High resolution scintillation detectors for DBD

1. High resolution scintillation detectors for DBD Jean-stephane Ricol CENBG – CNRS - France ILIAS July 1-5, 2007 Blaubeuren

2. Outline • SuperNemo R&D : very promising results using liquid scintillator : • Motivations for using LS • Measurements made in CENBG – Bordeaux • Measurements made in INR - Kiev • Prospects and improvements : • Large size detector • High QE PMTs • Optimization of surface for light collection

3. Motivation and goal

4. Solid / Liquid scintillator • Same light yield • Different attenuation length Liquid : Latt > 10-25 m Expect high resolution even for large size detector ~ 20cm x 20 cm x 20 cm Solid : Latt ~ 3 m h = 2 cm FWHM = 7-8% h = 10 cm FWHM = 9-10% My talk is focused on LS results

5. Measurements in Bordeaux Choice of LS : LAB • Linear AlkylBenzene • High light yield (50% ant.) • Good transparency (Latt > 10 m) • High flash point (130°C) • Very low toxicity (literature data) Few measurements with liquid Bicron BC 531 (light yield 59% ant., latt = 3.5 m) for comparison

6. LAB emission spectra Made and measured in Dubna Need absorption spectrum measurement

7. Teflon Delrin 10 cm LS Teflon 5 cm LS Medium-size container PMT = Photonis 3” XP5312b QE ~ 33% LS active height = 5 or 10 cm (from bottom to PMT photocathode) 7 cm PMT is in the LS = direct light transmission

8. Simulation Medium-size container • Entry face in Kapton : • Very good breaking strength • with 25 µm thickness 60 times lower than breaking point • Very good chemical strength LS doesn’t damage it • After 6 months Kapton foil didn’t sweat any LS leak • Kapton is yellow and transparent -> need reflector : Al deposit

9. Aluminium deposit on Kapton Kapton foil Reference quartz Al sample in a smelter heated by 30 A currant (Tevaporation = 800 °C) Evaporation projects Al in 4pi, it stops when quartz measures ~ 100 nm deposit We obtain a good mirror All is inside a vacuum vessel (10-6 atm)

10. The test bench CENBG test bench Black box : LAB container + PMT (3” XP5312b Photonis) Electron source Spectrometer 90Sr source, 370 MBq E/E ~ 1% Range 0.4 – 2 MeV XY table DAQ electronics

11. Results : light emission and propagation BC-531 : light yield 59% ant., Latt = 3.5 m (data sheet) Dubna LS = LAB : light yield ~50% ant., Latt > 10 m (SNO+ values) LAB LS is much better than BC531 => Attenuation is more important than light yield Must compare emission+attenuation (l) measurements

12. Results : light collection LAB LS • Delrin vs Teflon : same values within the errors • Diffusing medium is better than reflecting medium on sides for this geometry (7 cm diameter, 5 cm high)

13. FWHM @ 1 MeV (%) Beam position (cm) Results : position effect No effect on resolution, light is emitted and collected independently of the interaction position

14. Results : size effect No effect as expected from large Latt • Comparison with plastic scintillators (same PMT as LS) • PS1 = 7.5 cm x 2 cm : 8.0% • PS2 = 7.5 cm x 10 cm : 9.8% Strong attenuation with solid  liquid is a much better candidate for large size detector

15. Prospects in Bordeaux • First of all we must prove the same promising results can be reached with large size container + 8” PMT • New container in construction, we will first test Kapton resistance (simulation of mechanical strengths claim it should be ok) • O2 purge by N2 bubbling should increase the detected number of photons by 10-20%

16. Measurements in Kiev Similar container 84×92 mm Different LS : Toluene + pTP 5 g/l + POPOP 0.1 g/l PETF film 0.5 mg/cm3 Add AlMyl teflon Pipe for O2 purging (pure argon) Similar QE PMT (Photonis 3” XP2412 QE ~ 33%) from A. Danevich et al

17. 207Bi Results FWHM = 7.4% @ 976 keV from A. Danevich et al • Resolution better than with LAB (7.4 vs 8.2 %) : • LS light yield or Latt higher ? need spectra measurement • O2 purge ? 15% more light collection : 8.2  7.6 %

18. Large container Mylar film 1.7 mg/cm2 23 cm Teflon container:volume 6.3 dm3 window area 3.5 dm2 5 ” PMT EMI 9390 Unfortunately the PMT is not of so good quality QE≈24% A.A.Adadurov et al.

19. 207Bi BG-subtractedspectrum Teflon tape 5.6 mg/cm2 +Aluminized Mylar 0.6 mg/cm2 207Bi Pileup of signals FWHM = 11 % (for 33% QE : FWHM  9.6%) Results for large container Resolution is not good (8% expected) Bad PMT ? High counting rate (18 kHz) ? A.A.Adadurov et al

20. Uniformity of light collection ●100(1)% ●100(1)% ●100(1)% ●100(1)% ●100(1)% Uniformity tested by moving the 207Bi source by 2cm step No difference was observed within 1% accuracy A.A.Adadurov et al

21. Prospects in Kiev • PMT with QE≈30% • Measurements in a shield to suppress BG counting rate • Lower activity 207Bi source

22. Light collection simulation Very promising results in both labs but still need to be improved : light simulation can help us to optimize photon collection and improve the resolution Geant4 : detector + particle interaction + light simulation Need detailed spectra : preliminary results simulated with PS data Simulation of PS block F20cmx20cm

23. Plot from E. Chauveau Refl. Diff. Refl % Refl. Refl. Diff. Diff. Light collection simulation Effect of light collection on side : reflection vs diffusion There is an optimization of the surface !! We can win 0.3-0.5% on the resolution Must try several layers and check it experimentally 2 layers

24. Super super PMTs New PMTs : super super bialkali Photocathode CENBG test Photonis PMTs and UCL test Hamamatsu PMTs QE : 32% -> 42 % => resolution : 8 (7) % -> 7 (6) % we are very optimistic for the 7% goal !!!

25. Conclusions • Very good results obtained from 2 teams on medium size container : LS is very promising • First results on large size container showed unexpected bad resolution,incoming new measurements (in both Kiev and Bordeaux) • Very good uniformity of light emission/collection measured in both labs • Experimental and simulation work on the optimization of light collection on sides : geometry, diffusion/reflection … in order to improve resolution • High QE PMTs will do a large part of the work • We are thinking about the container design for SuperNemo