Low Radioactivity Techniques (LRT2022)

Jun 14, 2022, 7:25 AM → Jun 17, 2022, 5:55 PM US/Mountain

EEP 252 (South Dakota Mines)

Jaret Heise (Sanford Underground Research Facility), Richard Schnee (SD Mines)

LRT 2022, Co-hosted by South Dakota Mines and the Sanford Underground Research Facility (SURF)

The Low Radioactivity Techniques (LRT) workshop series examines topics in low-radioactivity materials and techniques that are fundamental for quantum information science and rare-event searches, including dark matter, solar neutrinos, double-beta decay, long half-life phenomena and nuclear astrophysics.

The workshop features updates from underground laboratories around the globe as well as the latest information regarding all aspects of low background detectors, techniques and assay programs in addition to recent developments in advanced machining and 3D printing using ultra-pure materials.

The goal of this workshop series is to bring together experts in this field for presentations and discussion broadly covering topics related to low radioactivity techniques. The intention is to foster and continue the collaboration and resource sharing required for new generations of detectors to be developed at underground facilities.

The workshop is being hosted in the Black Hills of South Dakota at SD Mines in Rapid City, near SURF which is the deepest underground laboratory in the United States. The area’s natural beauty attracts tourists year-round, and has strong connections to Native American culture and history.

Initiated by the Sudbury Neutrino Observatory in 2004, the 2022 meeting is the 8th international topical workshop in the LRT series:

• LRT2019 hosted by the Laboratorio Subterráneo de Canfranc (LSC) in Jaca, Spain
• LRT2017 hosted jointly by the Institute for Basic Science (IBS) Center for Underground Physics (CUP) and Ewha Womans University in Seoul, South Korea
• LRT2015 hosted jointly by PNNL and the University of Washington in Seattle, USA
• LRT2013 hosted by Laboratori Nazionali del Gran Sasso (LNGS) in Assergi, Italy
• LRT2010 hosted by SNOLAB in Sudbury, Canada
• LRT2006 hosted by Laboratoire Souterrain de Modane (LSM) in Aussois, France
• LRT2004 hosted by SNO at Laurentian University in Sudbury, Canada

The workshop will follow the APS Code of Conduct.

LRT2022 Announcement #1 (Jan 26)

LRT2022 Announcement #2 (Feb 22)

LRT2022 Announcement #3 (Mar 30)

LRT2022 Announcement #4 (May 11)

LRT2022 Maps (Campus, Restaurants, Lodging)

LRT2022 Press Release

LRT2022 Workshop Poster

SD Mines General Lodging Flyer

Tuesday, June 14

7:40 AM Hotel transport - Coffee/Breakfast - Registration

LRT 2022 - presentations: Welcome / Global Underground Laboratories

Convener: Sean Paling (Professor at Boulby Underground Laboratory in UK)

1 Welcome

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Speakers: Jaret Heise, Dr Ralph Davis (South Dakota Mines), Richard Schnee

LRT2022 Welcome.pdf

2 Stanley Howard Lecture

Remembrance of late Stanley Howard, SD Mines professor in the Department of Materials and Metallurgical Engineering

Speaker: Jon Kellar

Stan Homage.pptx

3 Underground Facilities - Americas

Updates from underground laboratories in North & South America will be presented, with a focus on progress at the Sanford Underground Research Facility (SURF).

Speaker: Jaret Heise

Heise - UG Labs Americas - LRT2022 - 2022_06_14-Rev1.pdf

4 Overview and Status of Underground Labs in Asia

Deep underground laboratories in Asia continue to add locations, size, and facilities to support current and next generation rare-event experiments related to neutrino physics, nuclear astrophysics, searches for dark matter and neutrinoless double beta decay, and other science requiring low-background environments. I will present an overview and status of major underground labs in Asia including the Jiangmen Underground Neutrino Observatory (JUNO) and the China Jinping Underground Laboratory (CJPL), both in China, the India-based Neutrino Observatory (INO) in India, the Yangyang Underground Laboratory (Y2L) and the newer Yemilab in South Korea, and the multiple underground facilities in Kamioka in Japan.

Speaker: Dr Douglas S. Leonard (IBS Center for Underground Physics)

Leonard-Asian-Labs-Overview-LRT-2022.pdf

10:10 AM Coffee / Refreshments

LRT 2022 - presentations: Global Underground Laboratories / Screening Facilities

Convener: Richard Ford (SNOLAB)

5 Underground Facilities - Europe

Updates on underground laboratories in Europe will be presented, with a focus on the Boulby Underground Laboratory

Speaker: Sean Paling

LRT2022_Boulby_2022.pdf

6 Confronting the radiological screening challenges for next-generation rare event detectors

Over the past few decades, the scale and mass of rare event search experiments have increased by several orders of magnitude. To maintain background-free large fiducial-volume searches, the radio-purity requirements of the materials from which these devices are constructed have improved by similar factors.
High-purity germanium spectroscopy has long-been the workhorse of material screening and selection, providing information on trace radioactive gamma-ray emitting impurities in the bulk of materials. The next generation of direct dark matter and neutrinoless double beta decay experiments demand the development of additional assay techniques to provide a more complete understanding of the full uranium (U) and thorium (Th) decay chains, including knowledge of alpha-emitting surface depositions.
In this talk I will highlight the challenging radiopurity requirements for the next generation of rare event search experiments, as well as the extensive UK-based material assay infrastructure in place to address these demands. Where requirements exceed current capability, additional R&D is needed. I will summarise where this R&D is already underway across the UK.

Speaker: XinRan Liu (The University of Edinburgh)

LRT2022_XRL.pptx

7 Counting Facilities at the Black Hills Underground Campus (BHUC)

The Black Hills Underground Campus (BHUC) houses a low background counting facility on the 4850’ level of the Sanford Underground Research Facility. Currently there are five ultra-low background, high-purity germanium detectors operating inside of a class 1,000 cleanroom at the Davis Campus, with a sixth anticipated to be installed within a year. A robust nitrogen purge system and on-site personnel assistance allow these detectors to run continuously to support groups that need low background counting of materials.

Speaker: Doug Tiedt (Sanford Lab)

BHUC_SURF_LRT_2022.pdf

12:10 PM Lunch - Grab'n Go

Excursions: SURF visit / Badlands tourist excursion / Custer tourist excursion

Wednesday, June 15

7:40 AM Hotel transport - Coffee/Breakfast

LRT 2022 - presentations: Fabrication Methods

Convener: Alvine Kamaha (University of California, Los Angeles)

8 Additive manufacturing techniques for producing low-background scintillators and materials for rare-event searches

Reducing radioactive backgrounds is key for the success of many rare-event searches such as neutrinoless double beta decay, dark matter, and nuclear astrophysics. For a given component used in a rare-event search, backgrounds may be due to intrinsic radiocontaminants within the material and radiocontaminants that are introduced during manufacturing. Advances in additive manufacturing techniques, such as 3D printing, provide attractive solutions for mitigating radiocontamination as well as enabling new geometries and multi-material compositions to be produced. These geometries would otherwise be near impossible to cleanly produce using conventional techniques. These advances apply not only to inactive materials but also active ones such as scintillators, which provide a powerful discrimination tool in rejecting internal and external background. In this talk, I will provide an overview of 3D printing techniques which may find future applications in rare-event searches. In addition, an overview of current R&D status of light-based 3D printing of low-background and scintillating materials will be discussed.

Speaker: Michael Febbraro (ORNL Physics Division)

LRT2022_febbraro.pdf

9 Additive Manufacturing at LNGS: Facilities, Metals Testing and Future Capabilities

Selective laser melting (SLM) method occupies a special place in powder bed fusion (PBF) technology. The growing widespread interest in this technique is due to its several benefits. The final near to net-shape product, which has up to 99.9% relative density is the key advantage and with the extensive applicable materials, PBF–SLM has feasible economic benefits. This talk covers all the aspects of SLM technology development at Gran Sasso National Laboratory, stressing the attention on the product lifecycle management of complex components, their design for additive and engineering optimisation, the geometry and surface quality analysis, the relative materials processed and the actual and near future capabilities for science and industry purposes aboveground and underground. Research works on real operative components made of Copper OFE, Copper Alloys, Aluminum Alloys and Stainless Steel are presented.

Speaker: Donato Orlandi

Donato_Orlandi_LRT2022.pdf

10 Update on Electroforming Plans and Facilities

As the background level of new detector systems is pushed ever lower the demand for radiopure materials continues to increase. Electroformed copper is playing an ever more central role in many experiments. That is due to its favorable electrical and thermal properties in addition to the extremely high radiopurity levels that can be obtained using electroformed copper leaving room in their experimental background budgets for the more radiopurity challenged materials. We will discuss the use of electroformed copper in a few of these planned experiments and the electroforming facilities that are supporting them.

Speaker: E. W. Hoppe (PNNL)

LRT-2022-Electroforming Hoppe.pdf

11 Ultra-low background flexible cables

Readout cables for signal sensors are a fundamental component of rare event searches for dark matter and neutrinoless double beta decay. While possessing unique electrical and mechanical properties, polyimide-based flexible cables can be a significant contributor to the total detector background, due to their relatively high content of natural radionuclides. Contaminations of 232Th and 238U in commercially-available flexible cables have been measured in the mBq/kg range, making them incompatible with the stringent levels required for next-generation rare event detectors.
In previous work, we have demonstrated the possibility of obtaining low-background (µBq/kg) copper-polyimide laminates which serve as the starting material for flexible cable manufacturing. However, we have found that even when starting with low-background laminates, the cable manufacturing process results in finished flexible cables with high (mBq/kg) levels of radioactivity.
In this work, each step of the flexible cable manufacturing process was systematically investigated using inductively coupled plasma mass spectrometry as a potential vector of radioactive impurities. Through the investigation of process modifications, the development of cleaning procedures, and surveys of alternative materials, we have demonstrated that the radioactivity content from 232Th and 238U can be reduced to a few tens of µBq/kg. We will discuss our key findings, report the current best levels of radiopurity achieved, and discuss future plans for making ultra-low background flexible cables commercially available.

Speaker: Richard Saldanha (PNNL)

Saldanha_Clean_Cables_LRT2022.pdf

10:00 AM Coffee / Refreshments

LRT 2022 - presentations: Particle Background impacts on Quantum Information Systems and Quantum Computing

Convener: Brianna Mount

12 The Interplay of Radioactivity and Quantum Science

The presence of nonequilibrium quasiparticles (QPs) hinders the performance of superconducting qubits. This excess of nonequilibrium quasiparticles arise mainly from two primary sources: in the infrared photons that couple to qubits via photon-assisted quasiparticle generation, and the impact events in which ionizing radiation deposits large amounts of energy (keV) onto the qubit chip. The latter results in spatiotemporally-correlated errors that challenge quantum error correction schemes. My talk will review the current knowledge status of the effect of ionizing radiation on qubit coherence, and how various methods (from on-chip mitigation to underground shielding) can be used to help mitigate the obstacles imposed by such radiation.

