1. Analysis of the Optical Properties of Organic Liquid Scintillator in LENA DPG-Tagung in Heidelberg 9.3.2007 M. Wurm, T. Marrodán Undagoitia, F. v. Feilitzsch, M. Göger-Neff, L. Oberauer, W. Potzel, J. Winter Technische Universität München mwurm@ph.tum.de http://www.e15.physik.tu-muenchen.de/research/lena.html

2. 30m 100m DETECTOR PERFORMANCE photoelectron yield spacial resolution particle ID timing … SCINTILLATOR PROPERTIES light yield absorption length scattering length fluorescence times … optimisation of the scintillator  laboratory measurements are required 1/10

3. SCINTILLATOR INGREDIENTS SOLVENTSFLUORS PXE (C 16 H 18 ) density: 985g/l flamepoint: 160°C attenuation length: >10m ( after Al 2 O 3 purification) Dodecane (C 12 H 26 ) density: 749g/l flamepoint: 64°C attenuation length: >12m no purification, but lower light yield LAB (C 16-19 H 26-32 ) density: 863g/l flamepoint: 140°C attenuation length: >10m no purification, high light yield PPO (C 15 H 11 NO) primary fluor absorption band: 280-325nm emission band: 350-400nm high solubility pTP (C 18 H 14 ) primary fluor absorption band: 250-300nm emission band: 320-370nm low solubility, better match to bisMSB bisMSB (C 24 H 22 ) secondary fluor absorption: 320-370nm emission band: 380-450nm at emission high solvent transparency 2/10

4. current laboratory work light yield attenuation length scattering length fluorescence time 3/10

5. fluorescence time coincidence measurement motivation - a scintillation signal is steep in rise; its decay is described by several exponential decay functions - this functions are due to different excitation states of the fluor molecules and the energy transfer of the solvent to the fluor(s) - signal decay times are important parameters for the detector‘s time resolution or the analysis of fast decays e.g. p → K +  → µ + 8/10

6. fluorescence time coincidence measurement near PMT measures large signal that is used for start time information far PMT measures arrival times of single photons  time difference carries information about signal decay time scintillator sample: scintillation signal due to Compton scattering, two windows let escape the light gamma source 54 Mn, 834keV 9/10

7. fluorescence time coincidence measurement PXE 2g/l PPO PXE 6g/l PPO results so far - measurements using PXE as solvent show shorter decay times with increasing fluor concentration - at least 3 (most likely 4) time components are needed to fit the light curve - pTP is faster than PPO - adding bisMSB as a secondary fluor slows the signal decay next steps - test the influence of different solvents on decay times (LAB, Dodecane) - test of more uncommon fluors with larger Stoke‘s shift 10/10

8. scattering length scattering measurements motivation - in a large detector like LENA, the amount of scintillation light that reaches the PMs on the outer surface is strongly depending on the scintillator (solvent) transparency - the transparency of the scintillator is described by its attenuation length - attenuation combines to effects: absorption & scattering - while absorbed light is lost to the signal, scattered or re-emitted light contributes to the photoelectron yield and increases the energy resolution of the detector 4/10

9. scattering length scattering measurements focussing the beam concept - measuring the dependence of light intensity on scattering angle and polarisation - determine contributions of Rayleigh, Mie and absorption&re-emission-processes LED ~430nm collimators limiting the solid angle sample rotatable PM measures scattered light reference PM measures photons per light bunch polarisation filter 5/10

10. PXE sample (Al 2 O 3 purified) 6/10

11. scattering length scattering measurements preliminary results PXE:- scattering dominates absorption - large unpolarised component - no significant angle-dependence: absorption-reemission-process? Dodecane: - scattering length of 20m - low unpolarised component next steps - narrow-bandpass-filters for LED - comparison to attenuation length measurements 7/10