for tgv collaboration: jinr dubna, russia ieap ctu prague, czech republic csnsm orsay, france

Experiment TGV IIMulti-detector HPGe telescopic spectrometer

for the study of double beta processes of 106Cd and 48Ca

For TGV collaboration:

JINR Dubna, RussiaIEAP CTU Prague, Czech Republic

CSNSM Orsay, FranceRRC - Kurchatov Institute Moscow, Russia

CU Bratislava, Slovakia

P. Cermak, Rez near Prague, December 2004

P. ČermákCzech Technical University, Prague

Outline● TGV I TGV II● Description of TGV II● Background suppression● Data processing, results of

background measurements● Conclusion, near future

The Aim:

To study rare processes - double beta processes of 106Cd and 48Ca (double-beta decay, double electron capture)

P. Cermak, Rez near Prague, December 2004

TGV

• Telescope Germanium Vertical (stack of 32 HPGe detectors in common cryostat)

• aims at the study of double beta processes of 106Cd and 48Ca (double-beta decay, double electron capture)

• started in 2000

• located in Modane Underground Laboratory (France)

P. Cermak, Rez near Prague, December 2004

Location

• Modane Underground Laboratory

• at the French-Italian border

• under 1800 m of rock

• 4800 m.w.e.

P. Cermak, Rez near Prague, December 2004

TGV I

16 HPGe detectors of planar type, diameter 40mm, thickness 6mm

Energy resolution (2.6 – 3.3)keV @ 60Co

P. Cermak, Rez near Prague, December 2004

TGV I

open cryostat assembled cryostat, PAs

P. Cermak, Rez near Prague, December 2004

TGV I

cryostat surrounded by Cu shielding

P. Cermak, Rez near Prague, December 2004

Sources in TGV I spectrometer

● 8 foils (48Ca)

● 8 foils (Ca natural)

48Ca foil: 80% CaCO3 (enriched 77.8%) + 20%

polyvinyl formal

● Dimensions: (32.5 x 32.5)mm each

● Thickness: 41 mg/cm2 (48Ca)

45 mg/cm2 (Ca natural)

● 48Ca: ~ 1.35 x 1022 atoms (1.08 g)

P. Cermak, Rez near Prague, December 2004

TGV I results (48Ca)

yT 193.33.1

22/1 10)2.4(

)%90(105.1 2102/1 CLyT

yT 193.33.1

22/1 10)2.4(

P. Cermak, Rez near Prague, December 2004

TGV II• to improve 48Ca result

obtained by TGV I

• to investigate processes in 106Cd (to focus on EC/EC channel)

),(22 10646

10648 raysXPdCde e

purpose:

2EC/EC:

106Cd:

keVEkeVkeV XECEC 5.235.18:ROI,2778Q /

2:

48Ca:

)(2~24822

4820 eTiCa e

MeVEMeVkeV e 2.47.2:ROI,4272Q

P. Cermak, Rez near Prague, December 2004

Basic parameters

Stack of 32 HPGe planar detectors:

diameter 60mm

thickness 6mm

sensitive area (each detector) ~ 20cm2

total area of samples ~ 330cm2

total mass of samples ~ 10g

energy resolution (FWHM) ~ 3keV @ 60Co

low energy threshold down to 5keV

P. Cermak, Rez near Prague, December 2004

TGV II spectrometer

Dewar

cryostatPbCu

borated polyethylene

PA

SM

1m

P. Cermak, Rez near Prague, December 2004

TGV II

pedestal open cryostat

P. Cermak, Rez near Prague, December 2004

TGV II

assembled cryostat, PAs

P. Cermak, Rez near Prague, December 2004

Background suppression (1)

• Passive shielding• Construction• Electronics

● Passive shieldings– Modane Underground Laboratory– Pb + Cu, airtight box against radon (antiradon

system, 15Bq/m3 → ~ mBq/m3 , October 04), anti-neutron shielding (made of borated polyethylene)