Speaker: Joseph Formaggio

Low_Radiation_Techniques_2022-4.pdf

13 Backgrounds in Qubits

Quantum devices and light dark matter searches are scientifically active fields. I will discuss the complementarity in technology and research between these two fields. I will discuss recent observations of ionizing radiation backgrounds in leading quantum processors and the insights that can be gained from dark matter searches based on low temperature calorimetry. Extending this observation, environmental sources at low energies interfere with superconducting device performance, and understanding these sources in light dark matter experiments will improve the performance of low temperature superconducting devices. Finally, I will discuss the underground infrastructure involved in this research.

Speaker: Jeter Hall

LRT_quantum_backgtounds_Hall.pdf

14 Quantum Sensors for Direct Detection of Sub-GeV Dark Matter

Over the last 20 years, searches for dark matter above the proton mass have advanced significantly across direct and indirect searches, but sub-GeV dark matter has until recently been comparatively unprobed. In this talk, I will discuss prospects for applying quantum measurement techniques to lowering mass thresholds for new searches with event thresholds at the eV-scale. I will then discuss synergies with ongoing research in materials science and quantum information science. The goal over the next decade is to run background-free dark matter searches at gram-year exposures with meV-scale thresholds, an exciting challenge that requires a broad range of expertise, and comes with enormous scientific discovery potential.

Speaker: Noah Kurinsky

LRTTalk.pdf

15 From signal to noise -- athermal phonon mitigation in quantum devices

Athermal phonons are high-energy vibration modes in solid-state substrates. They are the signal channel for sub-GeV low-mass dark matter direct search, while they are also dangerous noises in quantum information systems. I'll first introduce the method of athermal phonon detection in particle detectors. Then I'll discuss three approaches to mitigate athermal phonons: isolation, down-conversion, and phonon cloaking, inspired by particle and cosmology microwave background detectors.

Speaker: XinRan Li

LRT2022.pdf

16 Impact of environmental and materials radioactive contamination in superconducting quantum bits

Radioactivity was recently discovered as one of the main concerns for quantum processors based on superconducting circuits. Cosmic rays and radioactive isotopes naturally present in the environment can affect the coherence time of single qubits and induce correlated errors in qubit arrays, seriously affecting quantum error correction. We developed a GEANT-4 based simulation to study the effect of “external” sources of radioactivity (gammas, neutrons and cosmic muons), and close materials contamination (chip holder, magnetic shield, …) on a typical qubit developed within the SQMS center. We finally propose mitigation strategies.

Speaker: Giulia D'Imperio

Radioactivity_superconducting_qubits_LRT_2022.pdf

12:10 PM Lunch

LRT 2022 - presentations: Surface Contamination Control

Convener: Juergen Reichenbacher (South Dakota School of Mines and Technology)

17 Removal of long-lived radon daughters from surfaces

Surface contamination with long-lived daughters of Rn-222 is of great interest for experiments looking for rare events. These include for example searches for neutrino-less double beta decay or interactions of dark matter particles. Decays of Pb-210, Bi-210 and finally Po-210 may contribute significantly to the experiments’ background, especially when they appear close or directly in the active volumes. Due to alpha decays of Po-210 taking place on surfaces (and thin sub-surface layers) neutrons can also be produced. They may be a serious background source in dark matter detectors since they interactions are difficult to distinguish form dark matter particles. Measurements of natural surface contamination with Po-210 of various samples will be presented. Measurements were performed with an ultra-low background, large-area alpha spectrometer. The instrument allows to study the surface contamination down to about 0.5 mBq/m2. From the registered spectra one can also deduce the Po-210 bulk contamination down to 30 mBq/kg. Contaminated surfaces were also cleaned, in case of metals etching and/or electro-polishing was applied to study the effect of Po removal. For example for copper electro-polishing was always effective and provided high Po activity reduction factors. Standard etching procedures are in general less effective, therefore a fast multi-step process has been developed where one longer bath is replaced by several subsequent and short runs always with fresh etchant. Application of the new procedure to various copper samples resulted in Po activity reduction by more than two orders of magnitude, down to the detection limit of the instrument. Other surfaces, like stainless steel, germanium or lead will be discussed together with the applied cleaning protocols as well.

Speaker: Grzegorz Zuzel

Zuzel_LRT_2022.pdf

18 Simulation studies on radon daughter plateout background in nEXO

nEXO is a proposed search for neutrinoless double beta decay of $^{136}$Xe. The experiment is planning to utilize isotopically enriched xenon both as source and detection medium. Radon daughters produced by radon decays in the air can plate out on material surfaces during detector assembly and handling. The alpha particles they emit can interact with low-Z materials nearby and produce fast neutrons. These neutrons can in turn produce $^{137}$Xe when captured by $^{136}$Xe, contained in the nEXO detector medium. The subsequent beta decay of $^{137}$Xe (Q = 4173 keV) can mimic $0\nu\beta\beta$ in nEXO. In this talk, I will describe simulation studies performed to estimate the background in nEXO produced by radon daughters. I will also discuss the allowed amounts of radon daughters on material surfaces in order to meet nEXO's stringent background requirements.

Speaker: Hei Man (Raymond) Tsang (University of Alabama)

tsang-lrt2022-nexo-alphan.pdf

19 Radon daughter plate-out as a background source in nEXO experiment

nEXO is a planned next-generation experiment to search for $^{136}$Xe neutrinoless double beta decay. The experiment will utilize a time projection chamber and 5000 kg of isotopically enriched liquid xenon. The projected 90% CL half-life sensitivity is 1.35·10$^{28}$ yr after 10 yr of exposure. Stringent radioactive background control and careful material selection are necessary to achieve such sensitivity.
Radon daughter plate-out is one source of background in the nEXO experiment. The exposure of detector materials to air will lead to the accumulation of $^{210}$Po, whose α-decay can produce neutrons from (α, n) reactions. Some of these neutrons will capture on $^{136}$Xe to form $^{137}$Xe, whose β-decay will create background events. A literature survey gives a wide range of measured radon daughter attachment lengths. To understand the reasons of such variability the nEXO group at the University of Alabama conducted a measurement campaign using various materials relevant for nEXO. The campaign included measurements in several environmental conditions with careful monitoring and control of the exposure parameters. Results are compared to the Jacobi model.

Speaker: Dmitry Chernyak

2022_LRT_Presentation_DChernyak.pptx

20 Development of an ultralow-background bolometric alpha detector for the measurement of surface contamination

Next-generation experiments searching for rare events must satisfy increasingly stringent requirements on the bulk and surface radioactive contamination of their active and structural materials. The measurement of surface contamination is particularly challenging, as no existing technology is capable of separately measuring those parts of the 232Th and 238U decay chains that are commonly found to be out of secular equilibrium.
We will present the results obtained with a detector prototype consisting of 8 silicon wafers of 150mm diameter instrumented as bolometers and operated in a low-background dilution refrigerator at the Gran Sasso Underground Laboratory of INFN, Italy.
The prototype was characterized by a baseline energy resolution of few keV and a background of ~60 nBq/cm2 in the full alpha range, obtained with simple procedures for the cleaning of all employed materials and no specific measures to prevent recontamination. Such performances, together with the modularity of the detector design, demonstrate the possibility to realize an alpha detector capable of separately measuring all alpha emitters of the 232Th and 238U chains, possibly reaching a sensitivity of few nBq/cm2.

Speaker: Mr Giovanni Benato (Laboratori Nazionali del Gran Sasso - INFN)

GiovanniBenato_LRT2022.pdf

21 Exploration of Methods to Remove Implanted Pb-210 and Po-210 Contamination from Silicon Surfaces

The relatively long-lived Pb-210 (half-life of 22 years) and its progeny can be problematic sources of background for rare-event physics experiments. Pb-210 can be present in the bulk of materials at detrimental levels and concentrated at the surfaces of detector components as a result of exposure to environmental radon, where its decay products (and those of its progeny such as Po-210) can cause background issues on or near active detector targets. This talk will present on a variety of mitigation techniques to remove implanted 210Pb and 210Po from silicon surfaces. Both chemical and physical methods were explored which ranged in efficacy, with some of the most promising approaches allowing for the near complete removal of Pb-210 and Po-210. Approaches may be implementable during different phases of detector construction of silicon devices in order to remove Pb-210 and Po-210, and/or provide avenues for mitigation techniques for removal of Pb-210 and Po-210 from other detector materials.

Speaker: Dr Isaac Arnquist (Pacific Northwest National Laboratory)

Arnquist_LRT2022_final.pptx

LRT 2022 - poster session: + Coffee / Refreshments

22 The Cold Radon Emanation Facility

Radon emanation from construction materials has emerged as a dominant background to current and next generation dark matter searches, particularly those deploying noble liquid targets where radon progeny is expected to decay uniformly across fiducial volumes. Sensitivity studies show that radon activities of ~0.1uBq/kg must be achieved in order to probe the remaining parameter space accessible to standard intermediate mass WIMPs. Some fraction of radon may be removed from targets through purification and there is also potential to identify radon events in xenon target analysis, the latter of which will be discussed in this talk. However, the most direct mitigation at present is to screen potential construction materials for radon emanation directly.

Radon emanation assays of materials are typically performed at room temperature, resulting in large uncertainties when translating screening results to expected rates in noble liquid targets due to the cold suppression of radon diffusion within and subsequent emanation out of materials. Accurately predicting radon emanation from materials in experiments therefore requires assays at final operating temperatures.

The Cold Radon Emanation Facility (CREF), currently being commissioned at RAL, is designed to perform radon emanation studies of materials with sufficient sensitivity and at temperatures of relevance for the construction phases of next generation rare-event searches. It inherits heavily from existing radon emanation assay systems, such as those deployed for the LZ and SuperNEMO projects, to deliver a world-leading sensitivity below 0.1 uBq/kg to 222Rn emanated from materials at room temperature into dedicated emanation chambers. Additionally, CREF is designed to be operated with the emanation chambers cooled to LAr or LN2 temperatures for low-temperature assays. Finally, CREF incorporates a large 200 L litre chamber, operating within a 500 L cryogenic vessel, that can be cooled and stabilised at temperatures down to ~77 K. This allows measurement of ‘as built’ detector components and to establish their rate of emanation as a function of temperature.

