1. Materials and Assay WG Status Ray Bunker for the Materials & Assay WG DarkSide General Meeting, Pula, Sardinia June 14, 2016 1

2. Ray Bunker2 Outline I. The Materials & Assay WG II. Reminder of WBS Charge III. Assay Results IV. Assay Organization

3. I. The Materials & Assay WG Ray Bunker3  Jagiellonian University (Kraków)  Princeton University  Politechnic Milano  Petersburg Nuclear Physics Institute  University of Massachusetts Amherst  Temple University  CIEMAT  INFN  Black Hills State University  Pacific Northwest National Laboratory Weekly WG Meetings chaired by Henning Back via ReadyTalk (9203029), Mondays @ 9:30 am PDT, 6:30 pm CEST

4. Ray Bunker4 II. The 1.3 Subsystem 1.3 Materials WBS 1.3.1 – Background budget and assay priorities 1.3.2 – Process and materials development 1.3.3 – Materials assay radiopurity The Materials L2 manager will lead the development of a strategy for selecting and employing materials that maximize the physics reach of the detector by controlling backgrounds from multiple sources. The L3 managers on this team will develop background budgets to identify materials purity and assay requirements, develop processes and materials to meet radiopurity requirements, and perform assay to identify useful materials and validate processes and sources during the construction and commissioning process. Each of these L3 responsibilities is described in more detail below.

5. Ray Bunker5 II. The 1.3 Subsystem 1.3 Materials WBS 1.3.1 – Background budget and assay priorities 1.3.2 – Process and materials development 1.3.3 – Materials assay radiopurity Working closely with the simulations portion of the Software WG, this L3 Manager will lead a team to develop a detailed model of the Darkside- 20k detector, veto, target, and external subsystems to establish a background model. This model will be used to determine radioactivity risks to the experiment, and to set priorities for the radiometric assay of detector materials. Minimal activity in this L3 since Jan meeting PNNL group looking into setting up DS-20k simulation (thanks Paolo!) High priority, but progress will remain slow until funding is in place

6. Working within the engineering requirements coming from other WGs, along with the bulk, emanation, and surface radiopurity targets from the background budget L3, this L3 manager will lead a group that works to meet these combined requirements through four focus areas: 1.3.2.1 – Materials selection 1.3.2.2 – Materials processes & chemical processes 1.3.2.3 – Cosmogenic activation 1.3.2.4 – New materials development Ray Bunker6 II. The 1.3 Subsystem 1.3 Materials WBS 1.3.1 – Background budget and assay priorities 1.3.2 – Process and materials development 1.3.3 – Materials assay radiopurity Some progress toward selection of high-priority materials (see assay results) Progress on surface cleaning methods for metals @ Kraków  See next talk by Grzegorz Zuzel

7. This L3 oversees all materials radiopurity assay for Darkside-20k. This L3 will organize the assay capabilities throughout the Collaboration and develop an assay schedule. The assay challenges are organized into five focus areas: 1.3.3.1 – Gamma assay 1.3.3.2 – Radiochemistry and mass spectrometry 1.3.3.3 – Radon emanation 1.3.3.4 – Large area surface assay 1.3.3.5 – QA/QC of all materials radiopurity assay Ray Bunker7 II. The 1.3 Subsystem 1.3 Materials WBS 1.3.1 – Background budget and assay priorities 1.3.2 – Process and materials development 1.3.3 – Materials assay radiopurity Primary focus of WG since Jan meeting Progress on assay and assay organization (this talk)  Also, new DS-dedicated HPGe @ Temple (last talk in session by Jeff Martoff)

8. Ray Bunker8 III. Assays High-priority materials: Titanium = cryostat Teflon = TPC reflector SiPMs = detector Sapphire = SiPM tile substrate Additional assays: Fused Silica = Top/bottom boundary of TPC active volume 10” PMT = possibility for outer water veto NOTE: Assays over last 6 months have truly utilized capability and facilities distributed across the DS collaboration

9. Ray Bunker9 Titanium Under consideration as material of construction for cryostat:  Primary background concern: (α,n)  Goal from proposal: <1 mBq/kg of total activity from intrinsic impurities  Two assay samples: Ti sponge and Ti plate  Sample point of contact: Alex Chepurnov Ti Sponge Ti Plate Ti Parts

