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)


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)


Location

• Modane Underground Laboratory

• at the French-Italian border

• under 1800 m of rock

• 4800 m.w.e.


TGV I

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

Energy resolution (2.6 – 3.3)keV @ 60Co


TGV I

open cryostat assembled cryostat, PAs


TGV I

cryostat surrounded by Cu shielding


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)


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(


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


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


TGV II spectrometer

Dewar

cryostatPbCu

borated polyethylene

PA

SM

1m


TGV II

pedestal open cryostat


TGV II

assembled cryostat, PAs


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)


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


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


Pulse shape analysis (example)

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

Q

E

electrons

gammas

Compton edge


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)


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


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)


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


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

• 2033 hours, 158382662 events


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



• 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


• present situation:

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


• next steps (2005 – 2006):

• enriched Cd purification

• Cd-nat. data final procession

• measurement with 48Ca


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

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