LENALENAScintillator CharacterizationScintillator Characterization

Transregio 27Transregio 27SFB-Tage in HeidelbergSFB-Tage in Heidelberg

9/10. Juli 20099/10. Juli 2009

Michael WurmMichael Wurm

OutlineOutline

Properties of Scintillation Signal

Scattering Length Experiment

Light Yield

Time Resolution

LENA Scintillator Characterization – Michael Wurm, TUM 2

LENALENALow-Energy

NeutrinoAstrophysics

SCIENTIFIC GOALSSCIENTIFIC GOALS Nucleondecay Supernova neutrinosDiffuse SN neutrinos Geoneutrinos Solar neutrinosAtmosphericneutrinos Neutrino propertiesbyreactors/accelerators Indirectdark matter search

Liquid Scintillatorca. 50kt PXE/LAB

Inner Nylon Vesselradius: 13m

Buffer Regioninactive, Dr = 2m

Steel Tank, 13500 PMsr = 15m, h = 100m high demands onthe optical transparencyof the scintillator

Water Cherenkov Veto1500 PMTs, Dr > 2m

Egg-Shaped Cavernabout 108 m3

Overburden: 4000 mwe

Signal Energy and TimingSignal Energy and Timing

Energy ResolutionLight Yield (/MeV): 104

Photoactive Coverage: 30%PMT Photoefficiency: 20%+ Light Absorption/ScatteringPhotoelectrons/MeV <600

e Light intensity in distance r:

I0 initial intensityL attenuation length:

LENA Scintillator Characterization – Michael Wurm, TUM 4

Signal Energy and TimingSignal Energy and Timing

Energy ResolutionLight Yield (/MeV): 104

Photoactive Coverage: 30%PMT Photoefficiency: 20%+ Light Absorption/ScatteringPhotoelectrons/MeV <600

Timing ResolutionFluorescence constants: fast component ca. 3nsslow component(s) >20nsTime of flight diff. O(100ns)Light ScatteringLeading edge determines timingTrailing edge for particle ID

Light scattering has impact on both light yield and pulse shape ...

LENA Scintillator Characterization – Michael Wurm, TUM 5

Microscopic ProcessesMicroscopic Processes

Mie Scatteringoff small particulates (m) in the liquidanisotropic emissionincreased forward scattering amplitude, depending on diameterremovable by filtering

θθ

Rayleigh Scatteringoff bound electronsin the scintillatoranisotropic emission:

fully polarized for

orthogonalparallelto lightdirection

Absorption/Reemissionoff organic molecules/impurities in the liquidisotropic re-emission:

depends on wavelength/production process

LENA Scintillator Characterization – Michael Wurm, TUM 6

Experimental SetupExperimental Setup

measurement at several angles and for both polarizations determines contributions of Rayleigh scattering, absorption-reemission etc.

=430±5nm x10-5 monitorsbeam intensity

measuresscatteredintensity

LENA Scintillator Characterization – Michael Wurm, TUM 7

Exemplary Measurement ResultExemplary Measurement Result

parallelto beam

orthogonalto beam

Sample:Dodecane

Wavelength:415nm

Q=Ns/Nb is the(corrected) ratio of PM intensities

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 8

Scattering Length ResultsScattering 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 =430nm

LS = 22±3 mLS = 22±3 m

after purification in Al2O3-column

Corrections and UncertaintiesCorrections 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.)

MC Simulation of Light YieldMC 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 (->40%)

LENA Scintillator Characterization – Michael Wurm, TUM 11

Impact on Time ResolutionImpact on Time ResolutionRise time determines resolution.

General trends: fast fluorescence component has largest impact on both rise time ts and decay flank s

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 12

SummarySummary

Scattering length of all current LENAscintillator candidates has been measured.

Impact on both light yield andtime resolution was tested.

LAB provides larger light yield, whilePXE (+C12) offers better time resolution.

Scattering length of all current LENAscintillator 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 13