Speaker: Emily Perry (PhD Student)

23 The Radon Emanation Measurement System of PandaX-4T [remote]

Radon emanated from detector materials and their decay daughters are potentially dangerous sources of rare event search experiments. In order to measure and control emanated radon for PandaX-4T detector, a radon emanation measurement system with electrostatic collection technique was designed. This system is consisting of a hemispherical copper counting chamber, a spiral cold trap and an acrylic emanation chamber. The hemispherical shape improves the collection efficiency of radon daughters to 27.75 ± 0.01 % , and the blank rate of copper chamber is 0.54 ± 0.09 mBq. The cold trap at the liquid nitrogen temperature enriches radon to improves the detection efficiency by factor of 20. The acrylic emanation chamber has no significant contribution to the background of the whole system. Furthermore we will polish the surfaces of the counting chamber and the emanation chamber to suppress the background.

Speaker: Lin Si (School of Physics and Astronomy, Shanghai Jiao Tong University, MOE Key Laboratory for Particle Astrophysics and Cosmology, Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai 200240, China)

24 Detector characterization for the LEGEND-200 experiment

The LEGEND collaboration is developing an experimental search for the neutrinoless double-beta ($0\nu\beta\beta$) decay of the isotope $^{76}$Ge. The first stage, LEGEND-200, is based on 200kg of $^{76}$Ge-enriched high-purity germanium detectors immersed in liquid argon. It is currently under construction at the Laboratori Nazionali del Gran Sasso in Italy.
Among others, novel inverted coaxial point-contact detectors provide the information to effectively discriminate against background events. Such background discrimination requires a precise understanding of the behavior of the germanium detectors, necessitating extensive detector characterization. The acceptance tests aim to verify the performance of the delivered detectors meets specifications and to determine their optimal operational parameters. Furthermore, one of the most important issues is the determination of the active volume of the detectors. It can be attained by studying the detector response when irradiated by radioactive sources.
The first results of the characterization program with an emphasis on active volumes are presented.

Speaker: Valentina Biancacci (Università degli Studi di Padova & INFN Padova)

2022-06-15-Biancacci-LRT2022.pdf

25 Science at LSM, Underground Laboratory of Modane

The Underground Laboratory of Modane (LSM, Laboratoire Souterrain de Modane) is the deepest European underground multidisciplinary platform. Under 4800 m.w.e ( Meter Water Equivalent), the LSM gives the opportunity to all experiments need to be sheltered from cosmic rays and/or looking for rare events to be hosted.
From Electronics, Biology, HPGe gamma spectrometry up to fundamental physic, in particular Dark Matter search and neutrino double beta decay, are the science objects which lives at underground laboratory of Modane.
In this talk, we’ll review of existing and coming experiments will be shown after speaking about the specification of the LSM infrastructure.

Speaker: Ali DASTGHEIBI FARD (France CNRS/LPSC_LSM)

26 R2D2: a xenon TPC for neutrinoless double beta decay search

The search for neutrinoless double beta decay could cast light on one critical piece missing in our knowledge i.e. the nature of the neutrino mass. Its observation is indeed the most sensitive experimental way to prove that neutrino is a Majorana particle. The observation of such a potentially rare process demands a detector with an excellent energy resolution, an extremely low radioactivity and a large mass of emitter isotope. Nowadays many techniques are pursued but none of them meets all the requirements at the same time. The goal of R2D2 is to prove that a spherical high pressure TPC filled with xenon gas could meet all the requirements and provide an ideal detector for the 0νββ decay search. The prototype has demonstrated an excellent resolution with argon at low pressure and test at higher pressure are ongoing. The xenon recuperation and
recirculation system is under commissioning and results in xenon will be obtained soon. In addition the light readout has been recently tested. In the proposed talk the R2D2 results obtained with the first prototype will be discussed as well as the project roadmap and future developments.

Speaker: Cedric Cerna

27 Cosmogenic activation calculation of experiments with LAr target

In rare event search experiments, activation of detector materials can lead to significant backgrounds. Typically, trace radioactive contaminants are activated by cosmic-ray interactions while the detector materials are being stored or transported above ground. In highly sensitive experiments, these cosmogenic backgrounds can limit sensitivity. It is therefore necessary to determine the cosmogenic activation of detector materials before installation. Liquid Argon (LAr) is used as a target for many future experiments, including DarkSide-20k (DS-20k) and DarkSide-Low Mass (DS-LM). The dominant radioactive isotopes produced in LAr include $^{3}H$, $^{37}Ar$, $^{39}Ar$, and $^{42}Ar$. Due to its long half-life and the difficulty separating it from $^{40}Ar$, $^{39}Ar$ is especially important for experiments looking for signals below 565 keV, while $^{42}Ar$ may pose a background to MeV-scale rare event searches. In experiments looking for a rare event like DS-20K and DS-LM, the presence of $^{39}Ar$ can cause a signal pile up or limiting backgrounds. Atmospheric argon (AAr) has a specific activity of 1 Bq/kg for $^{39}Ar$, and DS-50 measured the specific activity of $7.4*10^{-4}$ Bq/kg in underground argon (UAr). Additional reduction may be achievable through isotopic distillation with the Aria facility. At these levels, cosmogenic activation of radioactive isotopes may pose a significant contribution to the total activity, and achieving high radiopurity requires transportation and storage plans that account for the target$'$s activation in transit and storage. To this end, a software package is being developed for evaluating the activation of radioisotopes in UAr and AAr, based on a compiled selection of reaction cross section measurements and models, the PARMA and Gordon cosmic-ray flux models, and the user-specified transportation history and initial composition of the target argon. These calculations will be validated for $^{37}Ar$ activation in DS-50, comparing the software's predictions to the measured activity in DS-50 after the initial UAr fill. This code is designed to be flexible and easily extensible. The flux and reaction cross section models can easily be changed, and different cross section estimates and scaling factors can be used over different energy ranges, and capabilities for calculating the activation of other target materials may be added in the future. In the talk, I discuss the importance of cosmogenic activation calculations for low-background experiments, and how this code works.

Speaker: Teena Vallivilayil John (INFN)

LRTPosterDS20k.pdf

28 Radon déposition simulation and test

The radon deposition is a critical background for many underground experimment through it's daughter 210Pb. Depending on the energy region the final background could be influenced by 210Pb,210Bi or 210Po. The energy emitted by the contaminated pieces is influence by the depth of implantation. In this work, I present a simulation of penetration depth. This depth is simulated by Geant 4 but is also dependant on surface state of the material. I am also planning to present implantation measurement with radonisation chamber and present a comparison with simulated depth of implantation.

Speaker: guillaume warot

29 Mitigation of Cosmogenically Induced Background from ${}^{42}$Ar/${}^{42}$K using Encapsulation with Ultra-Pure Plastic for the LEGEND Experiment

Neutrinoless double beta (0$\nu\beta\beta$) decay is a most compelling approach to determine the Majorana nature of neutrino and measure absolute value of neutrino mass. The LEGEND collaboration is aiming to look for a rare nuclear decay, ${}^{76}$Ge $\rightarrow$ ${}^{76}$Se + e$^-$ + e$^-$. Cosmologically induced isotope ${}^{42}$Ar and its decay progeny ${}^{42}$K in a liquid argon could create irreducible background for the 0$\nu\beta\beta$ signal. We are studying the methodologies to mitigate the ${}^{42}$K background. In order to do this, encapsulation to germanium detectors with 3D printing technologies using low background material are currently under investigation. Simulation results of Poly Ethylene Naphthalate (PEN) encapsulation to germanium detectors and plans to study other perspective materials are presented.

Speaker: Ibrahim Mirza (University of Tennessee)

Poster_42Ar_LEGEND.pdf

30 The Study of 13C(α,n)16O reactions in the MAJORANA DEMONSTRATOR Calibration Data

Neutron-induced backgrounds are a key concern in low radioactivity experiments searching for rare events. One common source of neutrons is (α,n) reactions induced by α-particles from the radioactive isotopes present in detector materials. Since carbon-rich materials, such as plastic and epoxy, are often widely used in low-background experiments, 13C(α, n)16O could be a major source of neutrons. Precision cross-section measurements covering all relevant α-energies are sparse, so statistical model approaches such as TALYS are often used to estimate the cross-sections of (α,n) reactions. Therefore, understanding the validity and uncertainty in the TALYS-model approach is important. Using the MAJORANA DEMONSTRATOR, we analyzed 6129-keV isomeric photons emitted following 13C(α, n)16O reactions in its calibration data, which was taken on a weekly basis using line sources made of 228Th isotope encapsulated in carbon-rich materials. A useful comparison was made between the data and the prediction of 13C(α, n)16O reactions by TALYS-based software. In this talk, we will present this analysis and findings that is relevant in estimating the radiogenic neutron background for future low-background experiments.

Speaker: Mr Tupendra Oli (University of South Dakota)

LRT_2022_Poster_Tupendra.pdf

31 Cryogenic light readout of NaI(Tl) crystals for dark matter detection

The most discussed topic in direct search for dark matter is arguably the verification of the DAMA claim. In fact, the observed annual modulation of the signal rate in an array of NaI(Tl) detectors can be interpreted as the awaited signature of dark matter interaction. Several experimental groups are currently engaged in the attempt to verify such a game-changing claim in a model-independent way, i.e. with the same target material. However, all present-day designs are based on a light readout via Photomultiplier Tubes (PMT), whose high noise makes it challenging to achieve a low background in the 1-6keV energy region of the signal. Even harder it would be to break below 1 keV energy threshold, where a large signal fraction potentially awaits to be uncovered. ASTAROTH is an R&D project to overcome these limitations by using Silicon Photomultipliers (SiPM) matrices to collect scintillation light. The all-active design based on cubic crystals is operating in the 87-150K temperature range where SiPM noise can be even a hundred times lower with respect to PMTs. The cryostat was developed following an innovative design and is based on a copper chamber immersed in a liquid argon bath that can be instrumented as a veto detector. We have characterized separately the crystal and the SiPM response at low temperature and we have proceeded to the first operation of a NaI(Tl) crystal read by SiPM in cryogeny.

Speaker: DAVIDE D'ANGELO (INFN)

poster_lrt.pdf

32 Latest development of the specialty ultra-low background detector manufacturing

Invented in the 1970s, High-Purity Germanium (HPGe) detection technology is still the reference for gamma-ray spectroscopy. Its excellent detection properties are unanimously recognized: in particular, its energy resolution performance is still unparalleled to this day. Despite its challenging operating conditions, HPGe detectors have become increasingly suitable for use in very diverse environments: controlled environments such as labs, in-situ, in industrial ones with challenging constraints (narrow spaces, vibrations, heat…) and even in extreme conditions (very radiative environments, in space…).

Mirion Technologies has developed detectors to cope with the requirements of low radioactivity measurement: the Specialty Ultra Low Background (S-ULB) detectors. For the construction of a S-ULB detector, each element that enters its composition must be selected carefully to reduce as much as possible the intrinsic radioactivity of the detector itself. The S-ULB detectors achieved a consistent intrinsic radioactivity of the order of a few hundred counts per day and per kg of Ge.

