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LENA Scintillator Characterization

LENA Scintillator Characterization. Transregio 27 SFB-Tage in Heidelberg 9/10. Juli 2009 Michael Wurm. Outline. Properties of Scintillation Signal Scattering Length Experiment Light Yield Time Resolution. LENA Scintillator Characterization – Michael Wurm, TUM 1.

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LENA Scintillator Characterization

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  1. LENAScintillator Characterization Transregio 27 SFB-Tage in Heidelberg 9/10. Juli 2009 Michael Wurm

  2. Outline Properties of Scintillation Signal Scattering Length Experiment Light Yield Time Resolution LENA Scintillator Characterization – Michael Wurm, TUM 1

  3. Liquid Scintillatorca. 50kt PXE/LAB Inner Nylon Vesselradius: 13mBuffer Regioninactive, Dr = 2mSteel Tank, 13500 PMsr = 15m, h = 100m high demands onthe optical transparencyof the scintillatorWater Cherenkov Veto1500 PMTs, Dr > 2mEgg-Shaped Cavernabout 108 m3 Overburden: 4000 mwe LENA Low-EnergyNeutrinoAstrophysicsSCIENTIFIC GOALS  Nucleondecay Supernova neutrinosDiffuse SN neutrinos  Geoneutrinos Solar neutrinosAtmosphericneutrinos Neutrino propertiesbyreactors/accelerators Indirectdark matter search

  4. Signal Energy and Timing n Energy Resolution Light Yield (/MeV): 104 Photoactive Coverage: 30% PMT Photoefficiency: 20% + Light Absorption/Scattering Photoelectrons/MeV <600 Light intensity in distance r:I0 initial intensityL attenuation length: e LENA Scintillator Characterization – Michael Wurm, TUM 3

  5. Signal Energy and Timing Energy Resolution Light Yield (/MeV): 104 Photoactive Coverage: 30% PMT Photoefficiency: 20% + Light Absorption/Scattering Photoelectrons/MeV <600 Timing ResolutionFluorescence constants: fast component ca. 3nsslow component(s) >20ns Time of flight diff. O(100ns)Light ScatteringLeading edge determines timing Trailing edge for particle ID Light scattering has impact on both light yield and pulse shape ... LENA Scintillator Characterization – Michael Wurm, TUM 4

  6. Microscopic Processes orthogonalparallelto lightdirection θ Rayleigh Scattering off bound electronsin the scintillator anisotropic emission:fully polarized for Absorption/Reemission off organic molecules/impurities in the liquid isotropic re-emission:depends on wavelength/production process Mie Scattering off small particulates (mm) in the liquid anisotropic emission increased forward scattering amplitude, depending on diameter removable by filtering LENA Scintillator Characterization – Michael Wurm, TUM 5

  7. Experimental Setup measuresscatteredintensity l=430±5nm x10-5 monitorsbeam intensity measurement at several angles and for both polarizations determines contributions of Rayleigh scattering, absorption-reemission etc. LENA Scintillator Characterization – Michael Wurm, TUM 6

  8. Exemplary Measurement Result Sample: DodecaneWavelength: 415nmQ=Ns/Nb is the(corrected) ratio of PM intensities parallelto beam orthogonalto beam • main contribution: Rayleigh scattering (large polarization difference) • no discernible increase in forward scattering: minor Mie-contribution • small orthogonal component at 90°: absorption/re-emission processes LENA Scintillator Characterization – Michael Wurm, TUM 7

  9. Scattering Length Results • no hints for Mie-scat. • anisotropic scattering in good agreement with Rayleigh expectation • correct wavelength- dependence found • literature values for PC, cyclohexane correctly reproduced Results for l=430nm LS = 22±3 m after purification in Al2O3-column

  10. Corrections and Uncertainties • unevenness of sample glass surface: 4% (unc.) • beam reflection on glass, alignment, refractive index: 0.3% (cor.) • background subtraction of glass scattering: diff. (unc.) • scattering solid angle (PM-S field of view): 4% (unc.) • variation of PM-S efficiency with scattering angle: 7% (unc.) • relative photoefficiency of the PMs: 7% (cor.) • greyfilter transmission (wavelength-dependent): 3.4% (cor.)

  11. MC Simulation of Light Yield • Input Parameters: • event in the center • 104 photons/MeV • LENA radius: 15m • optical coverage: 0.3 • photoefficiency: 0.2 • attenuation length(from previous experi-ments at MPIK, TUM and SNO+ R&D) • overall range: 200-350 photoelectrons/MeV (optimum: 600pe/MeV) corresponding energy resolution at 1MeV: 7.1% to 4.6% • yield could be increased by state-of-the-art photocathodes (e ->40%) LENA Scintillator Characterization – Michael Wurm, TUM 10

  12. Impact on Time Resolution • Rise time determines resolution.General trends: • fast fluorescence component has largest impact on both rise time ts and decay flank ts • no effect of refractive index • lower scattering length smears out signal: ts larger • increase in attenuation length decreases ts LENA Scintillator Characterization – Michael Wurm, TUM 11

  13. Summary Scattering length of all current LENA scintillator candidates has been measured. Impact on both light yield andtime resolution was tested. LAB provides larger light yield, whilePXE (+C12) offers better time resolution. LENA Scintillator Characterization – Michael Wurm, TUM 12

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