10. Ray Bunker10 Titanium – Sponge ≈3 kg of material from Solikamsk Assays: gamma counting (HPGe) & radon emanation Gamma counting results: Instrument = GeMPI2 @ LNGS Assay contact = Marco Carlini Counted for 41.5 days! 232 Th = 0.23±0.07 mBq/kg (late chain) < 0.41 mBq/kg (early chain) 238 U = 0.34±0.06 mBq/kg (late chain) < ≈9 mBq/kg (early chain) Radon emanation results: Instrument = Kraków emanation system Assay contact = Grzegorz Zuzel 1 kg emanated twice in 12 L chamber ≈30% uncertainty in limit values 220 Rn < 0.10 mBq/kg ( 232 Th chain) 222 Rn < 0.15 mBq/kg ( 238 U chain) Consistent with <1 mBq/kg target

11. Ray Bunker11 Titanium – Plate ≈1 gram samples dissolved from plates for analysis Assays: ICP-MS ×2 ICP-MS @ LNGS: Results are preliminary Potential issues: no replicates, efficacy of U/Th spike, unknown detection limits Assay contact = Marco Carlini Total mass analyzed = 0.856 grams Estimated uncertainty ≈30% 232 Th = 0.5 mBq/kg 238 U = 2.1 mBq/kg 40 K = 93 mBq/kg ICP-MS @ PNNL: Assay contact = Isaac Arnquist Same method as used for LZ Masses analyzed = 0.8/1.3/1.2 grams Uncertainties range from 3–20% 232 Th = 0.074/0.043/0.045 mBq/kg 238 U = 1.53/1.58/1.48 mBq/kg Detection limits: 0.002/0.006 mBq/kg 238 U/ 232 Th

12. Ray Bunker12 Titanium – Context What is considered good for titanium? LUX results (all via HPGe gamma counting) :  from arXiv:1112.1376  Sample Ti6 = used for cryostat body 232 Th < 0.24 mBq/kg 238 U < 0.19 mBq/kg (late chain) = 6.2±1.2 mBq/kg (early chain)  Sample Ti7 = cryostat flanges and endcaps 232 Th < 0.2 mBq/kg 238 U < 0.25 mBq/kg More recent LZ results: 232 Th < 0.25 mBq/kg (late chain) < 0.28 mBq/kg (early chain) 238 U < 0.09 mBq/kg (late chain) < 1.6 mBq/kg (early chain) Alternative material: Stainless Steel Cryostat would be more massive But SS (α,n) cross section is smaller Activity requirement of SS ≈ Ti HPGe Assay of AISI304L SS:  Used for much of DS50 cryostat  9.7 kg sample in GeMPI2 @ LNGS 232 Th = 0.8±0.3 mBq/kg (late chain) < 1.1 mBq/kg (early chain) 238 U = 0.4±0.2 mBq/kg (late chain) < 50–100 mBq/kg (early chain)  XENON100 – PRD 83, 082001 (2011): 232 Th < 0.03 mBq/kg 238 U < 1.8 mBq/kg  XENON1T – JCAP 4, 027 (2016): 232 Th = 0.21±0.06 mBq/kg 238 U = 2.4±0.7 mBq/kg Compare to Alex’s Ti plate: 232 Th/ 238 U ≈ 0.05/1.5 mBq/kg (early chain)

13. Ray Bunker13 Teflon Under consideration as material for TPC reflector:  Background concerns: (α,n), 210 Po on surfaces, radon emanation  Radiopurity in proposal: μBq’s/kg of bulk 232 Th/ 238 U (from DS NAA, also EXO)  Two samples: bulk Teflon and Teflon sheet  Sample point of contact: Peter Meyers Bulk Assays: ICP-MS @ CIEMAT New facility! Potential issues: unknown analyte recovery efficiency Assay contact = Roberto Santorelli Total mass analyzed = 0.5 to 5 grams 232 Th = 2–8 μBq/kg, 238 U = 12–37 μBq/kg ICP-MS @ PNNL Assay contact = Isaac Arnquist  Would be good to confirm CIEMAT results, but without DS funding must wait for opportunity to batch with other polymer assays Surface Assay: XIA @ Kraków Assay contact = Grzegorz Zuzel 210 Po < 45 mBq/kg (bulk estimate)

14. Ray Bunker14 Silicon Photomultipliers Primary TPC detection element:  Background concerns: (α,n), 210 Po on surfaces, radon emanation  Radiopurity in proposal: < 0.06/0.18 mBq/kg 238 U/ 232 Th (DAMIC limits)  Initial SiPM assay samples from DS-NUV-HD wafer 1  Sample point of contact: Graham Giovanetti  Distributed to 4 facilities for ICP-MS (3 pieces each) PNNL, BHSU, CIEMAT, LNGS – important cross-calibration exercise Agreed to use common ultrasonic cleaning method  Also intend to send some to Kraków for XIA surface assay PNNL Assay Sample 50×50 mm 2 tile from proposal Fig.

