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BiPo detector

BiPo detector. Planar detector To measure ultra low contaminations of 208 Tl and 214 Bi of thin double beta source foils. Xavier Sarazin Laboratoire de l’Accélérateur Linéaire ORSAY Joint Annual Meeting of N4 IDEA and N6 ENTApP/WP1 Blaubeuren, July 1-5, 2007. 238 U. 214 Po.

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BiPo detector

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  1. BiPo detector Planar detector To measure ultra low contaminations of 208Tl and 214Bi of thin double beta source foils Xavier Sarazin Laboratoire de l’Accélérateur Linéaire ORSAY Joint Annual Meeting of N4 IDEA and N6 ENTApP/WP1 Blaubeuren, July 1-5, 2007

  2. 238U 214Po (164 ms) b 214Bi (19.9 mn) Detect the BiPo decay cascade: beta + delay alpha a 210Pb 22.3 y 0.021% 210Tl (1.3 mn) 232Th 212Po (300 ns) b 212Bi (60.5 mn) a 208Pb (stable) 36% 208Tl (3.1 mn) Objectives Measure the purity in 208Tl and 214Bi of the SuperNEMO bb source foils Goal: To measure10 m2of foils (40 mg/cm2) in 1 month with a sensitivity of: Bulk cont.: 208Tl < 2 mBq/kg and 214Bi < 10 mBq/kg Surface cont.: 208Tl < 0.25 mBq/m2 and 214Bi < 1.25 mBq/m2

  3. Ethreshold (e-) = 150 keV Ethreshold (a) = 1 MeV (= 40 keV deposited due to quenching factor) If hit in time > 40 keV in the opposite scint., event is rejected (to reject external bkg) Geant4 simulation of 40 mg/cm2 foil with uniform bulk contamination e = 6.5 % Experimentalapproach Sandwich of two low radioactive plastic scintillators Time topology signature: 1 hit + 1 delay hit e- time a ~300 ns for 212Bi (208Tl) ~ 164 ms for 214Bi

  4. Surface purity of the detector e- e- time time a a Surface cont. not rejected Bulk contamination rejected Origin of background Random Coincidence: Single counting rate t must be as small as possible !!! Requirements: t1t2 ~ 0.1 Hz for 208Tl t1t2 ~ 0.04 Hz for 214Bi e- time e- t1: e- > 150 keV t2: a > 1 MeV (Escint>40 keV)

  5. Two possible designs to be studied in R&D • BiPo-1: Direct readout • BiPo-2 Multilayers scintillators plates with lateral readout

  6. Prototype BiPo-1 • Goal of this prototype: Background measurement • Random coincidence from single counting rate • Surface purity in 212Bi, 214Bi on the entrance surface of the scint. Capsules BiPo-1 PM 5” • Surface of scintillators: • scintillator blocs: 20 x 20 x 1 cm • Spottering of very thin layer of ultrapure aluminium on the surface of the scintillators: • e = 200 nm of ultrapure Al • We use NEMO-3 equipments • (radiopure 5” PMTs, radiopure scintillator, etc…) 8 capsules running since 29 June 2007 in Modane = 0.32 m2 20 caspules will be running end of 2007 = 0.8 m2 Mathieu Bongrand (LAL Orsay)

  7. Preliminary results of BiPo-1 • 2 capsules running during 11.3 days in Canfranc • 0 BiPo events detected with delay time < 1 ms • 1 BiPo “random coincidence” events (1ms <delay time<2 ms) for 1 expected coincidence A(212Bi  212Po) < 29 µBq/m2 A(208Tl) < 15 µBq/m2 Mathieu Bongrand (LAL Orsay)

  8. Foil installed inside the first capsule BiPo-1 • ~ 10 BiPo events detected / day • Ac(212Bi) = 0.21 ± 0.03 Bq/kg • Excellent Aggreement • Valid the method • Valid the MC Geant4 • calculation of the efficiency Calibration of BiPo-1 • Standard aluminium foil 40 mg/cm2 (like SuperNEMO), • 20 x 20 cm2 • Foil measured by HPGe in CENBG Bordeaux • Ac(212Bi) = 0.19 Bq/kg Mathieu Bongrand (LAL Orsay)

