Chamber (TPC) detector. For the first time, we present a newly developed low-radioactive MS type 5A. This material was found to emanate radon at 98% less per radon captured compared to commercial counterparts, the lowest known MS emanation at the time of writing. Consequently, the radon activity in the TPC detector was reduced, with an upper limit of less than 7.2 mBq at a 95% confidence level (C.L.). Incorporation of MS types 3A and 4A to absorb common pollutants was found successfully to mitigate against gain deterioration while recycling the target gas.

physics.ins-det↗

arXiv2023

Gas Gains Over 10$^4$ and Optimisation using $^{55}$Fe X-rays in Low Pressure SF$_6$ with a Novel Multi-Mesh ThGEM for Directional Dark Matter Searches

The Negative Ion Drift (NID) gas SF$_6$ has favourable properties for track reconstruction in directional Dark Matter (DM) searches utilising low pressure gaseous Time Projection Chambers (TPCs). However, the electronegative nature of the gas means that it is more difficult to achieve significant gas gains with regular Thick Gaseous Electron Multipliers (ThGEMs). Typically, the maximum attainable gas gain in SF$_6$ and other Negative Ion (NI) gas mixtures, previously achieved with an $^{55}$Fe X-ray source or electron beam, is on the order of $10^3$; whereas electron drift gases like CF$_4$ and similar mixtures are readily capable of reaching gas gains on the order of $10^4$ or greater. In this paper, a novel two stage Multi-Mesh ThGEM (MMThGEM) structure is presented. The MMThGEM was used to amplify charge liberated by an $^{55}$Fe X-ray source in 40 Torr of SF$_6$. By expanding on previously demonstrated results, the device was pushed to its sparking limit and stable gas gains up to $\sim$50000 were observed. The device was further optimised by varying the field strengths of both the collection and transfer regions in isolation. Following this optimisation procedure, the device was able to produce a maximum stable gas gain of $\sim$90000. These results demonstrate an order of magnitude improvement in gain with the NID gas over previously reported values and ultimately benefits the sensitivity of a NITPC to low energy recoils in the context of a directional DM search.

physics.ins-det↗

arXiv2021

Improved Sensitivity of the DRIFT-IId Directional Dark Matter Experiment using Machine Learning

We demonstrate a new type of analysis for the DRIFT-IId directional dark matter detector using a machine learning algorithm called a Random Forest Classifier. The analysis labels events as signal or background based on a series of selection parameters, rather than solely applying hard cuts. The analysis efficiency is shown to be comparable to our previous result at high energy but with increased efficiency at lower energies. This leads to a projected sensitivity enhancement of one order of magnitude below a WIMP mass of 15 GeV c$^{-2}$ and a projected sensitivity limit that reaches down to a WIMP mass of 9 GeV c$^{-2}$, which is a first for a directionally sensitive dark matter detector.

astro-ph.IM↗

arXiv2021

Test of low radioactive molecular sieves for radon filtration in SF6 gas-based rare-event physics experiments

Type 5A molecular sieves (MS) have been demonstrated to remove radon from SF$_6$ gas. This is important for ultra-sensitive SF$_6$ gas-based directional dark matter and related rare-event physics experiments, as radon can provide a source of unwanted background events. Unfortunately, commercially available sieves intrinsically emanate radon at levels not suitable for ultra-sensitive physics experiments. A method to produce a low radioactive MS has been developed in Nihon University (NU). In this work, we explore the feasibility of the NU-developed 5A type MS for use in such experiments. A comparison with a commercially available Sigma-Aldrich 5A type MS was made. The comparison was done by calculating a parameter indicating the amount of radon intrinsically emanated by the MS per unit radon captured from SF$_6$ gas. The measurements were made using a specially adapted DURRIDGE RAD7 radon detector. The NU-developed 5A MS emanated radon up to 61$\pm$9$\%$ less per radon captured (2.1$\pm$0.1)$\times 10^{-3}$, compared to the commercial Sigma-Aldrich MS (5.4$\pm$0.4)$\times 10^{-3}$, making it a better candidate for use in a radon filtration setup for future ultra-sensitive SF$_6$ gas based experiments.

physics.ins-det↗

arXiv2020

Demonstration of ThGEM-Multiwire Hybrid Charge Readout for Directional Dark Matter Searches

Sensitivities of current directional dark matter search detectors using gas time projection chambers are now constrained by target mass. A ton-scale gas TPC detector will require large charge readout areas. We present a first demonstration of a novel ThGEM-Multiwire hybrid charge readout technology which combines the robust nature and high gas gain of Thick Gaseous Electron Multipliers with lower capacitive noise of a one-plane multiwire charge readout in SF$_6$ target gas. Measurements performed with this hybrid detector show an ion drift velocity of $139~\pm~12~\text{ms}^{-1}$ in a reduced drift field $\text{E/N}$ of $93~\text{Td}~(10^{-17}~\text{V cm}^{2})$ at a gas gain of $2470\pm160$ in 20 Torr of pure SF$_\text{6}$ target gas.

physics.ins-det↗

arXiv2017

Demonstration of radon removal from SF$_6$ using molecular sieves

The gas SF$_6$ has become of interest as a negative ion drift gas for use in directional dark matter searches. However, as for other targets in such searches, it is important that radon contamination can be removed as this provides a source of unwanted background events. In this work we demonstrate for the first time filtration of radon from SF$_6$ gas by using a molecular sieve. Four types of sieves from Sigma-Aldrich were investigated, namely 3Å, 4Å, 5Å and 13X. A manufactured radon source was used for the tests. This was attached to a closed loop system in which gas was flowed through the filters and a specially adapted Durridge RAD7 radon detector. In these measurements, it was found that only the 5Å type was able to significantly reduce the radon concentration without absorbing the SF$_6$ gas. The sieve was able to reduce the initial radon concentration of 3875 $\pm$ 13 Bqm$^{-3}$ in SF$_6$ gas by 87% when cooled with dry ice. The ability of the cooled 5Å molecular sieve filter to significantly reduce radon concentration from SF$_6$ provides a promising foundation for the construction of a radon filtration setup for future ultra-sensitive SF$_6$ gas rare-event physics experiments.

physics.ins-det↗