P. Cermak, Rez near Prague, December 2004

Background suppression (2)

● Construction– radiopure materials– minimization of amount of construction

materials● Electronics

– telescopic construction (double coincidences from neighboring detectors)

– time information about events (date, time between coinc. events)

– pulse rise time analysis– double-shaping selection of low energy

eventsP. Cermak, Rez near Prague, December 2004

Data processing (1)

• DAQ program – RT Linux remotely operated and controlled

• data are recorded event-by-event, processed offline

1) Ca setup• interest in a region (2.7 - 4.2) MeV

• utilization of a technique for a distinguishing between electrons and -rays based on pulse shape analysis

P. Cermak, Rez near Prague, December 2004

Pulse shape analysis (principle)

Current

Time, ns

Q2

Q1

e10 200

strobe

Q (integrated charge)

e

Amplitude (energy)

• based on difference between interaction of e- and -rays with detector crystal

• point of interaction - charge collection time - pulse shape - integrated charge => E-Q spectrum

• ability to suppress -rays by factor 2-3

P. Cermak, Rez near Prague, December 2004

Pulse shape analysis (example)

E-Q spectrum, sources: 207Bi + 60Co

Q

E

electrons

gammas

Compton edge

P. Cermak, Rez near Prague, December 2004

2) Cd setup• interest in low energy region (18.5 – 23.5)

keV

• additional source of background are microphonic and electronic noise – filtering is done using two different shaping times during the processing of the signal

Data processing (2)

P. Cermak, Rez near Prague, December 2004

Microphonic noise suppression (principle)

• events in low energy region – up to 100keV

• utilization of two amplifiers with different shaping time

• selection by means of a 'matrix' – Eshort vs. Elong

ROI

P. Cermak, Rez near Prague, December 2004

Matrices example

TGV II electronics (Cd setup)

• Double – shaping method

• Multiplexed channels

• MT – Master Trigger block (input register, gate generator, veto generator)

• N2 filling flag

• no selection

start: March 2002, stop: July 2002; result presented:May-July 2002, duration 1596 hours

• coincidence + energy window (19-25) keV

• coincidence with

neighboring

detectors

• microphonic

noise cut

Microphonic noise suppression (example)

P. Cermak, Rez near Prague, December 2004

Runs overview (year 2004)

1. Cd background (December 03 – February 04)

• 1363 hours, 14312946 events

• no foils

2. Enriched Cd, type I (March 04 – May 04)

• 1768 hours, 16531047 events

• 13x 106Cd foil, 3x Cd-nat. foil

2. Enriched Cd, type II (May 04 – June 04)

• 328 hours, 3515849 events

• 12x 106Cd foil, 4x Cd-nat. foil

3. Enriched Cd, type II (June 04 – October 04)

• 2033 hours, 158382662 events

• 12x 106Cd foil, 4x Cd-nat. foil

4. Enriched Cd, type II (November 04 – now)

• 16x Cd-nat. foil

Conclusion, near future (1)

• background for 48Ca (preliminary – 1 month run):

– 45 ev./year in (2.7-4.2)MeV region – expected effect: 35 ev./year

• both setups were assembled and tested• basic runs needed for background

determination (both for 48Ca and 106Cd setup) were performed

P. Cermak, Rez near Prague, December 2004

Conclusion, near future (1)

• background for 106Cd (preliminary – 3 months run):- 44 ev./year in (19-25)keV region- expected effect: 42 ev./year (T1/2 ~ 1020 y, g.s. → g.s., enriched Cd)

• natural Cd

- estimation of T1/2 ~ 1018 y, g.s. → g.s.

- estimation of T1/2 ~ 1019 y, g.s. → 2+1

P. Cermak, Rez near Prague, December 2004

• present situation:

TGV II is running in Cd setup with Cd-nat.

Conclusion, near future (2)

• next steps (2005 – 2006):

• enriched Cd purification

• Cd-nat. data final procession

• measurement with 48Ca

P. Cermak, Rez near Prague, December 2004