15. Ray Bunker15 SiPM Assay Results ICP-MS @ LNGS: Assay contact = Marco Carlini Total mass analyzed = 232 Th = ? mBq/kg 238 U = ? mBq/kg ICP-MS @ CIEMAT: Assay contact = Roberto Santorelli Total mass analyzed = 232 Th = ? mBq/kg 238 U = ? mBq/kg ICP-MS @ BHSU: Assay contact = Brianna Mount Total mass analyzed = 232 Th = ? mBq/kg 238 U = ? mBq/kg ICP-MS @ PNNL: Assay contact = Isaac Arnquist Total mass analyzed = 232 Th = ? mBq/kg 238 U = ? mBq/kg Coming Soon!

16. Ray Bunker16 Sapphire Under consideration as substrate for SiPM tiles:  Background concerns: (α,n), radon emanation  Radiopurity in proposal: ≈100 μBq/kg 238 U, 232 Th (EXO)  Just beginning to explore potential vendors  Sample point of contact: Graham Giovanetti  Assay methods under consideration – both require some R & D: ICP-MS @ PNNL – potentially in collaboration with nEXO R&D Laser-ablation ICP-MS @ BHSU & PNNL (ppt-level expectation, ±10% accuracy)

17. Ray Bunker17 Additional Assays – Fused Silica Used for top/bottom boundary of TPC active volume:  Primary background concern: (α,n)  Assumption from proposal: 10 μBq/kg 232 Th, <50 μBq/kg 238 U (from DS NAA)  Three samples: multiple grams of DS50 scrap  Sample point of contact: Peter Meyers ICP-MS @ PNNL: Assay contact = Isaac Arnquist Masses analyzed = 2.0/1.4/2.2 grams Uncertainties range from 1–6% 232 Th = 15/2/22 μBq/kg 238 U = 3/5/8 μBq/kg Detection limits: ≈0.2 pg U/Th

18. 18 Additional Assays – Large PMT Under consideration for outer water veto:  Background concerns: total gamma activity  Acceptable level: ≈1 Bq/kg 232 Th/ 238 U/ 40 K  Assay sample: 10” Hamamatsu R7081-SEL PMT  Sample point of contact: Gemma Testera  100 such PMTs may be available from KM3 for use by DS-20k  Hamamatsu glass: typically ≈1 Bq/kg 238 U/ 232 Th 10” 15” Gamma counting results: Instrument = old PGT Ge @ Temple Assay contact = Jeff Martoff Glass mass: ≈1.4 kg Counted for 3 days twice: stem down & stem up Stem-down results (efficiency for socket) : 232 Th = 0.45±0.25 Bq/PMT 238 U = 1.2 ±0.32 Bq/PMT Stem-up results (efficiency for glass) : 232 Th = 0.26±0.20 Bq/PMT 238 U = 0.26±0.09 Bq/PMT

19. Ray Bunker19 IV. Assay Organization 1. Webpage framework 2. Assay requests 3. Organization of results

20. 20 1. Webpage Framework Webpage philosophy: Minimize the amount of information that needs updating on most of the pages, particularly public pages (reduces need for a Web Master) Webpage design plans Have a main page that describes the DS program focusing on DS-20k; e.g. darkside.lngs.infn.it Links to various unique aspects of DS Links to pages with list of publications and presentations ordered by DS program (10,50,20k) Have a password protected area Main landing page with various information for only collaborators Links to Working Group pages, Alfresco, DS10 & DS50 pages and work, FNAL DocDB Display of collaboration calendar (weekly meetings, collaboration meetings) Password protected Working Group pages will be Twiki (or analogous) [twiki.org] Need for a common platform across the WG’s to make the information sharing easier. Maintained by individual WG’s Easy repository for various forms of information Brief description of WG charge Links useful webpages Documents will be stored in Alfresco, and linked from WG page. courtesy Henning Back

