WP4.1 Radiopurity and Background Mitigation

Convened by

Roberto Santorelli (CIEMAT, Spain) and Jim Dobson (KCL, UK)

DRD2 Liquid Detector Community Workshop, 20th April 2023

R&D to enable next-generation rare-event searches

• Most survey responses related to DM or 0vBB (LXe, LAr, LS)

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• Radiopurity/background mitigation critical for scale-up

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• Next generation requires 10-fold reduction in BGs:

Bulk contaminants ( ~10 uBq/kg)

Radon emanation ( ~0.1 uBq/kg)

Surface activity ( ~10 uBq/m² )

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Roma3 Univ.

UCL

Univ. of Chicago

Univ of Padova

KIT

Univ. of Sheffield

INFN Cagliari

Univ. of Krakow

Univ. of Edinburgh

Univ. of Marseille

INFN Legnaro

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SNOLAB

Univ. of Coimbra

UCL

LBL

SDSMT

KCL

CIEMAT

Univ. of Zaragoza

INFN Genova

IIT Chicago

Univ. of Mainz

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Thanks to everyone who provided input!

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• 25 groups total (9 via survey/contacted us, 16 we reached out to)
• Breakdown:
• By technology: LXe (11), LAr (10), Cryogenic (2), LS (1)
• By country: Italy (6), UK (6), Spain (3), Germany (2), France (1), Poland (1), Portugal (1), Canada (1), USA (4)

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• Inputs used as basis for R&D topics and deliverables (see next slide)
• N.B. if you haven’t provided input there is still time - just drop us an email

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* Aimed for coverage across experiments/technology and location

Overview of technology topics (scope)

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1. Fixed contaminants in detector materials: Improvements to assay methods (HPGe, ICP-MS, NAA) and internal bkg mitigation
2. Dispersed sources: Techniques to characterise and mitigate the internal sources such as ²²²Rn, ⁸⁵Kr
3. Cleanliness and surface contamination: Control and monitoring of dust, ²¹⁰Pb/²¹⁰Po plate-out during construction, assembly
4. Novel veto design/materials: mitigation such as active shielding
5. Tools for background evaluation: alpha-n yields, cosmogenic activation, detector simulations

Overview of technology topics (scope)

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• Fixed contaminants in detector materials: Improvements to assay methods (HPGe, ICP-MS, NAA) and internal bkg mitigation
• Dispersed sources: Techniques to characterise and mitigate the internal sources such as ²²²Rn, ⁸⁵Kr
• Cleanliness and surface contamination: Control and monitoring of dust, ²¹⁰Pb/²¹⁰Po plate-out during construction, assembly
• Novel veto design/materials: mitigation such as active shielding
• Tools for background evaluation: alpha-n yields, cosmogenic activation, detector simulations

Measurements and mitigation techniques

Calculation and impact

Veto

• Fixed contaminants in detector materials: Bulk contamination

• Gammas, alpha and neutron production
• Assay methods (HPGe, ICP-MS, NAA, Po-extraction)
• Full radiogenic characterization (full U/Th chains, other elements)
• Novel materials: EFCu

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R&D topics:

• Improvements to the assay methods: sensitivity in ~uBq/kg for techniques
• Demonstration of novel materials: properties, scale-up potential

• Dispersed sources: Contamination into the target material

Note: initial & online purification of target (85-Kr, 39-Ar, etc) in WP3.1.

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• Internal sources from Rn emanation, mobility of Rn plate-out daughters, making their way into the target
• Techniques to characterise materials (room and cryogenic)
• Mitigation techniques - barriers to prevent emanation, electroplating

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R&D topics:

• Sensitivity requirements for Rn emanation at both room and cryogenic temperatures
• Development of barrier materials to prevent Rn emanation

• Cleanliness and surface contamination: Contamination not in the bulk

• Control and monitoring of dust during the construction
• Dust in the active volume (gammas, alphas from the full U-238 and Th-232 chains)
• Control and monitoring of Rn plate-out during construction and assembly (¹⁰Pb/²¹⁰Po)

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R&D topics:

• Cleaning: passivation, electropolishing
• New techniques to measure surface contamination at <<100 μBq/m²
• Techniques for monitoring dust deposition during construction (~10 ng/cm²)

• Novel veto design/materials: mitigation such as active shielding

• Control of the external radiation
• Mitigation of the internal/external radiogenic neutrons
• Doped radiopure neutron moderating materials

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R&D topics:

• Radiopurity selection, material development, purification strategy
• Doping techniques
• Demonstration of this technique and scale-up potential

• Tools for background evaluation: alpha-n yields, cosmogenic activation, detector simulations

• Calculation/simulation tools to evaluate the impact of the radiopurity measurement on an experiment
• α,n yield (chemical composition and α,n cross-section)
• Gammas from activation (surface exposure)

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R&D topics:

• Techniques for high-stats simulations of shielded detectors
• α,n cross-section data for key materials - requirements on yields uncert.
• Activation models and tools for exposure tracking

High level deliverables (& milestones)

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• WP 4.1: “Radiopurity and background” → Wide range of tasks (novel materials, techniques, mitigation strategies, calculations…)
• It is very difficult to ensure that all the inputs received can be included in just a few deliverables
• We are planning to organize a meeting with the people who sent contributions to this WP
• Milestones after the WP-meeting
• High/low level deliverables

Current thinking on high level deliverables

1. Radioassay techniques at required sensitivity for next generation of rare-event search experiments (HPGe, ICP-MS, NAA, Po-extraction, Rn)

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• Mitigation through the development of novel materials, their selection/treatment, and clean manufacture. (doping, monitor, cleaning processes, barrier techniques)

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• Tools for the evaluation of backgrounds (alpha-n neutron yields, high stats simulations of shielded detector, cosmogenic activation)

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Broad scope to capture wide range of activities inherent in radiopurity and background mitigation

Next steps

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• Reorganization of all the inputs received, evaluation of the most recent ones

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• Finalization of this initial list of tasks and deliverables

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• WP meeting (in one/two weeks?). First proposal for the RP section for the proposal ready by that time

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• Section for the proposal with milestones and deliverables ready mid/end-May

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BACKUPS

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Resources available and needed

• List of institutions (with no info)
• FTEs (keep these as totals, do not give specific details per institutions) (see next slide for example table from Ines)
• Equipment/consumables
• Infrastructure (small vs large) (this may deserve its own slide of infrastructure for testing or demonstration is needed for more advanced R&D)

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Resources available and needed

Example table for FTEs (from Ines et al. draft presentation). E= Existing, R=Requested

Overlap and synergies with other groups

• Discuss the overlap with other WP
• Propose alternative deliverables based on potential mergers with other WP to see if people have comments on them
• Mention any ovelarp/synergies with other DRDs (this will be addressed later, but we need to start flagging them).

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R&D to enable next-generation rare-event

• Majority of responses address specific R&D needs of next generation LAr/LXe rare-event searches
• Radiopurity and background mitigation critical for scale-up
• Need 10-fold reduction in BGs:
• Bulk contaminants ( ~10 uBq/kg HPGe)
• Radon emanation ( ~0.1 uBq/kg)
• Surface activity ( ~10 uBq/m² )

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What do you think about this one? I can get original so we can edit and make style consistent. Or we could show a couple of plots from latest LXe/LAr searches?

• Relate the activities to future scientific goals

Credit: Aaron Manalaysay (LBL)