  9. Phoswich Technique for BiPo-1 10 mm slow scintillator for e- detection Very thin 300 mm fast scintillator for alpha detection e- a b/a identification • Should reduce strongly the single counting rate (only 300 mm thickness) Especialy for 214Bi -> 214Po measurement • b hit and delay a hit can be detected in the same scintillator block • Efficiency increased to 9.5% (instead of 6.5%) • Should be able to measure surface radiopurity of thick materials 1 prototype in construction to be installed in a BiPo-1 capsule: fast scint: BC408 (300 mm), slow scint.: BC444 (Nadia Yahlali from IFIC Valencia)

  10. e- a BiPo-2 Prototype Naked large scintillator plate polished by mold production Scint. light collected by total internal reflectivity Advantages: compact and light detector BiPo-2 prototype: scint. Plate 75 x 75 cm2 Setup under installation this week in Orsay Goal: - Energy threshold - Spatial resolution - Crosstalk Installation of the setup in Modane end of 2007 Jeremy Argyriades (LAL Orsay)

  11. Conclusion • End 2007: BiPo-1 (0.8m2) and BiPo-2 (0.56m2)running in Modane • Preliminary sensitivity BiPo-1 with 0.08 m2 • A(208Tl) < 15 mBq/m2 • It will provide two first little BiPo detectors of ~ 1.4 m2 (600 g foil) • Expected sensitivity for the measurement of 600 g of Se bb SuperNEMO source foil in 6 month • A(208Tl) < 3 mBq/kg • Phoswich technique is under development • should reduce strongly the external bkg • could provide a BiPo detector able to measure the surface of thick material (Cupper frame etc…) • BiPo could also measure Radon purity of SuperNEMO gas with a sensitivity • A(Radon) < 100 mBq/m3 • Will be able to test it with prototype… • Construction of BiPo detector could start in 2008 after prototypes results…

  12. Shield Test Facility 20 BiPo-1 capsules + 75 x 75 cm2 BiPo-2 prototype Shield Test Facility: internal volume 1.45 m x 1.45 m x 1.05 m Radon-tight tank (pure iron) Free radon air 105 cm Pure Lead shield (13 tons) 145 x 145 cm

  13. BACK SLIDES

  14. Random coinc for 10 m2 1 microsec: 1 count/month 500 microsec: 500/30 ~ 15 count/day 100 microBq -> 8.6 BiPo decays/day -> ~4 BiPo events/day Sensitivity ~ A < 75 microBq/m3/day

  15. quenching a energy (MeV) Fit between 40 and 130 ns : T 1/2 = (212 +/- 65) ns ~ 300 ns expected Qb ~ 2.2 MeV Time delay between a and electron (in ns) electron energy (MeV) Analysis of such background in NEMO-3 data 1642 events observed in 1 year of data Factor 10 Too High !!! If all comes from mylar: 2.5 mBq/kg a 40 ns < Tdelay < 130 ns e- T0 electron (trigger) Xavier Sarazin (LAL Orsay), Canfranc Scientific Council, 06 July 2006

  16. e- a e ~ 0.25a escapefrom the foil with a energy > 1 MeV (~ 50 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 e ~ 0.5 e- goes up e ~ 0.5 a goes down Total efficiency ~ 6% Xavier Sarazin (LAL Orsay), Canfranc Scientific Council, 06 July 2006

  17. Measurement of the quenching factor 241Am α source, peak at 5.6 MeV Light in a scintillator detected by a PMT Successive mylar foils to decrease the α energy /19

  18. Measurement of the quenching factor @ 1 MeV QF = ~25 40 keV threshold for e- = ~1MeV threshold for α /19

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