21. 21 2. Assay Request Assay coordinator: Isaac Arnquist Current implementation: Google doc forms http://goo.gl/forms/OcuzVJuiDR Step 1: Requestor Information Step 2: Sample details Step 3: Assay requests Ultimate goals: Request either initializes Materials Database entry or associates with existing entry Partially populates entry Request form is uploaded as a document to Document Database and is associated with Materials Database entry

22. Ray Bunker22 2. Assay Request Request form is echoed back to requestor via email as a PDF (and to Isaac) PDF is stored on google drive (Document Database) and eventually linked from assay results summary spreadsheet (Materials Database) Red = current/temp solution Blue = ultimate solution

23. Ray Bunker23 3. Results Organization: assay reports Sample Preparation Three Suprasil Fused Silica samples were received from Peter Meyers of Princeton University on behalf of the Darkside Collaboration. The three samples were arbitrarily named "Suprasil_1, Suprasil_2, and Suprasil_3". No sample pretreatment or cleaning was conducted, as the samples were etched in 30% (v/v) HF before receiving from Peter Meyers. Subsamples were cleanly removed from the sample and placed in cleaned and validated Savillex vials. A known amount of 229 Th and 233 U tracer was added for quantitation using isotope dilution (ID) ICP-MS methods. The fused silica was digested in cleaned and validated Savillex vials using a combination of 8 M nitric acid and concentrated hydrofluoric acid with gentle heating on a hot plate. After full digestion, the acid was evaporated to near dryness and reconstituted with 1.5 mL of 8M nitric acid. After the third evaporation, the sample was brought up in ca. 3 mL of 2% (v/v) nitric acid and analyzed via ICP-MS. Results and Discussion Results are given in ppt (pg/g) for Th and U. The instrumental standard deviation on the determined value is given as "+/- sd". Absolute detection limits [3*stdev blank of process blanks (n=5)] were calculated to be ca. 0.2 pg for both Th and U. Relative detection limits can be calculated for each sample: mass analyzed for each sample/absolute detection limit. All samples were deteremined above detection limits. Moreover, tracer recoveries were good among samples, with an average recovery of 98% and 95% for 229 Th and 233 U, respectively. Process blanks also had good recoveries near 100% for both 229 Th and 233 U. A note: The samples were received in a sealable, gas-evacuated bag (I like these bags). The samples were wrapped in a Kim-wipe-like material. In the future, I recommend not using Kim-wipes, unless they are certified cleanroom-grade as they can deposit small debris/dust onto samples. ThU Samplemass analyzed (g)pg/g+/- sdpg/g+/- sd Suprasil_11.97773.800.040.2670.016 Suprasil_21.44750.4900.0270.3760.012 Suprasil_32.20955.500.020.6700.022 Absolute Detection Limits pg Thpg U 0.2030.238 ICP-MS of fused silica by Isaac Arnquist  Will explore standardization of reports with the four SiPM assays

24. Ray Bunker24 3. Results organization: summary Temporary solution: Google doc spreadsheet: @ https://goo.gl/QVsr71 Maintained by: Isaac Arnquist & Ray Bunker Hosted by dedicated gmail account: darkside.20k@gmail.com Link to Request FormLink to Assay Report

25. Ray Bunker25 3. Results organization: summary Temporary solution: Google doc spreadsheet: @ https://goo.gl/QVsr71 Maintained by: Isaac Arnquist & Ray Bunker Hosted by dedicated gmail account: darkside.20k@gmail.com

26. 26 3. Results Organization: database Database Requirements: web interface to populate database web interface to pull information e.g. all assays performed for a given material ability to access database from other applications e.g. MC group may want to pull directly from the database flexibility to add fields in the future courtesy Graham Giovanetti

27. 27 3. Results Organization: database courtesy Graham Giovanetti 3 (or 4) record types

28. 28 3. Results Organization: database courtesy Graham Giovanetti

29. Ray Bunker29 Summary DS-20k Materials WG actively working to identify radiopure materials: Ti vs. SS for cryostat  leaning toward Ti (late-chain U/Th for Ti plate?) DS50 Teflon probably OK, but more assays needed SiPM analysis has begun  useful cross-calibration of ICP-MS facilities Starting to plan sapphire assays DS50 fused silica bulk contamination very low ( 210 Po also?) KM3 10” PMT reasonably low in U/Th to be considered for use in water shield Assay Organization: Further development of temporary solutions  assay requests & reporting of assay results Next step toward ultimate database solution? Remainder of Session: 210 Po on Metal Surfaces – Grzegorz Zuzel DS HPGe Detector @ Temple – Jeff Martoff Requests: http://goo.gl/forms/OcuzVJuiDR Summary spreadsheet: https://goo.gl/QVsr71

