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
Liquid Scintillator
ca. 50kt PXE/LAB
LENA
Inner Nylon Vessel
radius: 13m
Low-Energy
Neutrino
Astrophysics
Buffer Region
inactive, Dr = 2m
Steel Tank, 13500 PMs
r = 15m, h = 100m
 high demands on
the optical transparency
of the scintillator
Water Cherenkov Veto
1500 PMTs, Dr > 2m
Egg-Shaped Cavern
about 108 m3
Overburden: 4000 mwe
SCIENTIFIC GOALS
 Nucleondecay
 Supernova neutrinos
Diffuse SN neutrinos 
Geoneutrinos
 Solar neutrinos
Atmosphericneutrinos
 Neutrino propertiesby
reactors/accelerators
 Indirectdark matter search
Signal Energy and Timing
n
Energy Resolution
Light Yield (/MeV):
104
Photoactive Coverage:
30%
PMT Photoefficiency:
20%
+ Light Absorption/Scattering
Photoelectrons/MeV
<600
e
Light intensity in distance r:
I0
L
LENA Scintillator Characterization – Michael Wurm, TUM
initial intensity
attenuation length:
3
Signal Energy and Timing
Energy Resolution
Light Yield (/MeV):
104
Photoactive Coverage:
30%
PMT Photoefficiency:
20%
+ Light Absorption/Scattering
Photoelectrons/MeV
<600
Timing Resolution
Fluorescence constants:
fast component
ca. 3ns
slow component(s)
>20ns
Time of flight diff. O(100ns)
Light Scattering
Leading 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
Microscopic Processes
θ
Rayleigh Scattering
off bound electrons
in the scintillator
anisotropic emission:
orthogonal
parallel
to light
direction
Absorption/Reemission
off organic
molecules/impurities in
the liquid
isotropic re-emission:
fully polarized for
depends on
wavelength/production
LENA Scintillator Characterization – Michael
Wurm, TUM
Mie Scattering
off small particulates
(mm) in the liquid
anisotropic emission
increased forward
scattering amplitude,
depending on diameter
removable by filtering
5
Experimental Setup
measures
scattered
intensity
l=430±5nm
x10-5
monitors
beam intensity
measurement at several angles and for both polarizations determines
contributions of Rayleigh scattering, absorption-reemission etc.
LENA Scintillator Characterization – Michael Wurm, TUM
6
Exemplary Measurement Result
Sample:
Dodecane
Wavelength:
415nm
parallel
to beam
Q=Ns/Nb is the
(corrected) ratio
of PM intensities
orthogonal
to 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
Scattering Length Results
 no hints for Mie-scat.
 anisotropic scattering in
good agreement with
Rayleigh expectation
 correct wavelengthdependence found
 literature values for PC,
cyclohexane correctly
reproduced
Results for l=430nm
LS = 22±3 m
after purification
in Al2O3-column
Corrections and Uncertainties
 unevenness of sample glass surface:
 beam reflection on glass, alignment, refractive index:
 background subtraction of glass scattering:
 scattering solid angle (PM-S field of view):
 variation of PM-S efficiency with scattering angle:
 relative photoefficiency of the PMs:
 greyfilter transmission (wavelength-dependent):
4%
0.3%
diff.
4%
7%
7%
3.4%
(unc.)
(cor.)
(unc.)
(unc.)
(unc.)
(cor.)
(cor.)
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 experiments 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
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
Summary
Scattering length of all current LENA
scintillator candidates has been measured.
Impact on both light yield and
time resolution was tested.
LAB provides larger light yield, while
PXE (+C12) offers better time resolution.
LENA Scintillator Characterization – Michael Wurm, TUM
12