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Christian Buck, MPIK Heidelberg

Liquid scintillators. Christian Buck, MPIK Heidelberg. LowNu Reims, October 2009. Overview. Introduction Scintillator components Energy transfers Metal loaded scintillators Summary. Liquid scintillator past. Metal loaded: Reines Bugey Chooz Palo Verde. Unloaded: KamLand

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Christian Buck, MPIK Heidelberg

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  1. Liquid scintillators Christian Buck, MPIK Heidelberg LowNu Reims, October 2009

  2. Overview • Introduction • Scintillator components • Energy transfers • Metal loaded scintillators • Summary Reims, Neutrino Champagne 2009

  3. Liquid scintillator past • Metal loaded: • Reines • Bugey • Chooz • Palo Verde • Unloaded: • KamLand • Borexino Reims, Neutrino Champagne 2009

  4. Challenges: Stability and purity Palo Verde: KamLand Background: A.G.Piepke, S.W.Moser, V.M.Novikov; NIM A 342 (1999) 392-398 Chooz: Gd(NO3)3 τ ~ 240 days Chooz Coll.; Eur.Phys.C27, 331-374 (2003) Reims, Neutrino Champagne 2009

  5. Liquid scintillator properties • High energy resolution • Low energy detection threshold • high purity (Borexino) • fast signals (better understanding of timing properties) • moderate cost • Improved stability of metal loaded scintillators Reims, Neutrino Champagne 2009

  6. Liquid scintillator future • Double Chooz, Daya Bay, Reno • SNO+ • LENA,… Reims, Neutrino Champagne 2009

  7. Liquid scintillator components α, β, γ • Solvent • pseudocumene, toluene, anisole • „Safe scintillators“: PXE, LAB, DIN • Admixtures: alkanes, mineral oil • Primary fluor • PPO • BPO • Butyl-PBD,… • Secondary fluor • Bis-MSB • POPOP * PMT Reims, Neutrino Champagne 2009

  8. Comparison solvents: Light yield MPIK measurements M.Chen, INT Workshop 2005 Reims, Neutrino Champagne 2009

  9. Comparison solvents: Attenuation length MPIK measurements(UV/Vis, 10 cm cell) M.Wurm(TUM), ANT 2009 Reims, Neutrino Champagne 2009

  10. Purification methods • Column purification • Radioimpurities • Optics • N2 purging • Radon, 85Kr • Light yield (oxygen) • Water extraction • Radioimpurities (e.g. 40K) • Distillation • Radioimpurities • Optics Reims, Neutrino Champagne 2009

  11. Purification methods KamLand • Column purification • Radioimpurities • Optics • N2 purging • Radon, 85Kr • Light yield (oxygen) • Water extraction • Radioimpurities • Distillation • Radioimpurities • Optics CTF LAK Borexino Solar neutrino phase Reims, Neutrino Champagne 2009

  12. Borexino Background 40K < 3 ∙10-18 g/g 238U: 1.6 ± 0.1∙10-17 g/g 232Th: 6.8 ± 1.5∙10-18 g/g PRL 101, 091302 (2008) Reims, Neutrino Champagne 2009

  13. LAB • LAB is proposed in SNO+, Daya Bay, RENO • New high light yield, transparent solvent? • Used since decades • Average light yield • Average transparency • It is a high flash point, low toxicity solvent at moderate cost and reasonable optics, • …but: • Mixture • Biphenyls (absorption/emission!) • Timing properties LAB (6 g/l PPO) PXE (6 g/l PPO) Reims, Neutrino Champagne 2009

  14. Solvent mixtures Advantage: Parameters tuneable • optimize material compatibility • change timing properties • match density • adjust light yield 6 g/l PPO C.Aberle, diploma thesis, MPIK (2008) • Light production in alkanes • Radiation creates e-- - hole pairs • Recombination, fragmentation, radicals, reactions  excited molecules  energy transfer to fluors Light yield [% standard] PXE (mass fraction) M.Wurm, diploma thesis, TUM(2005) Reims, Neutrino Champagne 2009