30. Ray Bunker30 Backups

31. Ultra low background germanium gamma-spectrometer “NIKA” 31 Detector number №1 №2 №3 №4 Material Ge-76 Ge-natural Ge-76 Total mass, g 1006 896 1056 968 Effective mass, g 630 680 980 642 courtesy Alex Chepurnov

32. 32 Sample mass, g Sample size, sm Chemical content Structural content Shape 3170Tispongepackages Material : titanium sponge Instrument : low background Ge detector “NIKA”, 660 m.w.e. Total measurement time: 547 hours IsotopeLine energy, (keV) Registration efficiency (%) Window, (keV) Count rate in window, (without baseline) (h -1 ) ) Self background (without baseline) (h -1 ) Activity (without baseline) (Bq/kg) 40 K1460,80,10±3±32,5· 10 -2 2,1· 10 -2 ≤1,7· 10 -2 208 Tl2614,50,06±3±39,1· 10 -3 2,0· 10 -3 (1,1 ± 0,7)* 10 -3 214 Bi609,30,18±3±31,4· 10 -1 9,1· 10 -2 (5,4 ± 2,2)* 10 -3 228 Ac911,20,14±3≤1,3· 10 -2 ≤5,7· 10 -3 ≤3,4· 10 -3 238 U(4,3 ± 1,8)* 10 -10 г/г (0.43 +- 0.18 ppb) 232 Th(7,5 ± 4,7)* 10 -10 г/г (0.75 +- 0.47 ppb) REMEMBER THE GOAL: 238 U < 0,10 ppb ~ 1 mBq/kg 232 Th < 0,25 ppb ~ 1 mBq/kg courtesy Alex Chepurnov

33. 33 1-liquid metal, 2-mould, 3-EB axial gun, 4-vacuum vessel, 5-electron beam ISSP - Axial electron gun, 60kW. Ti-sponge was melted by e-beam in the massive water-cooled copper mould. Ti-ingot Rolled sample ppb Th< 0.02< 0.03 U< 0.06< 0.10 The rolled sample 180x80x6 mm 1. ~ 1/3 of the ingot was taken 2. First stage rolling to minus ~ 25% width 3. Vacuum annealing 1h 700C 4. Second rolling to minus ~25% up to 6 mm Ingot 250x150x~20 mm courtesy Alex Chepurnov

34. 34 №1 Ti ingot – e-beam melting in water-cooled Cu crystallizer №2 Rolling ɛ=50% №3 Rolling Т=700С, ɛ=30%, cold rolling ɛ=10% №4 Rolling Т=900С, ɛ=30%, cold rolling ɛ=25% №5 Rolling ɛ =25%, vacuum annealing 1h 700C, rolling ɛ =25% №6 Cold and hot rolling with direction changing T=300C, ɛ=80%, Vacuum annealing 1h 450C BelgorodSU did ingots processing with the following study of mechanical properties

35. 35 Mechanical and U/Th properties Материал HV (hardness) σ 0,2, Mpa (conventional yield limit) σ в, Mpa (tensile strength) Industrial materials AISI 304210510 VT1-00 / GRADE 1110-140250-380300-450 AISI 316180-250250-450450-800 VT1-0 / GRADE 4120-160300-420400-450 VT16 (Al, V)170-400600-10001000-1500 Ingots/sheet from pure Ti-sponge U, ppbTh, ppb Original ingot from pure Ti- sponge 140 std.dev 30 150220 <0.003< 0.05 Sample №2 160 std.dev 53 410565 0.830.67 Sample №3 165 std.dev 10 420590 <0.003< 0.05 Sample №4 155 std.dev 15 250390 0.160.14 Sample №5 160 std.dev 45 280400 <0.0030.017 Sample №6150 std.dev 8 415575 1.111.25 REMEMBER THE GOAL: U < 0,10 ppb ~ 1 mBq/kg Th < 0,25 ppb ~ 1 mBq/kg