Neutron background expectation Simon JM Peeters s.j.m.peeters@sussex.ac.uk JT DAQ Physics Performance WG 2019.11.21
In G4: ENDF Data Base, Neutron capture in LAr slightly different (worse) n + 40 Ar 41 Ar * : dominant n + 36 Ar 37 Ar * =0.978 Radiative neutron capture on Argon results in an excited atom of the next heaviest argon isotope. The excited argon isotopes de- excite with very specific total energy: 6.1 MeV for 41 Ar, 8.8 MeV for 37 Ar. This energy is carried away by at least one photon on the case of Hardell, R. and Beer, C., 1970. Thermal Neutron 37 Ar and at least two photons in the case of 41 Ar. Capture in Natural Argon. Physica Scripta , 1 (2-3), p.85. 2 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
Low energy events Neutron capture on 40 Ar: (Compton) e CC events See Pierre’s talk last time (and at/around CM): https://indico.fnal.gov/event/22378/contribution/0/material/slides/0.pdf 3 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
Simulation moving to full G4! Brief update from Aran at the end Aran, Tyler & Pierre – more details & motivation, see (amongst other talks): https://indico.fnal.gov/event/21861/session/6/contribution/20/material/slides/0.pdf 4 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
Neutron transport Effective neutron mean free path could be ~30 m! (ENDF: as currently in GEANT4) October 8-20 beam run Result expected by the end of the year 5 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
ACED arXiv:1902.00596 6 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
Background workshop was held at CERN in June https://indico.fnal.gov/event/20996/other-view?view=standard Report by review committee has been distributed but not published yet (?) 7 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
Overview Dominant (large mass): Subdominant (low mass/activity): 222 Rn in LAr: source of s: • Rock ( 238 U/ 232 Th) • 40 Ar( ,n) • Shotcrete ( 238 U/ 232 Th) • Insulation (glass fibre) • Support structure (1.5 ktonne) ( 238 U/ 232 Th) ( 238 U/ 232 Th/ 56 Fe( ,n)/ 54 Fe( ,n)) • Cryostat steel ( 238 U/ 232 Th, 56 Fe( ,n)/ 54 Fe( ,n)) Arxiv:1811.07912 TPC CuBe wires Be( ,n) • • APA steel / materials ( 238 U/ 232 Th) Also: cosmogenically-generated neutrons. Subdominant in rate, but possibly high- multiplicity events! 8 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
PS: Workshop on (α,n ) yield in low background experiments @ CIEMAT Today / tomorrow https://agenda.ciemat.es/event/1127/overview Vidyo: https://agenda.ciemat.es/event/1127/page/14-remote-connection Code: 232238 9 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
Neutrons from the rock DarkSide simulation (Paola Sala) (200 events / year / ton) * 10 * 10^3 tons / (3e7 sec / year) * • 18 [flux factor] * 10 [fiducialization factor] * • 3 [PUF foam moderation] * 3 [dead LAr shell extinction] = 108 neutrons / sec captured (J Reichenbacher @ CM https://indico.fnal.gov/event/21445/session/16/contribution/172/material/slides/0.pdf) in good agreement with: 104 Hz Aran Borkum, DUNE LArSoft (Geant4) 81 Hz Beacom et al (FLUKA) We expect a factor 3 shielding from insulation, so around: 30 n/s
Support structure • Mass of I-beam structure: 1.52 ktonne protoDUNE sample: 4.15 1.59 Bq/kg in 238 U (J Reichenbacher, SDSM&T, https://indico.fnal.gov/event/21625/contribution/0/material/slides/0.pdf) 238 U fission, 56 Fe( ,n) & 54 Fe( ,n): O(10) Hz (J Reichenbacher, SDSM&T, https://indico.fnal.gov/event/22323/contribution/0/material/slides/0.pptx) Stratification during manufacturing process ( 226 Ra out of equilibrium): sample steel coupons from different heights in smelt 11 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
Radon in LAr Vitaly (SOURCES4A): For 238 U+ 235 U chains in equlibrium the ( ,n) yield: 1.46*10 -10 n/g/s/ppb Radon and below: 1.37*10 -10 n/g/s/ppb For 232 Th chain in equilibrium: 8.71*10^(-11) n/g/s/ppb. Even for worst case, we expect: < 1 n/s. ((alpha,gamma) 13 gammas/day) (J Reichenbacher, SDSM&T, https://indico.fnal.gov/event/22323/contribution/0/material/slides/0.pptx) 12 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
CuBe wires (preliminary) Preliminary measurement at Boulby (David Waters): 3 Bq/kg 616.9 kg in one module. Vitaly (SOURCES4A) has provided expected ( ,n) yield: again, much below 1 n/s 13 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
Conclusions • Neutron rate is important and therefore we need to understand this in detail, measure the relevant activities in materials, and put in controls where we can. • Dominant sources are the rock, shotcrete and the I-beam steel. • Many other materials, we suspect subdominant, but assays are underway. • Full geometry simulations are underway to assess further the effect/use of any shielding. 14 2019.11.21 Simon JM Peeters | Neutrons in DUNE | DAQ PPWG
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