Radiological Background Model for DUNE MCCs Juergen Reichenbacher, Jason Stock, James Haiston DUNE Data Selection Workshop Penn State, 14-Aug-2018
Synopsis of Simulated Radiological Backgrounds impinging neutron flux 10 -5 cm -2 s -1 1.01 Bq/kg Ar-39 115 mBq/kg Kr-85 40 mBq/kg from Rn-222 92 uBq/kg Ar-42 impinging neutron flux (through all field cage sides and outer APA) 10 -5 cm -2 s -1 14-Aug-2018 J. Reichenbacher (SDSM&T) 2
Motivation of Radiological Model and Inputs from Screening => Requirements on Radiopurity driven by intrinsic Ar-39 level in LAr (1.01 Bq / kg) (would require Manhattan-Project style effort to mitigate for DUNE) - Radiological control is crucial for far detector (not so critical for ProtoDUNE) - Opportunity : use ProtoDUNE to validate that Ar-39 remains the by far dominant radiological background (and not some unexpected contamination) => Propose to continue with alpha- and gamma-screening of radiologically critical detector components for far detector AND ProtoDUNE to be used as inputs for radiological model - Full-blown radiological model is condensed into one LArSoft fcl producer file to be provided as input for SNB, DAQ, cosmogenics, atmospheric nus, pdk etc. - LArSoft simulations with full-blown radiological model (-> Jason Stock) validated requirements set on various radiological backgrounds 14-Aug-2018 J. Reichenbacher (SDSM&T) 3
DUNE Radiopurity&Purity Requirements for FD/protoDUNE Electron lifetime in liquid argon (subsequent requirements on O 2 , N 2 & H 2 0 levels): >3.0 ms -> Requirements on Radiopurity driven by intrinsic Ar-39 level (1 Bq / kg) Radon emanation requirement (e.g. G10 material for cathode): <75 mHz / m^2 (prelim.) Requirement for radioactive plate-out on surfaces (e.g. from radon daughters): <200 mBq / m^2 (prelim.) Requirement on radon content in liquid argon: <10 mBq / kg (factor 14 less than in 1 l air, factor 1000 more than XENON1t and 10000x more than LZ goal) -> commercial RAD7 counter will do to see 18 mBq / m^3 ? -> control filters with Ge/ICP-MS? 14-Aug-2018 J. Reichenbacher (SDSM&T) 4
Field-Cage and Cathode (3 mm thick G10 for now) G10 & FR4 g- screening results with low-background Ge-detector at Gran Sasso ( Claudio Montanari ) sample: Current Inc., C770 ESD (Electro-Static Dissipative material), G10/FR4 (glass/epoxy) weight: 89.0 g live time: 830876 s detector: GePaolo radionuclide concentrations: Th-232: Ra-228: (54 +- 8) mBq/kg <==> (13 +- 2) E-8 g/g Th-228 (49 +- 6) mBq/kg <==> (12 +- 2) E-8 g/g U-238: Ra-226 (47 +- 5) mBq/kg <==> (3.8 +- 0.4) E-9 g/g Dominant background as input: Pa-234m < 0.52 Bq/kg <==> < 4.2 E-8 g/g U-235 < 6.9 mBq/kg <==> < 1.2 E-8 g/g 4.9 Bq/kg measured for K-40 K-40: (4.9 +- 0.3) Bq/kg <==> (1.6 +- 0.1) E-4 g/g (Al profiles: only tens of mBq/kg Cs-137 < 3.7 mBq/kg upper limits with k=1.645, Co-60 & K-40 expected, neglected uncertainties are given with k=1 (approx. 68% CL); Ra-228 from Ac-228; but could be high in uranium) Th-228 from Pb-212 & Bi-212 & Tl-208; Ra-226 from Pb-214 & Bi-214; U-235 from U-235 & Ra-226/Pb-214/Bi-214 ======================================================================== G10 & FR4 a/b- screening with AlphaBACH at SDSMT (Juergen Reichenbacher): measured a -activity ACS grade isoprop, methanol No acid for cleaning on surface and acetone ok for cleaning of G10 & FR4! (native+precipitated+ (also DI-water) +plated-out radon daughters) is <<200 mBq / m 2 (requirement) 14-Aug-2018 J. Reichenbacher (SDSM&T) 5
