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The SuperNemo BiPo detector

The SuperNemo BiPo detector. Jean-stephane Ricol CENBG - CNRS VIeme rencontres du Vietnam Hanoi August 2006. Motivation. Current bb0n experiment sensitivity on neutrino effective mass ~ 0.2-1 eV SuperNemo aimed sensitivity < ~ 50 meV

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The SuperNemo BiPo detector

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  1. The SuperNemo BiPo detector Jean-stephane Ricol CENBG - CNRS VIeme rencontres du Vietnam Hanoi August 2006

  2. Motivation Current bb0n experiment sensitivity on neutrino effective mass ~ 0.2-1 eV SuperNemoaimed sensitivity < ~ 50 meV T1/2 (82Se 150Nd) > ~ 1026 yrs - BG < 1 evt/100kg/yr High level of purification for the source foils Goal of the BiPo detector : Measure the contamination in 208Tl and 214Bi of the bb source foilsbefore the installation in SuperNEMO 5 kg of source (12 m2, 40 mg/cm2) in 1 month with a sensitivity of 208Tl < 2 µBq/kg and 214Bi < 10 µBq/kg

  3. Bi-Po Process 238U 214Po e- Scintillators + PMT T0, Qb(214Bi)=3.2 MeV (164 ms) b 214Bi (19.9 mn) a 210Pb 22.3 y 0.021% Tracking (wire chamber) a (delay 164µs) 210Tl (1.3 mn) Source foil (40 mg/cm2) 232Th 212Po (300 ns) b 212Bi (60.5 mn) a 208Pb (stable) 36% e- 208Tl (3.1 mn) BiPo detection Use the Bi-Po coincidence in the decay chain

  4. Bi-Po Process 238U 214Po e- Scintillators + PMT T0, Qb(214Bi)=3.2 MeV (164 ms) b 214Bi (19.9 mn) a 210Pb 22.3 y 0.021% Tracking (wire chamber) a (delay 300 ns) 210Tl (1.3 mn) Source foil (40 mg/cm2) 232Th 212Po (300 ns) b 212Bi (60.5 mn) a 208Pb (stable) 36% e- 208Tl (3.1 mn) BiPo detection Use the Bi-Po coincidence in the decay chains a delay T1/2 ~ 300 ns Drift time ~ µsec / cm 212Po a cant be detected in the wire chamber  need a dedicated detector

  5. Bi-Po Process 238U 214Po e- Scintillators + PMT T0, Qb(212Bi)=2.2 MeV (164 ms) b 214Bi (19.9 mn) a 210Pb 22.3 y 0.021% Tracking (wire chamber) 210Tl (1.3 mn) Source foil (40 mg/cm2) 232Th 212Po (300 ns) b a Scintillator + PMT 212Bi (60.5 mn) a 208Pb (stable) 36% e- 208Tl (3.1 mn) BiPo detection Use the Bi-Po coincidence in the decay chains a adelay T1/2 ~ 300 ns Edeposited ~ 1 MeV

  6. e- e ~ 0.5 e- goes up a e ~ 0.5 a goes down e ~ 0.25a escapes from the foil with a energy > 1 MeV (~150 keV for energy deposited in the scintillator due to the quenching) Efficiency Thickness of the foil (mg/cm2) Initial energy of the a: E = 8.750 MeV Efficiency Total efficiency ~ 6%

  7. Scintillator plate Thickness=1cm (as MOON-1 prototype) Foil to be measured Gamma tagging 0.8m g e- a g Two possible designs studied in R&D • Multilayer scintillator plates without tracking • Alpha scintillator with electron tracking detector • e- tagging • Efficiency x 4 • Compact geometry & less channels Measurement of 214Bi is not possible (214Po T1/2 = 164 µs  high random coincidence bkg)  Radon emanation detector developed by Heidelberg

  8. Technique can be very usefull for a and e- identification with the multi-layers design e- a Parallel R&D : Ultra thin scintillator Ultra-thin scintillating detector (plastic or fiber) for a measurement and e- tagging (e- cross the a calorimeter) • Advantages: • e ~ 25% Can be used in both designs e- a Foil to be measured

  9. Parallel R&D : Ultra thin scintillator Thickness of UTS : All a detected if. > 90 µm Optimal for e- ~200-500 µm Crossing efficiency ~ 65-50% DE ~ 100-200 keV • Material possibilities : • Plastic : Kharkov produce 2m long x few cm large x 200 µm • Fibers : Bicron produces scint. fiber 250 µm (square or round section) To be tested : Light yield ? Radiopurity ?

  10. Ultra Low Background Detector 5 kg of 82Se source foil (~ 12 m2, 40 mg/cm2) 50 (e-, delay a) 212Bi decays / month 2 mBq/kg of 208Tl 3-12 decays / month e ~ 6-25 % Background < 1 event/month is required ! Ultra high radiopurity required for the surface of the scintillator

  11. Prompt e-, T0 Prompt e-, T0 e- e- a a delay a, T1/2 ~ 300 ns Prompt e-, T0 Main origin of background Surface contamination of 208Tl on the entrance surface of the lower scintillator Bulk contamination Surface contamination Bkg event NOT rejected Bkg event rejected e- <deposited energy> ~ 50 keV in 100 µm of scintillator

  12. 40 ns < Tdelay < 130 ns a e- T0 electron (trigger) Dt between a and e- (in ns) electron energy (MeV) a energy (MeV) Fit between 40 and 130 ns : T 1/2 = (212 +/- 65) ns ~ 300 ns expected Qb ~ 2.2 MeV quenching Analysis of such BG in NEMO-3 data 1642 events observed in 1 year of data Factor 10 Too High !!! If all comes from mylar wrapping : 2.5 mBq/kg

  13. Capsule BiPo-1 PM 5” e =1 cm Prototype BiPo-1 • Goal of this prototype: Background measurement • Random coincidence from single counting rate of the scint. + PMT • scintillator blocs: 20 x 20 x 1 cm • Surface contamination 212Bi on scintillator entrance surface Surface treatment : Very thin layer e = 200 nm of ultrapure aluminium deposit on the scintillator surface NEMO-3 equipments: radiopure 5” PMTs, radiopure scintillators First capsule installed in Canfranc laboratory end of september 2006

  14. Up to 25 capsules can be installed in Phase I 1050 2000 300 1450 x 1450 2300 x 2300 Prototype BiPo-1 Shield Test Facility: external: 2.3 m x 2.3 m x 2 m internal: 1.45 m x 1.45 m x 1.05 m Radon-tight tank (pure iron) Free radon air Lead shield (13 tons) Water shield

  15. 70 cm Prototype BiPo-1 Phase II Bg measurement of multi layers design

  16. Conclusion • BiPo detector must reach a sensitivity of few µBq/Kg • Different designs are under study, they will be tested during 2007-2008 with first prototypes • The final BiPo detector is planned to be built and installed in the Canfranc laboratory in 2009

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