Specific needs for low radioactivity measurements can be addressed. For example, a double preamplifier installation on a BEGe with AC decoupling capacitor compatible with low radioactivity component. Furthermore, the detector orientation of BEGe can be changed and modified to have for example, two detectors facing each other. This configuration increases the solid angle coverage by a factor and thus provides an optimized efficiency for large sample measurement. An increase of the crystal diameter of BEGe up to 105 mm leads to a large surface perfectly suited for large samples measurement. The ratio of active volume over internal radioactivity gets even more favorable. For the measurement of small volume samples, the SAGe Well detectors with a well diameter of 21mm provide a close to 4PI solid angle coverage. All the detectors can have specific design, low radioactivity material, with energy resolution like standard HPGe: 600eV@122keV and 1.7keV@1332keV for a 1.2kg BEGe. For low radioactivity techniques, this led to better minimum detection activity or reduce of the measurement time. The advantages and the performance of the latest development of Mirion Technologies S-ULB detectors will be presented here.

Speaker: Mr Damian Ralet (Mirion Technologies (Canberra) SAS)

33 Indium-115 based crystals for β-decay spectral shape measurement

Neutrinoless double beta decay (0νββ) is a rare nuclear transition. If it is observed, it would answer open questions about neutrino masse and nature. To convert the 0νββ half-life into the neutrino Majorana mass a precise knowledge of the Nuclear Matrix Elements (NMEs) is required, but their current evaluation is strongly model-dependent. The measurement of highly suppressed β-decay spectral shape is a benchmark to test and stress nuclear models, shading light on the gA quenching and possibly identifying its origin. A quenched value of gA produces a spectral distortion in highly-suppressed single β-decay spectra. These decays have a higher transferred momentum, more similar to 0νββ, and offer a unique probe of the gA quenching as they are not masked by any lower-order β-decays. In the list of interesting isotopes to be measured, Indium-115 is one of the most suitable due to the relatively high Q-value (497.954 keV) and half-life (4.41x10$^{14}$ yr). In the framework of the ACCESS (Array of Cryogenic Calorimeter to Evaluate Spectral Shapes) project, we evaluated the performances of two $^{115}$In-based crystals operated as cryogenic calorimeters at the underground laboratory of Gran Sasso. In this talk, we present the results obtained from the test of indium oxide and indium iodine crystals to study the spectral shape of $^{115}$In.

Speaker: Giovanni Benato (INFN Laboratori Nazionali del Gran Sasso)

34 Radon burden and Xe purification performance of the LZ hot zirconium getter

Experiments employing Xe and Ar as particle detectors often make use of heated zirconium getters to remove electronegative impurities from the gaseous phase. For low background experiments, a key design consideration is to choose a purifier model which is large enough to achieve adequate electronegative removal, but no larger than necessary to avoid excess radon emanation from the getter pills. Good heat exchange is another important factor, because high rate gas flow may cool the getter pills below the design temperature, particularly in the case of Xe. To inform the design of future experiments, we present data on the purification performance and radon burden of the purifier used by the LZ dark matter experiment (SAES Megatorr model PS5-MGT50-R-535). Xe gas flow rates up to 600 standard liters per minute have been probed, and the temperature of the getter bed and its pre-heater have been recorded. We also present measurements of the achieved electron lifetime in the LZ TPC, the radon burden of similar purifiers, and HPGe gamma screening measurements of getter progenitor materials.

Speaker: Carter Hall (University of Maryland)

LRT2022-poster-final.pdf

35 Low Low Background kTon-Scale Liquid Argon Time Projection Chambers

It is possible to increase sensitivity to low energy physics in a third or fourth DUNE-like module with better radiopurity measures and suitable modifications to a detector similar to the DUNE Far Detector design. In particular, sensitivity to supernova and solar neutrinos can be enhanced with improved MeV-scale reach. With a 136Xe doping in the liquid argon, the detector can also be used for neutrinoless double beta decay searches . Furthermore, sensitivity to Weakly- Interacting Massive Particle (WIMP) Dark Matter (DM) becomes competitive with the planned world program in such a detector.

Speaker: Dr Sagar Sharma Poudel

36 Development of pulse shape discrimination method for identification and rejection of alpha events in high purity germanium detectors

HPGe detectors made of material enriched in Ge-76 were and are used by many experiments (Heidelberg-Moscow, IGEX, GERDA MAJORANA, LEGEND) for searches of neutrinoless double beta (0vbb) decay. Their main advantage is high detection efficiency (detector = source), high intrinsic radiopurity and excellent energy resolution. In order to achieve high discovery potential of the 0vbb decay, the above listed features must be supported by ultra-low background of an experiment.

One of the most problematic background sources come from alpha decays taking place on the p+ contact of the HPGe detector. They may be caused by decay of Po-210 (T_{1/2} = 138.4 days) deposited on surfaces during the exposure of the detectors to an atmosphere containing Rn-222. If Po-210 is supported by Pb-210 (T_{1/2} = 22.2 years) it may pose practically a constant background source over the entire lifetime of the experiment. Alpha particles passing the dead layer will lose part of their energies and may contribute to the counts in the region of interest.

In order to be able to efficiently reject events induced by alpha decays a dedicated pulse shape discrimination method has been developed. A BEGe-type (point contact semi-planar) HPGe detector was studied, to which artificial neural network (ANN), projective likelihood (PL) and A/E methods were applied. These methods were calibrated and trained on gammas coming from Th-228 and Co-56 sources (single-site and multi-site events used as signal and background samples, respectively) and applied to real alpha events. A high count sample of alphas was obtained by depositing Po-209 on a gold foil, which was then placed on a p+ contact of the detector installed in a vacuum cryostat. About 10^6 alpha events was acquired for the analysis.

The performed analysis showed that the ANN, while effective for single-site gamma events, cannot be used to reject alpha decays because of their single-site nature and short rise times. On the contrary, the PL reduced the alpha activity by more than three orders of magnitude (factor limited by the statistics) while preserving more than 80 % of the events form the double escape peaks (signal-like events from Th-228 and Co-56) and only about 20 % of multi-site events (background-like events). Thus, this method promises to be very effective.

In this talk I will discuss details of the measurements procedures (preparation of the source, data acquisition), performed analyses (training/calibration of the methods, application to the Th-228, Co-56 and alpha spectra, comparison of effectiveness) and plans for further activities.

Speaker: Dr Krzysztof Szczepaniec (Jagiellonian University)

37 Characterizing the Impact of Veto Threshold Settings on Detector Backgrounds

A study was performed to look at the impact of varying the lower-level threshold settings of an ultra-low-background counting system’s (ULBCS) cosmic veto and the impact on background rates as seen by ultra-low-background proportional counters (ULBPC). The first ULBCS shield was constructed in the shallow underground laboratory at the Pacific Northwest National Laboratory (PNNL) over a decade ago and has been in near constant use since. Over the ensuing years adjustments to the threshold settings for the plastic scintillator veto detectors have been necessary as drift has been observed in the overall veto rate due to effects like photomultiplier tube (PMT) aging, but a full characterization study had not been performed to determine the optimal settings since initial construction. Two ULBPC detectors loaded with geologic-argon-based P10 count gas were loaded into the ULBCS and spectral data was collected on separate data acquisition modules. Counting on separate modules allowed a unique veto threshold setting to be specified for each detector DAQ module. An initial baseline background dataset was collected with the existing historic settings before the veto threshold settings were adjusted and new data collection began. The threshold settings were varied by a factor of 10 in either direction from the existing threshold to span the region where the muon and gamma features overlap in the differential pulse height spectrum recorded for the veto detectors. The characterization results will be presented.

Speaker: Kimbrelle Thommasson (Pacific Northwest National Laboratory)

38 Suggestion of mobile ultra-low background HPGe system

Most underground laboratories (UL) were originally constructed for studies of fundamental physics, such as dark matter and neutrino-less double beta decay experiments. The fundamental physics experiments mentioned require ultra-sensitive detection at underground. Similarly, ultra-low background facility is invaluable for studies of radionuclides analysis from the perspective of reducing the background radiation from cosmic ray. Especially, gamma spectrometry system using HPGe detector is one of main radionuclides analysis equipment in underground laboratories. However, since the system is focused on measuring detector material for physics experiment and sensitive to contamination, there is a limit to applying it to general environmental samples such as seawater, sediment, etc. And underground environment is disadvantageous in accessibility when many samples need to be analyzed. Recently, there is an issue due to Fukushima contaminated water. Our team judge that ultra-low background HPGe system would be effective for seawater sample in terms of shortening radionuclides analysis time of pretreatment and measurement. So, we are designing a mobile system that can be moved to vehicle. A system to satisfy minimum detectable activity of under 10 mBq is considered as a target of Cs-137 radionuclide, and research on the optimization between shielding technique and the meter water equivalent. In this paper, there are conceptual design of mobile ultra-low background HPGe system.

Speaker: Chang-Jong Kim (Korea Atomic Energy Research Institute)

poster, CJKIM.pptx

39 Background Explorer

Background Explorer is a toolkit for modeling backgrounds in sensitive detectors from radioactive sources. Originally developed for the SuperCDMS dark matter search, it is now open-source and freely available at https://github.com/bloer/bgexplorer. The components that make up the detector and shielding system, associated material assays of radioactive contamination levels, and radiation transport simulation outputs are all collected in a MongoDB database. Background Explorer provides a web interface to easily enter and edit all of these quantities, and interactively drill-down into how different sources contribute to the overall background budget, generating tables, charts, and spectra on demand.

Speaker: Sagar Sharma Poudel (Pacific Northwest National Laboratory)

BackgroundExplorer_LRT2022.pdf

40 Using ultra-clean conditions of the MAJORANA DEMONSTRATOR to measure unobserved 180mTa decay

The nuclear isomer 180mTa has yet to have an observed decay as it has an expected half-life of over 1015 years—which is much longer than the current age of the Universe. The conditions necessary to detect such a rare event exist only in ultra-clean, radio-silent detectors, such as the MAJORANA DEMONSTRATOR. The uniqueness of this isomer arises from the nature of its stability: the isomeric state of 180mTa is more stable than its ground state; in recording the decay of 180mTa, more accurate nuclear models can be created. Furthermore, if recorded, constraints can be applied to certain dark matter candidates, as some are expected to couple to the nucleus of atoms. This coupling would cause a forced deexcitation from the isomer to the ground state. If this deexcitation were not to be observed, better constraints could be applied to current dark matter models.
In the current attempt to detect the 180mTa decay, 15 kg of high-purity Ta disks will be placed within the germanium array at the core of the MAJORANA DEMONSTRATOR. They will remain there for one year while data is collected; the decay of 180mTa can be identified by the energy of the gamma rays emitted. The Ta disks will be arranged within seven different strings, five of them containing 34 disks and the other two containing 12 disks. The former arrangement will be divided into four stacks of disks, each separated by a germanium detector, while the latter will be divided into three stacks of disks also each separated by a germanium detector. Ultra-pure electroformed copper plating will act as the support structure of these strings.