  15. Comparison fluors BPO PPO • transparent • well established • high quantum yield • high(est) • light yield • emission around 400 nm • absorption properties • limited availibility pTP (Butyl-)PBD • high light yield • fast • overlap with bis-MSB • poor quantum yield • costs • low solubility • poor quantum yield Reims, Neutrino Champagne 2009

  16. Energy transfer (non-radiative) Reims, Neutrino Champagne 2009

  17. Critical concentration Critical distance R0: Donor * Acceptor 50 % 50 % Photon emission, decay Energy transfer Critical conc.: For PPO < 1g/l in PXE, PC,… For PPO ~ 2.1 g/l in dodecane Reims, Neutrino Champagne 2009

  18. Light yield model See poster by C.Aberle! C.Buck, F.X. Hartmann, D.Motta. S.Schönert, CPL, 435 (2007) 252 - 256 C.Aberle, diploma thesis, MPIK Heidelberg (2008) Reims, Neutrino Champagne 2009

  19. Timing properties Gamma Catcher candidates Events Target Time [ns] C.Aberle, Diploma thesis, MPIK Heidelberg (2008) D.Motta (CEA Saclay): pulse shape to tag events in different detector regions Reims, Neutrino Champagne 2009

  20. Metal loaded scintillators • Solar neutrinos (LENS, SIREN): • Metal: Ytterbium, Indium, Gadolinium • Challenge: High loadings • Reactor (Double Chooz, Daya Bay, RENO) • Metal: Gadolinium • Challenge: Stability • ββ-decay (SNO+) • Metal: Neodymium • Challenges: transparency; purity Reims, Neutrino Champagne 2009

  21. Indium Indium-loaded scintillators at LLBF > 1 year (2003/04) • MPIK:In(acac)3 (F.X.Hartmann et al.) • INR/LNGS: Carboxylic acid version > 50 g/l Indium D. Motta, C. Buck, F. Hartmann, T. Lasserre, S. Schönert, U.Schwan, NIM A 547 (2005) 368. N.A. Danilov, C.Cattadori, A..di Vacri et al., Radiochemistry 47 (2005) 487-493. Reims, Neutrino Champagne 2009

  22. Gadolinium (Carboxylates) Double Chooz mockup (TMHA, MPIK 2003): INR/LNGS: 2 x 1.2 t Gd-LS (0.1%) in frame of LVD arXiv:0803.1577v1 [physics.ins-det] 11 Mar 2008 • Now used in Daya Bay and RENO • Y.Ding et al., NIM A 584 (2008) 238-243. • M.Yeh et al., NIM A 578 (2007) 329-339. Reims, Neutrino Champagne 2009

  23. Gadolinium (β-diketones) • Purified by sublimation • stability/compatibility tests > 4 y • att. length (1 g/l) > 50 m in ROI • 100 kg produced Reims, Neutrino Champagne 2009

  24. Scintillator production for Double Chooz Scintillator production has started Poster by F.X.Hartmann on DC scintillator chemistry Reims, Neutrino Champagne 2009

  25. Neodymium MPIK (2003): Tests on BDK and CBX versions (F.X.Hartmann et al.) Light yield measurements at LNGS C.Cattadori et al., submitted to NIM A (2009) arXiv:0909.2152v1 [physics.ins-det] 11 Sep 2009 Reims, Neutrino Champagne 2009

  26. Summary • Liquid scintillators key technology for upcoming large scale neutrino detectors • Many solvent and fluor candidates • Choice depends on application and detector characteristics • Requirement for „safe“ scintillators (PXE, LAB,…) • Energy transfer models allow light yield predictions • Several applications for metal loaded scintillators  significant improvement in last years (stability etc.) Reims, Neutrino Champagne 2009

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