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Tracking (wire chamber) Shield radon, neutron, Source foil (40 mg/cm 2 ) Scintillator + PMT 2 modules 2 3 m 2 → 12 m 2 Background < 1 event / month (164 s) (300 ns) 232 Th 212 Bi (60.5 mn) 208 Tl (3.1 mn) 212 Po 208 Pb (stable) 36% 238 U 214 Bi (19.9 mn) 210 Tl (1.3 mn) 214 Po 210 Pb 22.3 y 0.021% Bi-Po Process R&D BiPo DETECTOR To measure the purity in 208 Tl and 214 Bi of the source foils before the installation in SuperNEMO Goal: To measure 5 kg of foils (12 m 2, 40 mg/cm 2 ) in 1 month with a sensitivity of: 208 Tl < 2 Bq/kg and 214 Bi < 10 Bq/kg delay ee Q ( 214 Bi)=3.2 Me
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Tracking (wire chamber) Shield radon, neutron, Source foil (40 mg/cm 2 ) Scintillator + PMT 2 modules 2 3 m 2 → 12 m 2 Background < 1 event / month (164 s) (300 ns) 232 Th 212 Bi (60.5 mn) 208 Tl (3.1 mn) 212 Po 208 Pb (stable) 36% 238 U 214 Bi (19.9 mn) 210 Tl (1.3 mn) 214 Po 210 Pb 22.3 y 0.021% Bi-Po Process Q ( 212 Bi) = 2.2 MeV ee e prompt T 1/2 ~ 300 ns E deposited ~ 1 MeV Delay R&D Detecteur BiPo To measure the purity in 208 Tl and 214 Bi of the source foils before the installation in SuperNEMO Goal: To measure 5 kg of foils (12 m 2, 40 mg/cm 2 ) in 1 month with a sensitivity of: 208 Tl < 2 Bq/kg and 214 Bi < 10 Bq/kg
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With 5 kg of 82 Se source foil (~ 12 m 2, 40 mg/cm 2 ) 50 (e-, delay ) 212 Bi decays / month 2 Bq/kg of 208 Tl 3 events / month ~ 6% Possible design Two modules, each module 2 x 3 m 2 Calorimeter: 2 x 150 PMTs + Scint. Blocks 2 x 20 x 20 cm 2 15 scint. Bars 2 m long, 2 x 20 cm 2 Tracking: 4 layers of Geiger drift cells Magnetic field suitable to reject external e Room needed: 4 x 5 m2 (with shield) + clean room beside the detector
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Fit between 40 and 130 ns : T 1/2 = (212 +/- 65) ns ~ 300 ns expected Time delay between and electron (in ns) quenching energy (MeV) Q ~ 2.2 MeV electron energy (MeV) T 0 electron (trigger) 40 ns < T delay < 130 ns ee 1642 events obvserved in 1 year of data If all comes from mylar: 2.5 mBq/kg Analysis of such events in NEMO-3 data
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Origin of backgrounds Two prototypes to study the level of background surface contamination of 208 Tl on the entrance surface of the lower scintillator
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Prototype BiPo-1 end 2005 – Jun. 2006 « screan » to stop scintillation light Naked scintillator 20x 20 x 2cm Light guide PMT 5" NEMO3 1 cm bored Polyethylen lead Air outlet + cables Radon-free air Radon-tight enveloppe 10 cm bored Polyethylen We will use NEMO-3 equipments (5” PMTs, scintillator, etc…) Surface of scintillators: Spottering of very thin layer of metal on the surface of the scintillators: 100 nm internal Al for reflecting + 100 nm external Au for cleaning
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Prototype BiPo-2 Proto 2: Jun. 2006 – Jun. 2007 1 x 1 m 2 → 25 x 2 PMTs (20 x 20 cm 2 )
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BiPo detector may become a new low background detector (like HPGe generation…) to measure 214Bi and 208Tl purity of thin materials (volume or surface) foils for SuperNEMO Capton foils for GERDA Cables ? etc… Limitation of the thickness: 212 Bi electron must cross the material ee Final design must be studied depending on what we want to measure The detector could be installed in Canfranc ?…
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