Speaker: Samuel Schleich

41 Emanation and Diffusion of Radon through Gaskets for SuperCDMS SNOLAB

The SuperCDMS SNOLAB experiment, currently under construction, will attempt to directly detect dark matter particles. Shielding surrounding the experiment’s detectors will
reduce interactions of particles from radioactivity and cosmic rays. A gas purge will remove radon from gaps in the shielding to reduce backgrounds further. Gaskets used to seal
this purge volume must allow sufficiently low radon diffusion through them while emanating little radon into the purge volume. Radon diffusion, solubility, and permeability were
inferred by measuring the time-dependent radon concentration in a volume separated by gaskets made of EPDM, Zip-A-Way, and Silicone. Although the silicone tested has better
radon properties, EPDM also is sufficient and is easier to use, and so EPDM will be used for the SuperCDMS radon barrier, with ZIP-A-Way used to reduce diffusion and patch leaks.

Speaker: Richard Schnee (South Dakota Mines)

PosterRnDiffusionCoSSURFLRT.pdf

42 Analysis of Backgrounds for a Radon-Emanation System

Expected backgrounds for electrostatic PIN-diode radon-emanation systems consist of three basic terms: a grow-in term, due to radon emanating from the detection chamber itself; a decaying term, due to radon that is transferred into the chamber along with radon from the sample; and a term constant in time due to environmental backgrounds such as cosmic rays. The first two backgrounds should produce energies corresponding only to the radon-daughter peaks, while the third is expected to produce a continuous energy spectrum. To determine what is the dominant background for the South Dakota Mines emanation system, many background runs were co-added. Results indicate that environmental backgrounds are negligible, but the time dependence of radon-daughter decays is surprisingly close to constant in time, implying that the the grow-in and decay terms have near-equal amplitudes.

Speaker: Seth Bendigo

SB-Poster.pdf

LRT 2022 - presentations: Purification Techniques for Solids / Radon Detector

Convener: Eric Hoppe (Pacific Northwest National Laboratory)

43 Ultra-low background NaI(Tl) crystals for dark matter direct search

The SABRE project aims to a model-independent search for dark matter through the annual modulation signature, with an unprecedented sensitivity to confirm or refute the DAMA/LIBRA claim. To achieve this goal, SABRE is working to produce NaI(Tl) crystals with a very low background in the (1-6) keV energy region, dominated by radioactive contaminants in the crystals. Direct counting of beta and gamma particles of crystal NaI-33 with the SABRE Proof-of-Principle detector, equipped with a liquid scintillator veto at the Gran Sasso National Laboratory (LNGS) has demonstrated an average background rate of 1.20 ± 0.05 counts/day/kg/keV, which is a breakthrough since the DAMA/LIBRA experiment.
Particularly, the amount of potassium contamination is 2.2 ± 1.5 ppb, lowest ever achieved for NaI(Tl) crystals. Data acquired for about one year with the NaI-33 detector into a purely passive shielding have shown that, if the crystal vetoable internal contaminations are as low as in the NaI-33, the active veto is no longer a crucial feature to achieve the required sensitivity. In fact, our background model indicates that the rate is dominated by 210Pb decays and that a large fraction of this contamination is located in the reflector wrapping the crystal. Beside the replacement of this material, ongoing developments of the crystal manufacture are aimed at the further reduction of the intrinsic background. The present results represent a benchmark for the development of next-generation NaI(Tl) detectors with a projected background rate lower than ∼0.3 counts/day/kg/keV. With this level of background an array of NaI(Tl) scintillating crystals with a total mass of just a fraction of the present generation experiments can achieve the ultimate verification of the DAMA result in three years.

Speaker: DAVIDE D'ANGELO (INFN)

slides_LRT_SABRE.pdf

44 Purification of sodium iodide powder for the COSINE-200 experiment

The COSINE experiment has performed an extensive R&D to develop ultra-low background NaI(Tl) crystals for the next phase COSINE-200 experiment. A ton of radio-pure NaI powder should be prepared for the 200 kg NaI(Tl) detectors. A large-scale recrystallization facility was built and had been operating to mass-produce pure NaI powder. The successful reduction of radioactive contamination in the purified NaI powder was confirmed by an Inductively Coupled Plasma Mass Spectrometer (ICP-MS) and HPGe detectors. Crystals that grew with the purified powder prove a principle of the low-background NaI(Tl) detector. This presentation will discuss NaI powder purification from an R&D to the mass production process.

Speaker: Keonah Shin (Center for Underground Physics, Institute for Basic Science (IBS))

Purification of NaI powder for COSINE-200_LRT.pdf

45 Purification of CaF$_{2}$ crystal for double beta decay experiment

We report on inorganic crystal purification for double beta decay and cosmic dark matter search;
focusing on the NaI(Tl) and CaF$_{2}$ crystals.
The NaI(Tl) crystal will be applied to search for cosmic dark matter, verifying the annual modulating signal reported by DAMA/LIBRA collaboration.
The CaF$_{2}$ crystal will be applied to search for the neutrino-less double beta decay of $^{48}$Ca.

We have established a method for purifying NaI (Tl) crystals and succeeded in purifying the concentrations of uranium-series, thorium-series, and potassium to below the target concentration.
We will discuss the reproducibility of our purification method and prospect.

We are working on the purification of CaF$_{2}$ crystal, which is made from water-insoluble raw materials. CaF$_{2}$ is a crystal used to search for the double beta decay of $^{48}$Ca.
The goal of the purity in this crystal is as low as 1 $\mu$Bq/kg or less.

We measured the impurities in the crucible and CaF$_{2}$ powder before we made a molten product of the CaF$_{2}$.
We will consider the correlation between the purity contained in the materials around the crystal growth and the purity of the molten product.
The material selection policy and prospects for large volume detector system will be discussed.

Speaker: Ken-Ichi Fushimi (Tokushima University)

Fushimi_LRT2022.pdf

46 Preparation of the precursors for AMoRE-II crystals synthesis

Advanced Mo-based Rare process Experiment (AMoRE) is a series of experiments for the neutrinoless double beta decay of 100Mo using molybdate-based crystals, such as $^{40}$Ca$^{100}$MoO$_4$, Li$_2$$^{100}$MoO$_4$, or Na$_2$$^{100}$Mo$_2$O$_7$. AMoRE phase-II aims to reach the internal background level below 5 $\times$ $10^{-6}$ ckky (count/kg/keV/year) in ROI using ~200 kg of bolometric crystals, which means levels for radioactive contaminants thorium, uranium, and radium are supposed to be below several $\mu$Bq/kg. For such a “zero-background” experiment, preparation of the initial materials used for crystal production is crucial. Molybdenum trioxide powder enriched with Mo-100 isotope (>99.6% enrichment, JSC ECP, Russia), $^{40}$CaCO$_3$ powder depleted in $^{48}$Ca (FSUE Electrochimpribor, Russia), lithium and sodium carbonates (99.999% purity grade, off-the-shelf products) are main precursors used for the AMoRE-II crystal synthesis. This work will describe the purification, mass-production, and recycling of those precursors to perform such a high-scale experiment.

Speaker: Olga Gileva (Center for Underground Physics at Institute of Basic Science, Daejeon, KOREA)

LRT2022_AMoRE_purification_GilevaOlga_final.pdf

47 Recent progresses of the radon detector with an electrostatic collection

In the field of particle physics, various experiments have been designed in order to search for rare physics processes beyond the standard model. Radioactive noble gas radon is one of the major background sources below the MeV region in rare event search experiments. To precisely monitor radon concentration in purified gases, a radon detector with an electrostatic collection method is widely used. To extend the application of the Rn detector, we have constructed the calibration set up in the Kamioka underground laboratory and evaluated the detector performance by filling the Rn detector with various gases, such as purified air, argon, xenon, andtetrafluoromethane. In this presentation, we overview the recent progresses of the Rn detector development and give a future prospect of this study.

Speaker: Yuuki Nakano (Kamioka observatory)

radon_detector_20220615_upload.pdf

Banquet: Meet at the Rushmore Hotel ballroom (cash bar)

Banquet: Dinner at the Rushmore Hotel

Thursday, June 16

7:40 AM Hotel transport - Coffee/Breakfast

LRT 2022 - presentations: Purification Techniques for Liquids & Gases, incl. Rn

Convener: Markus Horn (SDSTA - Science)

48 Background measurements for Jinping Neutrino 1-t prototype at CJPL

In 2017-2020, Jinping Neutrino 1-t prototype has detected numerous MeV radioactive background events, 343 high energy muon events and muon induced neutrons. By Bi-Po coincidence, the U238 contamination of liquid scintillator (LS) is measured as $(6.98 \pm 0.73) \times 10−13$ g/g, and Th232 upperlimit is $3.7 \times 10−13$ g/g (95% C.L., preliminary). On PMT glass, K40 contamination is $(5.73 \pm 0.79stat. \pm 1.49sys. ) \times 10−8$ g/g and Tl208 event rate is $(3.86 \pm 0.26stat. \pm 0.85sys. ) \times 10−3$ Bq/g, indicating $(2.64 \pm 0.18stat. \pm 0.58sys. ) \times 10−6 g/g$ Th232. The radioactivity of LS will be further suppressed after the distillation system is online. The muon flux is $(3.61 \pm 0.19stat. \pm 0.10sys.) \times 10−10 \mathrm{cm}^{−2}\mathrm{s}^{-1}$ with an average energy of 340 GeV, and its neutron yield is $(3.44 \pm 1.86stat. \pm 0.76syst.) \times 10−4μ−1g−1cm2$. Those results indicates that CJPL is an ideal place for low background experiments. We are making steady progresses on lowering radioactive isotopes of detector materials.

Speaker: Yiyang Wu (Tsinghua University)

LRT2022JinpingNeutrino.pdf

49 Improving nEXO Sensitivity with Radon Distillation

nEXO is a 5 tonne neutrino-less double beta (0vBB) experiment looking for this Standard Model forbidden decay in $^{136}Xe$. If this decay is observed it would mean that neutrinos are Majorana fermions, i.e. their own antiparticle, and that lepton number is not conserved. The nEXO experiment is designed to achieve a $1.35\times 10^{28}$ year half-life sensitivity (at 90% confidence level), about 10 events in 10 years of running. In nEXO, liquefied enriched xenon (LXe) fills a single drift Time projection Chamber with scintillation readout. The detector is built with ultra-low radioactivity materials, including an electroformed copper xenon vessel. The sensitivity of the experiment could be further increased by virtually eliminating radon dissolved in the LXe. A cryogenic distillation column that reduces the radon in xenon 100-fold would increase nEXO’s sensitivity to $>1.7\times10^{28}$ years. We will report on the progress of R&D on cryogenic distillation of LXe ongoing at the SLAC National Accelerator Laboratory.

