Tracking (wire chamber)

Shield radon, neutron,

Source foil (40 mg/cm2)

Scintillator + PMT

2 modules 23 m2 → 12 m2

Background < 1 event / month

(164 s)

(300 ns)

232Th

212Bi(60.5 mn)

208Tl(3.1 mn)

212Po

208Pb(stable)36

%

238U

214Bi(19.9 mn)

210Tl(1.3 mn)

214Po

210Pb22.3 y0.

021%

Bi-Po Process

R&D BiPo DETECTOR

To measure the purity in 208Tl and 214Bi of the source foils before the installation in SuperNEMO

Goal: To measure 5 kg of foils (12 m2, 40 mg/cm2) in 1 month with a sensitivity of:

208Tl < 2 Bq/kg and 214Bi < 10 Bq/kg

delay

e

Q(214Bi)=3.2 Me

Tracking (wire chamber)

Shield radon, neutron,

Source foil (40 mg/cm2)

Scintillator + PMT

2 modules 23 m2 → 12 m2

Background < 1 event / month

(164 s)

(300 ns)

232Th

212Bi(60.5 mn)

208Tl(3.1 mn)

212Po

208Pb(stable)36

%

238U

214Bi(19.9 mn)

210Tl(1.3 mn)

214Po

210Pb22.3 y0.

021%

Bi-Po Process Q (212Bi) = 2.2 MeV

e

e prompt

T1/2 ~ 300 ns Edeposited ~ 1 MeV

Delay

R&D Detecteur BiPo

To measure the purity in 208Tl and 214Bi of the source foils before the installation in SuperNEMO

Goal: To measure 5 kg of foils (12 m2, 40 mg/cm2) in 1 month with a sensitivity of:

208Tl < 2 Bq/kg and 214Bi < 10 Bq/kg

With 5 kg of 82Se source foil (~ 12 m2, 40 mg/cm2)

50 (e-, delay ) 212Bi decays / month2 Bq/kg of 208Tl

3 events / month ~ 6%

Possible design

Two modules, each module 2 x 3 m2

Calorimeter:

2 x 150 PMTs + Scint. Blocks 2 x 20 x 20 cm2

15 scint. Bars 2 m long, 2 x 20 cm2

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)

T0 electron(trigger)

40 ns < Tdelay < 130 ns 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

e-

Prompt e T0

Delay , T1 ~ 300 ns

e-

Prompt e T0

Prompt e T0

Bulk contamination

Bkg event rejected

Surface contamination

No rejection

e-

Prompt e T0

Delay , T1 ~ 300 ns

e-

Prompt e T0

Prompt e T0

Bulk contamination

Bkg event rejected

Surface contamination

No rejection

Origin of backgrounds

Two prototypes to study the level of background

surface contamination of 208Tl on the entrance surface of the lower scintillator

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

Prototype BiPo-2

Proto 2: Jun. 2006 – Jun. 2007

1 x 1 m2 → 25 x 2 PMTs (20 x 20 cm2)

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: 212Bi electron must cross the material

e

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