Experiment TGV II Multi-detector HPGe telescopic spectrometer for the study of double beta processes of 106 Cd and 48 Ca For TGV collaboration: JINR Dubna, Russia IEAP CTU Prague, Czech Republic CSNSM Orsay, France RRC - Kurchatov Institute Moscow, Russia CU Bratislava, Slovakia P. Cermak, Rez near Prague, December 2004 P. Čermák Czech 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 106 Cd and 48 Ca (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 106 Cd and 48 Ca (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 – 60 Co P. Cermak, Rez near Prague, December 2004

TGV I open cryostatassembled 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 ( 48 Ca) ● 8 foils (Ca natural) 48 Ca foil: 80% CaCO 3 (enriched 77.8%) + 20% polyvinyl formal ● Dimensions: (32.5 x 32.5)mm each ● Thickness: 41 mg/cm 2 ( 48 Ca) 45 mg/cm 2 (Ca natural) ● 48 Ca: ~ 1.35 x atoms (1.08 g) P. Cermak, Rez near Prague, December 2004

TGV I results ( 48 Ca) P. Cermak, Rez near Prague, December 2004

TGV II to improve 48 Ca result obtained by TGV I to investigate  processes in 106 Cd (to focus on EC/EC channel) purpose: 2 EC/EC: 106 Cd: 2  : 48 Ca: P. Cermak, Rez near Prague, December 2004

Basic parameters Stack of 32 HPGe planar detectors: diameter 60mm thickness 6mm sensitive area (each detector) ~ 20cm 2 total area of samples~ 330cm 2 total mass of samples~ 10g energy resolution (FWHM)~ 60 Co low energy threshold down to 5keV P. Cermak, Rez near Prague, December 2004

TGV II spectrometer Dewar cryostat Pb Cu borated polyethylene PA SM 1m P. Cermak, Rez near Prague, December 2004

TGV II pedestalopen 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/m 3 → ~ mBq/m 3, 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 events P. 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 ( ) 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  e 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: 207 Bi + 60 Co 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' – E short vs. E long 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) N 2 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, events no foils

2.Enriched Cd, type I (March 04 – May 04) 1768 hours, events 13x 106 Cd foil, 3x Cd-nat. foil

2.Enriched Cd, type II (May 04 – June 04) 328 hours, events 12x 106 Cd foil, 4x Cd-nat. foil 3.Enriched Cd, type II (June 04 – October 04) 2033 hours, events 12x 106 Cd foil, 4x Cd-nat. foil 4.Enriched Cd, type II (November 04 – now) 16x Cd-nat. foil

Conclusion, near future (1) background for 48 Ca (preliminary – 1 month run): – 45 ev./year in ( )MeV region – expected effect: 35 ev./year both setups were assembled and tested basic runs needed for background determination (both for 48 Ca and 106 Cd setup) were performed P. Cermak, Rez near Prague, December 2004

Conclusion, near future (1) background for 106 Cd (preliminary – 3 months run): - 44 ev./year in (19-25)keV region - expected effect: 42 ev./year (T 1/2 ~ y, g.s. → g.s., enriched Cd) natural Cd - estimation of T 1/2 ~ y, g.s. → g.s. - estimation of T 1/2 ~ y, g.s. → 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 48 Ca P. Cermak, Rez near Prague, December 2004