Speaker: Brian Mong (SLAC)

220617 LRT Improving nEXO Sensitivity with Radon Distillation.pdf

50 Krypton Removal via Gas Chromatography for the LZ Experiment

Trace radioactive noble elements are a potential source of electron recoil backgrounds in liquid xenon-based detectors. Commercially available research-grade xenon contains krypton at a concentration of up to 10-7 g/g as a byproduct of its extraction from the atmosphere. About 1 part in 1012 of this residual krypton is krypton-85, a beta emitter with an endpoint energy of 687 keV and a half-life of 10.8 years. The science goals of the LZ dark matter experiment require that the ten tonnes of detector xenon contain a total krypton concentration of no more than 3×10-13 g/g. To achieve this, a gas charcoal chromatography system was built and operated at SLAC to remove krypton from the xenon prior to deployment in the detector. Using two charcoal columns in parallel to continuously process xenon, the system was automated to operate nearly 24 hours per day, and achieved a final purity of 1.1×10-13 g/g krypton in the full ten tonnes of xenon. In this talk, I will give an overview of the design and operation of the LZ krypton removal system at SLAC, and discuss some of the unique challenges encountered and lessons learned during the purification campaign.

Speaker: Mr Drew Ames (Stanford University)

LRT 2022 - Kr removal - 2022.06.16.pdf

51 Observation of Radon Mitigation in MicroBooNE by a Liquid Argon Filtration System

The MicroBooNE liquid argon time projection chamber has proven to be an excellent detector to study physics at the MeV-scale. It employs a large-scale liquid argon filtration system, using copper-based filters, to remove electronegative impurities from liquid argon to achieve and maintain a high level of purity. One prevalent background in this energy range is the decay of radon and its decay products. To study the system's efficacy in removing this radioactivity, a 500 kBq 222Rn source is placed in the cryogenic system upstream of the filter and MeV-scale reconstruction is leveraged to search for activity in the MicroBooNE TPC. The filtration system was able to remove more than 99.999% of the radon injected into the system. This is the first time that radon mitigation has been observed with a copper-based filter on a large scale and such filters may offer a viable radon mitigation option to support low-energy physics analysis in future large liquid argon time projection chambers, such as the Deep Underground Neutrino Experiment (DUNE).

Speaker: Joseph Zennamo (Fermilab)

RadonFiltration_LRT_June_2022.pdf

52 Material assay campaign of the DarkSide-20k experiment

The DarkSide-20k experiment will search for dark matter in the form of WIMPs and has the potential to set the best limits for the spin-independent interaction of heavy WIMPs with nucleons. The background requirement of this experiment is less than 0.1 events in 200 tonne years, which is the most stringent one ever set so far in the field of rare event searches and establishes rigorous requirements in terms of radiopurity of the detector materials.
A thorough assay campaign has been running for five years to assess the radiopurity of candidate components, paying particular attention to the U and Th decay chains. Different assay techniques have been adopted to be sensitive to the chain parents (ICPMS), the gamma emitters through the chain (HPGe), and the often ignored Po-210 content in the bulk of the materials. In such a way, it is possible to systematically investigate the secular equilibrium of the decay chain in all the materials. A specific mass spectrometry campaign has been added to the radioassay campaign to find out the chemical composition of the critical components of the detector, minimizing the uncertainty of the neutron yield produced through (a,n) reactions.
In this talk, we present the organization of the assay campaign and its results to date.

Speaker: Vicente Pesudo (CIEMAT / Lab. Sub. Canfranc)

LRT_MaterialAssayCampaignDarkSide-20k.pdf

10:00 AM Coffee / Refreshments

LRT 2022 - presentations: Assay and Screening Techniques

Convener: Andreas Piepke

53 Low background study for AMoRE through material screening facility at Y2L and Yemilab

The AMoRE experiment searches for the neutrinoless double-beta decay of $^{100}$Mo with cooled to milli-Kelvin temperature molybdate crystal scintillators. The maximum sensitivity for a given exposure is reached if a zero background in the region of interest is ensured. Therefore, various background reduction studies are ongoing to achieve the required background level for the experiment.
We conduct material screening using HPGe detectors to select low radioactive contamination material for the set-up and to characterize the radioactive components.
And background modeling using Monte-Carlo simulation is performed to estimate the background level from internal detector components.
In addition, external gamma-rays from the rock can be assessed by radioactivity measurement of rock samples from the Yang-Yang underground Laboratory where the experimental set-up is located.
The first phase of the AMoRE project, AMoRE-I, is taking data while the second phase, AMoRE-II, which used 100kg of the enriched isotope $^{100}$Mo, is in the preparation phase.
We will describe the HPGe detectors of CUP IBS (Center for Underground Physics, Institute for Basic Science), and present a background level study for AMoRE-II through the screening of most of the materials used in the experimental setup.

Speaker: Gowoon Kim (Center for Underground Physics, Institute for Basic Science (Korea))

LRT2022_GWKim.pdf

54 OSIRIS - The Online Scintillator Internal Radioactivity Investigation System of JUNO

The 20 kton liquid scintillator detector of the Jiangmen Neutrino Underground Observatory, currently under construction in Southern China, has a vast potential for new insights into various fields of (astro-)particle physics. Stringent limits on the liquid scintillator radiopurity are required for several physics goals of JUNO. For both $^{232}$Th and $^{238}$U, a radiopurity of $10^{-15}$ g/g is required for reactor antineutrino measurements, $10^{-16}$ g/g for solar neutrino measurements. An independent detector, the Online Scintillator Internal Radioactivity Investigation System (OSIRIS), will be used to ensure these limits are kept. This talk will present OSIRIS and its sensitivity to $^{232}$Th and $^{238}$U in detail.

OSIRIS allows an online radiopurity evaluation of the scintillator during the months-long filling of JUNO. The design of OSIRIS is optimized for tagging fast $^{214}$Bi-$^{214}$Po and $^{212}$Bi-$^{212}$Po coincidence decays in the decay chains of $^{238}$U and $^{232}$Th, respectively. The coincident decay signatures and their rates offer a potent background rejection as well as a direct translation into $^{238}$U-/$^{232}$Th-abundances in the scintillator. OSIRIS will also be able to measure the levels of $^{14}$C in the scintillator, down to a $^{14}$C/$^{12}$C ratio of $10^{-17}$ at 90\% C.L. Furthermore, the level of $^{210}$Po and a possible contamination by $^{85}$Kr can be determined. To achieve its goals, OSIRIS features a water-submerged 20 ton liquid scintillator target monitored by 76 intelligent PMTs (iPMTs). The novel design of the iPMTs allows a triggerless readout scheme with high signal quality. A single computer is sufficient to process the data stream into events for further analysis. The timing and charge calibration of the iPMTs will be performed with Laser- and LED-based systems. The energy and vertex reconstructions will utilise height-adjustable radioactive sources within the liquid scintillator.

Speaker: Moritz Cornelius Vollbrecht (Forschungszentrum Jülich GmbH, Nuclear Physics Institute IKP-2, Jülich, Germany / III. Physikalisches Institut B, RWTH Aachen University, Aachen, Germany)

LRT_OSIRIS_Cornelius_Vollbrecht.pdf

55 Use of QQQ-ICP-MS for Ultra Low Background Measurements

The advent of commercial atomic ICP-MS/MS has made it possible to measure low levels of actinides and other analytes without the need for extensive sample preprocessing. The instrument utilizes inline gas phase chemistry that either eliminates or reacts the analyte away from matrix derived interferences that otherwise need to be removed through separation techniques such as ion exchange column chemistry. This enables measurements of relevant samples such as electronics and their components (PCBs, solders, getters, etc.) that have matrices prone to create interferences in the region of the target analytes (e.g., Mo, Sn, W, Ir, Pt, Au, Pb on Th and U). It is difficult to make such low-level measurements with extensive chemistry as it is time consuming, often difficult and can be susceptible to contamination. We have investigated gas phase chemistry that would be suitable for such measurements – by investigating gases (O2, N2O, OCS, NH3) that react selectively with actinides and do no cause an unmanageable decrease in sensitivity due to scatter. We present some of the chemistries we have investigated that we believe will be useful for ultra-trace assay in a variety of matrices.

Speaker: Amanda French (PNNL)

LRT_Use of QQQ-ICP-MS for Ultra Low Background Measurements.pptx

56 Measurement of the argon purity by ICPMS and results of the analysis of the argon used for the MicroBooNE and ArDM experiments

Measuring the argon purity is critical for all Ar-based rare event research experiments. Mass spectrometry is typically used to measure U and Th contamination in samples of the materials used to build a low-background detector; however, this technique has the potential to provide other valuable information that is typically not exploited. At CIEMAT, we have shown that, by ICPMS, it is possible to identify and quantify contaminants in the argon. Preliminary tests were done with the gas extracted from the experiments MicroBooNE at FNAL and ArDM at LSC. In the former case, we identified some typical argon contaminants and compared the ICPMS results with those of commercially available argon gas. In ArDM, we identified and quantified the presence of mercury in the argon used in the experiment. This unexpected contamination had to be accounted for in the experiment's light propagation model.
This talk will present the idea behind this technique, the preliminary results, and some prospects for future experiments.

Speaker: Dr Roberto Santorelli (CIEMAT)

Santorelli_LRT2022.pdf

57 Radon Emanation Techniques and Measurements for LZ

Radon emanation is projected to account for ≈66% of the electron recoil (ER) background in the WIMP region of interest for the LUX ZEPLIN (LZ) experiment. The relatively long half-life of 222Rn leads to mixing within the target volume and an internal ER background with a beta-spectrum up to 1019 keV from its 214Pb progeny. To mitigate the amount of radon inside the detector volume, materials with inherently low radioactivity content were selected for LZ through an extensive screening campaign. The SD Mines radon emanation system is one of four emanation facilities utilized to screen materials during construction of LZ. SD Mines also employs a portable radon collection system for equipment that is too large or delicate to move to the radon emanation facilities. This portable system was used at SURF to assay the inner cryostat volume (ICV) in-situ at various stages of detector construction. In this presentation radon emanation, screening techniques, and noteworthy assays of LZ will be discussed.

