Model for DUNE MCCs Juergen Reichenbacher, Jason Stock, James - - PowerPoint PPT Presentation
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
Juergen Reichenbacher, Jason Stock, James Haiston
DUNE Data Selection Workshop Penn State, 14-Aug-2018
14-Aug-2018
2
Synopsis of Simulated Radiological Backgrounds
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 impinging neutron flux 10-5 cm-2 s-1
14-Aug-2018
3
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)
(not so critical for ProtoDUNE)
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
to be provided as input for SNB, DAQ, cosmogenics, atmospheric nus, pdk etc.
validated requirements set on various radiological backgrounds
14-Aug-2018
4
DUNE Radiopurity&Purity Requirements for FD/protoDUNE
Electron lifetime in liquid argon (subsequent requirements on O2, N2 & H20 levels): >3.0 ms
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)
14-Aug-2018
5
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 Pa-234m < 0.52 Bq/kg <==> < 4.2 E-8 g/g U-235 < 6.9 mBq/kg <==> < 1.2 E-8 g/g K-40: (4.9 +- 0.3) Bq/kg <==> (1.6 +- 0.1) E-4 g/g Cs-137 < 3.7 mBq/kg upper limits with k=1.645, uncertainties are given with k=1 (approx. 68% CL); Ra-228 from Ac-228; 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 g-screening results with low-background Ge-detector at Gran Sasso (Claudio Montanari)
Field-Cage and Cathode (3 mm thick G10 for now)
Dominant background as input: 4.9 Bq/kg measured for K-40 (Al profiles: only tens of mBq/kg Co-60 & K-40 expected, neglected but could be high in uranium) G10 & FR4 a/b-screening with AlphaBACH at SDSMT (Juergen Reichenbacher): measured a-activity
(native+precipitated+ +plated-out radon daughters) is <<200 mBq / m2 (requirement) ACS grade isoprop, methanol and acetone ok for cleaning (also DI-water) No acid for cleaning
14-Aug-2018
6
Radon in LAr
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)
Rn-222 from dominant U-238 chain: (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
7
g-Screening of External Source Strength and of Critical DUNE Detector Parts
(from David Montanari & Stephen Pordes) -> could introduce Rn-222 into LAr!
underground at SURF with low-background counter (Kevin Lesko / LBNL)
Cu getter & mol sieve “Rabbit” BEGe g-detector at SDSMT allowing for large samples (12”x12”x12”) (James Haiston)
14-Aug-2018
8
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
9
Surface a-Activity on Photon Detectors
a/b-screening with AlphaBACH at SDSMT (Juergen Reichenbacher): Eljen-280 WLS strips (directly from Eljen) meet quality assurance (QA) (~requirement of <200 mBq / m2 for radioactive plate-out on surfaces, e.g. from radon daughters) Input for radiological model: 200 mBq / m2 a-activity uniformly distributed across surfaces
14-Aug-2018
10
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, although 1000x below NRC swipe sample sensitivity (but 1000x above AlphaBACH sensitivity) In addition heat shrink shows excessive triboelectric effect, prolifically attracting radon daughters from air! 1.5 Bq / m2
(Am-241 contamination) (Pu-239 calibration peak)
14-Aug-2018
11
Neutron Background for FD
muon 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 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)
Watt spectrum driven by U-238 content
14-Aug-2018
12
Neutron Background for FD
Prelim.: confirmed neutron flux of ~10-5 cm-2 s-1 measure neutron yield with SDSMT He-3 tubes (started at Ross campus) Still open question: Impact of correlated multiple fast neutrons from muon DIS/capture on SNB trigger