Radon in LAr Rn-222 from dominant U-238 chain: Input for radiological model: 40 mBq/kg a -activity uniformly distributed in LAr to account for 4 subsequent a -decays of Rn-222 FD requirement on radon activity in liquid argon: <10 mBq / kg (factor 14 less than in 1 liter air, factor 1000 more than XENON1t goal and 10000x more than LZ goal) -> commercial RAD7 counter could be used? -> screen Ar filters with Ge/ICP-MS to control emanation? (requirement on radon activity of <10 mBq / kg guarantees that even in case of perfect secular equilibrium between early and late chain, induced rates are still one order of magnitude below Ar-39 induced rate) 14-Aug-2018 J. Reichenbacher (SDSM&T) 6
g -Screening of External Source Strength and of Critical DUNE Detector Parts - Received samples from 1 barrel of copper getter and mol sieve from ProtoDUNE ( from David Montanari & Stephen Pordes ) -> could introduce Rn-222 into LAr! - Samples are currently pre-screened with new Ge-detector at SDSMT and underground at SURF with low-background counter ( Kevin Lesko / LBNL ) - We have 50 barrels, i.e. 50 samples. Do we want to test them all? See 1 st results… - Pre- screener “Rabbit” at SDSMT is 2 blocks from ITF in Rapid City “Rabbit” BEGe g -detector at SDSMT allowing for large samples (12”x12”x12”) ( James Haiston ) Cu getter & mol sieve 14-Aug-2018 J. Reichenbacher (SDSM&T) 7
Co-60 in Steel Tubes of APA Frame Input for radiological model: 45.5 mBq/kg Co-60 g -activity in APA frame (MPIK Heidelberg’s highest measurement for a g -screened good commercial steel sample for GERDA, confirmed at Alabama & LBNL) 14-Aug-2018 J. Reichenbacher (SDSM&T) 8
Surface a -Activity on Photon Detectors Input for radiological model: 200 mBq / m 2 a -activity uniformly distributed across surfaces (~requirement of <200 mBq / m 2 for radioactive plate-out on surfaces, e.g. from radon daughters) a/b- screening with AlphaBACH at SDSMT (Juergen Reichenbacher): Eljen-280 WLS strips (directly from Eljen) meet quality assurance (QA) 14-Aug-2018 J. Reichenbacher (SDSM&T) 9
Surface a -Activity on Photon Detectors Quality control (QC) by a/b- screening with AlphaBACH at SDSMT (Juergen Reichenbacher): Eljen-280 WLS strips, coated TallBo plates & heat shrink contaminated during handling at IU, 1.5 Bq / m 2 although 1000x below NRC swipe sample (Am-241 sensitivity contamination) (but 1000x above AlphaBACH sensitivity) (Pu-239 calibration peak) In addition heat shrink shows excessive triboelectric effect, prolifically attracting radon daughters from air! 14-Aug-2018 J. Reichenbacher (SDSM&T) 10
Neutron Background for FD m uon flux at SURF’s 4850 level <10 -7 cm -2 s -1 neutron flux expected at SURF’s 4850 level ~10 -5 cm -2 s -1 Watt spectrum driven by U-238 content depends on isotopic composition of concrete, shotcrete and rock g -screen sand for concrete to be delivered to SURF? measure neutron yield with SDSMT He-3 tubes (started at Ross campus) add PE moderator sheets between concrete and insulating foam? adverse effect amplified by anti-resonance in neutron xs in Ar-40? (-> Bob Svoboda talk and PhD thesis Reichenbacher 2004) 14-Aug-2018 J. Reichenbacher (SDSM&T) 11
Neutron Background for FD measure neutron yield with SDSMT He-3 tubes (started at Ross campus) Prelim. : confirmed neutron flux of ~10 -5 cm -2 s -1 Still open question: Impact of correlated multiple fast neutrons from muon DIS/capture on SNB trigger 14-Aug-2018 J. Reichenbacher (SDSM&T) 12
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