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 ee Q  ( 214 Bi)=3.2 Me

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 ee 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

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

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 ee  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

Origin of backgrounds Two prototypes to study the level of background surface contamination of 208 Tl on the entrance surface of the lower scintillator

Prototype BiPo-1 end 2005 – Jun « 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 nm external Au for cleaning

Prototype BiPo-2 Proto 2: Jun – Jun x 1 m 2 → 25 x 2 PMTs (20 x 20 cm 2 )

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 ee  Final design must be studied depending on what we want to measure The detector could be installed in Canfranc ?…