Introduction

WP1 members and mailing list current subscribers Mahanyapane Motlatsi Vincent (Stellenbosch University) BEAUPERE Nicolas (Subatech) THERS Dominique (Subatech) MORTEAU Eric (Subatech) Fabrice Piquemal (LP2i Bordeaux) Fairouz Malek WAROT Guillaume (LPSC-Modane) GUPTA Kaushik (Subatech) Luca SCOTTO LAVINA (LPNHE) SAUZET Nadine (LPSC) Paul Scovell (STFC Boulby Underground Laboratory) Rachid Mazini (Wits University) Ray Bunker (SNOLAB) Sara Diglio (Subatech) Silvia Scorza (LPSC Grenoble) BERTOU Xavier (IJCLab) XING Yajing (LPNHE)

Review of WP1 objectives, tasks, and responsible institutions (1.1, 1.2, 1.3) **Task 1.1 Innovative technology in radio-purity assay.** Institutions involved: UKRI, CNRS, INFN, LSC, SNOLAB, UWC, SURF This task aims to (i) reinforce and innovate the development of assay techniques to reach the sensitivities and throughput required for next generation low-background rare events experiments; (ii) establish better protocols for surface background mitigation; (iii) to foster the relationships between the assay facilities in Europe to offer a comprehensive, coordinated, and communal material characterisation for customers worldwide; to develop robust relationships between collaborators. There is great interest in low-background material radio-assay in the fields of particle physics, astroparticle physics, biophysics, environmental science and, increasingly, in the industry particularly focussing on single-event damage. This action can foster synergy between scientists working in this field and optimise workload sharing, increase sensitivity and ensure compatibility of results at different sites. **Task 1.2 New technology for radon-free environments.** Institutions involved: UKRI, CNRS, INFN, LSC, SNOLAB, UWC, SURF For rare event searches, Rn (222Rn) is a crucial source of background. In particular, exposing detector components to Rn will produce a plate out of 210Pb. This radioactive isotope has a half-life of 22 years and decays into 210Bi(β) → 210Po(α). The alpha in the decay of 210Po can mimic a nuclear recoil event and produce neutrons in the alpha-n reactions. Therefore, reducing lead plate out is a crucial background mitigation strategy. The goals of this task are complex research and innovation in the broad area of the Rn program. Activities will support cooperation between Proposers and cooperation with technological companies. The main results planned are new technologies and innovative devices. Rn mitigation is a critical issue in low background experiments during construction and running phases. This work will focus on Rn reduction and monitoring in air and studies on Rn transport and emanation in different pure gasses and material typically used in low background experiments. This task will also study how to innovate Rn abatement systems in collaboration with industrial partners to improve power efficiency and to provide the requested Rn-free air flow rate needed for innovative research programs for next-generation experiments. For this purpose, systematic studies of the pressure/temperature operation points and of innovative adsorption materials in high flow rate conditions will be performed. This task requires collaboration with Task1.1 for selection of materials. The task has per objective to co-ordinate the design efforts on an innovative Rn detector with a sensitivity of order mBq/m3; and to co-ordinate the design efforts and report on an innovative Rn abatement system. **Task 1.3 New protocols for production of radiopure materials to be used in detectors searching for rare processes.** Institutions involved: UKRI, CNRS, INFN, LSC, SNOLAB This task aims at improving the collaboration between scientists of underground facilities in order to identify improved protocols for the development of radiopure materials at the DULs. A large expertise has been acquired by scientists of low background experiments not only on low background materials but on lithography techniques: such expertise can be harnessed for the development of improved interposers for electronic circuits for future dark matter and neutrinoless double beta decay experiments. Interposers are the evolution of standard printed circuit boards in which the traces are deposited on crystal surfaces (fused silica, alumina, sapphire) that can be produced planar or, by means of advanced additive manufacturing, with custom 3D shapes. Fused silica wafers are synthesis products that can be delivered with high levels of (radio)purity, while there are studies about clean alumina. For the deposited electrical traces, high purity metal pellets can be obtained from electroforming. Laser trimming will allow encapsulation of resistors in the circuit without additional components. The task will initially focus on the preliminary research on the protocol to produce such interposer; after the lithography and additive manufacturing equipment will be available in one or more DULs it will be important to support the exchange of scientists between the different institutions in order to accelerate the finalization of the process and overall, the dissemination of the know-how. **Deliverables:** D1.1.1 Delivery of comprehensive cross-calibration for low background material assay of HPGe detectors across participating DULs. - M40 D1.1.2 Report on identification of suitably radio pure materials that may be used for future HPGe detector systems, along with further developments of the radiopurity.org database for sharing material and screening assay results (https://www.radiopurity.org/).- M30 D1.1.3 New protocols for sample treatment and automation prior to ICP-MS measurement to enhance the sensitivity. - M30 D1.2 Dissemination and publication of test results on Rn absorption, emanation, transport, and reduction in view of a next generation Rn abatement system. M30 D1.3.1 Definition of interposer technologies of interest, (M12) required equipment for the participating DULs and group responsibilities - M12 D1.3.2 Definition of the protocols for the accepted technologies - M24

Possibility of hosting remote round tables around Tasks 1.1, 1.2 and 1.3

Discussion of secondments and hosting plans