Speaker: Nicholas Chott (SD Mines)

Chott_LRT2022.pptx

58 The Stawell Underground Physics Laboratory

The Stawell Underground Physics Laboratory (SUPL) is a newly built underground facility in regional Victoria, Australia. The laboratory is be located 1024 m underground (~2900 m water equivalent) within the Stawell Gold Mine and construction will be completed in May 2022. The laboratory will house rare event physics searches, including the upcoming SABRE dark matter experiment, as well as measurement facilities to support low background physics experiments and applications such as radiobiology and quantum computing. This talk will present the an overview of the SUPL design and current status, measurements of the laboratory background environment, and aspects of the SABRE construction.

Speaker: Lindsey Bignell (Australian National University)

SUPL_Bignell_LRT2022.pdf

12:10 PM Lunch - Grab'n Go

Excursions: SURF visit / Mt. Rushmore & Crazy Horse tourist excursion

Friday, June 17

7:40 AM Hotel transport - Coffee/Breakfast

LRT 2022 - presentations: Community Coordination and Databases / Cosmogenic Backgrounds & Material Activation

Convener: Vitaly Kudryavtsev (University of Sheffield)

59 Community Coordination and the Material Screening and Assay Program at SNOLAB

Astroparticle physics experiments searching for rare events, such as neutrinoless double beta decay and dark matter particle interactions, must be shielded from background radiation and must exhibit a radioactive background as low as reasonably achievable. The material selection for the next generation of low-background experiments is becoming crucial to inform the final design of the shielding scheme and to estimate the ultimate background rate in the energy region of interest of the experiments.
The SNOLAB material screening and assay program allows the direct measurement of the experimental background sources. In this talk, I will review the low background measurement capabilities at SNOLAB and will discuss plans and options to expand the facility to allow for the increased sensitivity required by the next generation of experiments along with community coordination within the Radiopurity.org database.

Speaker: Silvia Scorza

Screening_SNOLAB_Scorza_LRT2022.pdf

60 Low background counting calibration methods and considerations

Low background gamma spectrometry, specifically in the support of rare-event experiment material assays, presents a unique set of challenges and considerations from those found in traditional production counting facilities. A general overview of these challenges will be presented, along with some practical methods and approaches that vary in sophistication. Topics to be discussed include throughput, calibration samples/methods, analysis, and community round robins.

Speaker: Keenan Thomas

LRT2022_thomas_v2final.pdf

61 The Snowmass UF Supporting Capabilities topical group report

The 2021 particle physics community study, known as “Snowmass 2021,” has brought together particle physicists around the world to create a unified vision for the field over the next decade. One of the areas of focus is the Underground Facilities (UF) frontier, which addresses underground infrastructure and the scientific programs and goals of underground-based experiments. To this effect, the UF Supporting Capabilities topical group created two surveys for the community to identify potential gaps between the supporting capabilities of facilities and those needed by current and future experiments. Capabilities surveyed include underground cleanroom space size and specifications, radon-reduced space needs and availability, the assay needs and timeline for future experiments, and other space needs such as for crystal growth underground. In this talk, I will discuss the survey results and give a summary of the topical group report that has been written for the Snowmass process.

Speaker: Alvine Kamaha

SNOWMASS-UF04 Summary Report-LRT2022.pdf

62 Cosmogenic background and its consequences for rare event searches with germanium

When located on surface, rare event searches face various background sources. While most of them can be reduced by different shielding approaches, cosmogenic radiation is high enough in energy to still penetrate the experiments. Therefore, the only feasible solution remains to locate experiments deep underground. In my talk I will give an overview how germanium-based experiments handle this background. By showing studies from the MAJORANA DEMONSTRATOR data, I will illustrate which measures were taken to enable low-background searches for neutrino less double beta decay and other beyond standard model particles, even before the experiment data taking started. I will also show how the remaining in-situ cosmogenic background can be tagged and used to validate the results from simulations. By using delayed decay signatures, we were able to show how the muon-induced neutron flux contributes to remaining background deep underground. At the end I will give an overview on studies for the next generation effort LEGEND which aims reduce the remaining cosmogenic background component further.

Speaker: Ralph Massarczyk

Cosmogenic background and its consequences for rare event searches with germanium(2).pdf

10:00 AM Coffee / Refreshments

LRT 2022 - presentations: Cosmogenic Backgrounds & Material Activation / Experiment Backgrounds, Models & Simulations (1)

Convener: Pia Loaiza (IJCLab, CNRS, Université Paris Saclay)

63 Muon-induced background in a next-generation dark matter experiment based on liquid xenon

Muon-induced neutrons can lead to potentially irreducible backgrounds in rare event search experiments. We have investigated the implication of laboratory depth on the muon induced background in a future dark matter experiment capable of reaching the so-called neutrino floor. Our
simulation study focuses on a xenon-based detector with 70 tonnes of active mass, surrounded by additional veto systems plus a water shield. Two locations at the Boulby Underground Laboratory (UK) served as a case study: an experimental cavern in salt at a depth of 2850 m.w.e. (similar to the location of the existing laboratory), and a deeper laboratory located in polyhalite rock at a depth of 3575 m.w.e. Our results show that less than one event of cosmogenic background is likely to survive standard analysis cuts for 10 years of operation at either location. The largest background component that we identified comes from delayed neutron emission from 17N which is produced from 19F in the fluoropolymer components of the experiment. Our results confirm that a dark matter search with sensitivity to the neutrino floor is viable (from the point of view of cosmogenic backgrounds) in underground laboratories at these levels of rock overburden. I will present details of the performed simulations and of the obtained results.

Speaker: Viktor Pec

Cosmogenic_backgrounds_VPec_LRT2022.pdf

64 Methodology used in Borexino for the identification of cosmogenic long-time decay background

Borexino was a liquid scintillator detector situated underground in the Laboratori Nazionali del Gran Sasso in Italy, officially decommissioned in October 2021. Its successful and renowned physics program covers the study of solar neutrinos and spans also across geo-neutrinos and neutrino physics. Within its solar program, Borexino successfully measured neutrinos from the fusion processes in the pp chain and CNO cycle. Especially for the detection of pep and CNO neutrinos, an important background is formed by the cosmogenic radio-isotope $^{11}$C that is produced by muon spallation of $^{12}$C nuclei in the scintillator. Given the relatively long life time (30 mins) and high rate (30 cpd and 100 ton), specific signal identification is not possible. Borexino developed dedicated veto strategies in the data analysis phase to allow the detection of pep and CNO neutrinos.

The results presented so far by Borexino relied upon a Three-Fold Coincidence (TFC) technique that exploits the time and space correlation of muons, spallation neutrons, and radioactive $^{11}$C decays. However, this method has conservative assumptions during critical data-taking periods, such as during a board saturation case and in-between runs. That causes a loss of data exposure. Therefore, a new algorithm is devised to relax those TFC assumptions and deal with the critical periods by searching for space-time correlated bursts of $^{11}$C events produced in cascade by the spallation. In this work, we present the state of the art of the TFC, the new algorithm working, and highlight the performance of their combination to deal with the $^{11}$C background. Moreover, this method finds a general application in low radioactivity Borexino-like underground experiments when dealing with any background having a decay time too long to be identified by the triggers.

Speaker: alessio porcelli (Stefan Meyer Istitute)

2022.06.14-17 - Porcelli - 11C.pdf

65 The nEXO Background Control Program

nEXO is a planned ton-scale search for the neutrinoless double beta decay of 136Xe. nEXO intends to use 5000 kg of isotopically enriched liquid xenon as source and detector. In this talk I will discuss the approach nEXO has chosen to estimate, control and manage the experiment background, a subject important for all double beta decay experiments.

Speaker: Andreas Piepke

nEXO_RBC_v3.pptx

66 Modeling Backgrounds for the MAJORANA DEMONSTRATOR

The ${\rm M{\scriptsize AJORANA}~D{\scriptsize EMONSTRATOR}}$ is a neutrinoless double-beta decay ($0{\rm \nu\beta\beta}$) experiment containing ~30 kg of p-type point contact germanium detectors enriched to 88% in ${^{76}{\rm Ge}}$ and ~14 kg of natural germanium detectors. The detectors are housed in two electroformed copper (EFCu) cryostats and surrounded by a graded passive shield with active muon veto. An extensive radioassay campaign was performed prior to installation to insure the use of ultra-clean materials. The ${\rm D{\scriptsize EMONSTRATOR}}$ achieved one of the lowest background rates in the region of the $0{\rm \nu\beta\beta}$ Q-value, 11.9 $\pm$ 2.0 cts/(FWHM t y) from the low-background configuration of the initial 26 kg-yr exposure. Nevertheless this background rate is a factor of four higher than the projected background rate. This discrepancy arises from an excess of events from the ${^{232}{\rm Th}}$ decay chain. Background model fits aim to understand this deviation from assay-based projections, potentially determine the source(s) of observed backgrounds, and allow a precision measurement of the two-neutrino double-beta decay half-life. The fits agree with earlier simulation studies, which indicate the origin of the ${^{232}{\rm Th}}$ excess is not from a near-detector component and have informed design decisions for the next-generation LEGEND experiment. Recent findings have narrowed the suspected locations for the excess activity, motivating a final simulation and in-situ assay campaign to complete the background model.

*This material is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, the Particle Astrophysics and Nuclear Physics Programs of the National Science Foundation, and the Sanford Underground Research Facility.

Speaker: Christopher Haufe (University of North Carolina at Chapel Hill)

Haufe_LRT22.pdf

67 Background Mitigation Techniques in LEGEND

LEGEND (Large Enriched Germanium Experiment for Neutrinoless double beta Decay) uses High Purity Germanium detectors to search for lepton number violation in the neutrino sector with a multi-stage strategy. The HPGe detectors are isotopically enriched with Ge76 and immersed in high purity liquid argon, which serves simultaneously as a coolant, radiation shield and scintillation detector. 
LEGEND-200 is the first stage and is currently being installed. It is designed to achieve a factor of 3 decrease in background to 2e-4 cts/kg/keV/yr (@2039 keV) compared to the previous generation experiments GERDA and MJD. LEGEND-1000, the second stage, aims at decreasing the background further to 1e-5 cts/kg/keV/yr, projecting a quasi background-free dataset of 10 tonne x yr.
The technological improvements necessary to achieve the ambitious background goals include underground liquid argon, electroformed copper, ultra-clean cables and electronics, as well as powerful event discrimination techniques and careful active shield designs. This talk presents the overall projected background budgets in L200 and L1000 as well as the radio-purity techniques and analysis strategies required to achieve them.

This work is supported by the U.S. DOE, and the NSF, the LANL, ORNL and LBNL LDRD programs; 
the European ERC and Horizon programs; the German DFG, BMBF, and MPG; the Italian INFN; the Polish NCN and MNiSW; the Czech MEYS; the Slovak SRDA; the Swiss SNF; the UK STFC; the Russian RFBR; the Canadian NSERC and CFI; the LNGS and SURF facilities.

Speaker: Bjoern Lehnert (Berkeley Lab)

220617_LRT_LegendBg.pdf

12:10 PM Lunch

LRT 2022 - presentations: Experiment Backgrounds, Models & Simulations (2)

Convener: Douglas Leonard (IBS Center for Underground Physics)

68 Track-induced low energy backgrounds

In recent years, the search for dark matter with sub-GeV masses has been targeted by a variety of novel experiments that have reached the low-energy thresholds required for detection. Most of the experiments working in this unexplored kinematical regime have observed a large amount of excess events of unknown origin. In this talk, we show that Cherenkov radiation and luminescence originating from tracks passing through detector materials constitute a significant source for such events. We demonstrate that these processes can explain a large fraction of the events observed at the SENSEI, SuperCDMs HVeV and LAMPOST experiments. We also speculate on the possible implications for quantum qubit decoherence. Finally, we discuss concrete strategies that can be implemented at upcoming detectors to reduce these backgrounds.

Speaker: Daniel Egaña-Ugrinovic (Perimeter institute)

Backgrounds LRT.pdf

69 Stress Induced Background in Cryogenic Crystal Calorimeters

A number of low mass dark matter direct detection experiments have observed an excess rate of events, rising sharply below energies of around 100 eV. A similar source of background energy has been observed to shorten the coherence time of superconducting quantum bits by creating excess quasiparticles in the qubit circuit. The relaxation of stress in detector materials has been shown to cause low energy backgrounds in previous dark matter experiments, and has been proposed as a source of the current "low energy excess." By comparing detectors in high and low stress states, we have shown that stressing silicon detectors can cause excess event rates of over 80 Hz/gram below 20 eV, compared to a rate of under 0.5 Hz per gram in a low stress calorimeter. Measurements of the background rate as a function of time will be described, as well as implication for the design and operation of future cryogenic low threshold calorimeters.

Speaker: Roger Romani

Romani_Roger_Stress_Backgrounds_LRT_2.pdf

70 The background rejection capabilities of highly-pixelated solid-state detectors

Highly-pixelated solid-state detectors offer outstanding capabilities in the identification and rejection of backgrounds from natural radioactivity. I will present the background identification techniques developed for the DAMIC experiment, which employs silicon CCDs to search for dark matter. DAMIC has demonstrated the capability to disentangle and measure the activities of every $\beta$ emitter from the $^{32}$Si, $^{238}$U and $^{232}$Th chains in the silicon target. Similar techniques will be adopted by the Selena Neutrino Experiment, which will employ hybrid amorphous $^{82}$Se/CMOS imagers to perform spectroscopy of $\beta\beta$ decay and solar neutrinos. I will present the proposed experimental strategy for Selena to achieve zero-background in a 100 ton-year exposure.

Speaker: Prof. Alvaro Chavarria (University of Washington)

Chavarria_LRT_2022.pdf

71 Radiogenic background control strategy for the JUNO experiment

The Jiangmen Underground Neutrino Observatory (JUNO) is a massive multi-purpose underground liquid scintillator detector whose primary scientific goal is the determination of the neutrino mass ordering by measuring the spectrum of the oscillated antineutrinos originating from two nuclear power plants at about 53 km distance. The JUNO detector consists of a central liquid scintillator detector of 20 kton of mass, submerged in a water pool used as a water Cherenkov veto detector, and a top muon tracker. Thanks to its excellent expected performance JUNO has a rich scientific program that covers many crucial open issues of neutrino and astro-particle physics. Due to low neutrino cross section, the expected signal rate of reactor antineutrinos is only of about 60 events per day. It is therefore crucial to keep under control all possible sources of background. Radioactive nuclides mainly originate from the materials used in the construction of the experiment and they are able to produce background events that can mimic the signal of interest, thus reducing the sensitivity of the experiment. JUNO goal sensitivity to determine the neutrino mass ordering requires a rate of background events lower than 10 Hz in the whole fiducial volume.

In this presentation I’m going to show the big efforts of the JUNO collaboration in order to reduce the impact of the natural radioactivity on the detector performances. First, I’m going to discuss one of the most critical and complex topics, that is how the selection is performed on different types of materials and nuclides, up to $10^{-15}$ g/g of contamination level. Other critical aspects are the controls applied during the mass production of all the detector parts to ensure that the radiopurity requirements are met, and the work carried out to keep under control all the environmental radioactivity sources, such as radon emanation and dust. Finally, I’m going to show the dedicated Monte Carlo simulation program that was used to evaluate the contribution of each source to the final background rate to identify particularly critical components.

Speaker: Andrea Barresi (Unimib - INFN Milano Bicocca)

Andrea Barresi - LRT 2022.pdf

72 Neutron yield calculation with SOURCES4 and comparison with other codes and experimental data

Sensitivity of underground experiments searching for rare events due to dark matter or neutrino interactions is often limited by the background caused by neutrons from spontaneous fission and (alpha,n) reactions. A number of codes exist to calculate neutron yields and energy spectra due to these processes. Here we present the calculations of neutron production using the modified SOURCES4 code with recently updated cross-sections for (alpha,n) reactions and the comparison of the results with other codes and available experimental data. The cross-sections for (alpha,n) reactions in SOURCES4 have been taken from reliable experimental data where possible, complemented by the results of calculations with EMPIRE or TALYS codes where the data were scarce or unavailable.

Speaker: Prof. Vitaly Kudryavtsev (University of Sheffield)

LRT2022-alphan-sources4-VK.pdf

3:00 PM Coffee / Refreshments

LRT 2022 - presentations: Experiment Backgrounds, Models & Simulations (3)

Convener: Jaret Heise (Sanford Underground Research Facility)

73 External Radiological Backgrounds for the DUNE Experiment at Sanford Lab

The far detector of the Deep Underground Neutrino Experiment (DUNE) will be located 1500m underground at the Ross campus of the Sanford Underground Research Facility (SURF). The excavation of the two detector halls, that will house together four 17.5kt scale DUNE modules, has commenced. External radiological neutron and gamma-ray backgrounds from the rock, shotcrete and concrete have been evaluated based on a variety of radioactivity assays, as well as chemical composition assays, crucial for the production and propagation of neutron backgrounds. The results from both the extensive radioactivity assays and the extensive chemical composition assays have been utilized as informed input for Geant4 based simulations of the resulting external radiological neutron and gamma-ray backgrounds at the Ross underground campus for the DUNE experiment.

Speaker: Jürgen Reichenbacher

74 Low radioactivity argon for rare event searches

39Ar and 42Ar are irreducible backgrounds for several argon-based dark matter and neutrino experiments. The use of low-radioactivity underground argon (UAr) could be a solution to the problem. The DarkSide-50 experiment demonstrated that argon derived from underground sources can be highly depleted of 39Ar. Following this success, the Global Argon Dark Matter Collaboration (GADMC) is procuring hundreds of tons of UAr for the DarkSide-20k detector. However, there is a broader community need, making it is increasingly important to identify new sources of low-radioactivity argon. In addition, understanding the underground production mechanisms of argon radioisotopes and devising methods to measure them at ultra-low levels is necessary.
In this talk, I will discuss how the use of low-radioactivity argon could be crucial to expanding the physics goals and sensitivity of next-generation large-scale argon-based experiments. The underground production mechanisms of 39Ar and 42Ar will be discussed. 42Ar/42K decay backgrounds and an estimate of 42Ar production in the continental crust will be presented in some detail. Finally, the prospects of a kilo-ton scale UAr experiment will be discussed.

Speaker: Sagar Sharma Poudel

Sagar_PNNL_LRT_2022.pdf

75 $^{42}$Ar background in nEXO

The next-generation Enriched Xenon Observatory (nEXO) is a planned experiment utilizing 5 tonnes of isotopically-enriched liquid xenon (LXe) and a time projection chamber (TPC) to search for neutrinoless double beta decay of $^{136}$Xe. The large, monolithic design of the nEXO TPC provides excellent shielding from the dominant background source - $\gamma$ rays that originate from external materials. With an exceptionally clean central region of the TPC, we need to consider and quantify backgrounds that have previously been considered to be small relative to backgrounds from aforementioned $\gamma$ rays or not considered at all. A case in the latter category is $^{42}$Ar contamination in LXe. I will present the quantitative study of this $^{42}$Ar background for nEXO.

Speaker: Venkatesh Veeraraghavan (University of Alabama/Iowa State University)

42Ar_nEXO_LRT22.pdf

76 Latest results from the CUORE experiment: 0νββ limit and background model

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for 0νββ decay that has been able to reach the one-tonne mass scale. The detector, located at the LNGS in Italy, consists of an array of 988 TeO2 crystals arranged in a compact cylindrical structure of 19 towers. CUORE began its first physics data run in 2017 at a base temperature of about 10 mK and in April 2021 released its 3rd result of the search for 0νββ, corresponding to a tonne-year of TeO2 exposure. This is the largest amount of data ever acquired with a solid state detector and the most sensitive measurement of 0νββ decay in 130Te ever conducted, with a median exclusion sensitivity of 2.8×10^25 yr. We find no evidence of 0νββ decay and set a lower bound of 2.2 ×10^25 yr at a 90% credibility interval on the 130Te half-life for this process. In this talk, we present the current status of CUORE search for 0νββ with the updated statistics of one tonne-yr. We also show the latest results on the CUORE background model and the measurement of the 130Te 2νββ decay half-life, study performed using an exposure of 300.7 kg⋅yr.

Speaker: Dr Bradford Welliver (UC Berkeley)

LRT2022_bwelliver.pdf

77 The background model of the CUPID-Mo experiment

CUPID-Mo, located in the Laboratoire Souterrain de Modane, in France, was a demonstrator for CUPID, the next generation neutrinoless double beta decay experiment. CUPID-Mo consisted of 20 enriched Li$_{2}$$^{100}$MoO$_{4}$ bolometers and 20 Ge light detectors, and aimed to demonstrate that the technology of particle identification based on scintillating bolometers is mature for a ton-scale experiment.
We have developed GEANT4 Monte Carlo simulations with detailed geometry of the CUPID-Mo set-up, and applied the detector response in terms of resolution and light yield. The MC simulations, together with screening and other measurements, are used as input for the construction of a background model. In this work, we present the resulting background index in the $0\nu\beta\beta$ region of interest, and the extracted radiopurity of the bulk and surface contaminations of the Li$_{2}$$^{100}$MoO$_{4}$ crystals, which are found to be sufficient for the CUPID goals.

Speaker: Pia Loaiza (IJCLab, CNRS, Université Paris Saclay)

CUPID_Mo.pdf

78 LRT 2022 - Closeout

Speakers: Jaret Heise (Sanford Underground Research Facility), Richard Ford (SNOLAB), Richard Schnee (South Dakota Mines)

LRT2022 Closeout.pdf

LRT SC Update June 2022.pdf