Measurement of EC /EC process of 106 Cd in the experiment TGV II

1. Measurement of EC/EC process of 106Cdin the experiment TGV II I.Štekl, P.Čermák, P.Beneš Institute of Experimental and Applied Physics, CTUin Prague V.B.Brudanin, V.G.Egorov, N.I.Rukhadze, A.Kovalík, Ts.Vylov et al. Joint Institute of Nuclear Research, Dubna Ch.Briancon CSNSM Orsay F.Šimkovic Comenius University, Bratislava • Short review of TGV I • Double electron capture – present results of theory and experiments • Experimental setup TGV II • Methods of background suppresion • Preliminary results of measurement with enriched 106Cd IDEA meeting, Zaragoza, 7.-8.11.2005

2. TGV I : 48Ca: ~ 1.35 x 1022 atoms (1.08 g) open cryostat assembled cryostat, PAs

3. TGV I cryostat surrounded by Cu shielding

4. TGV I results (48Ca) Published in Nuclear Physics A700(1-2) (2002) 17-24

5. purpose: TGV II • to improve 48Ca result obtained by TGV I • to investigate  processes in 106Cd (to focus on 2nEC/EC channel) 106Cd: 2nEC/EC: 48Ca: 2nbb:

6. Theorethical results for EC/EC mode: 0+g.s. - T1/2: 1.5 x 1022 y; 4.4 x 1021 y; 8.7 x 1020 y; 1 x 1020 y; 9 x 1019 y 0+1 - T1/2: 1.1 x 1024 y; 1.0 x 1023 y; 3.4 x 1021 y; (2.2-3.9 x 1021 y) Experimental results for EC/EC mode: 0+ g.s. – T1/2 : > 5.8 x 1017 y; > 1.5 x 1017 y 0+ 1 – T1/2 : > 6.2 x 1018 y; > 7.3 x 1019 y

7. Double Beta Spectrometers TGV

8. General view of TGV II setup Copper > 20 cm Airtight box Lead > 10 cm Polyethylene filled with boron 16 cm

9. Detector part of the TGV II 32HPGe planar detectors 60 mm x 6 mm with sensitive volume: 20.4 cm2 x 6 mm Total sensitive volume: 400 cm3 Total mass of detectors: 3 kg Total area of samples : 330 cm2 Total mass of sample(s) : 10  25 g Total efficiency : 50  60 % E-resolution : 3  4 keV@ 60Co LE-threshold : 4050 keV (5  6 keV) Double beta emitters - 16 samples of 48Ca (10 g) : 24 g CaF2 + CH2 ( 75 mg / cm2 ) - 12 samples of 106Cd: 10 10 g 106Cd(~ 50 µm ) U+Th<0.1 ppb

11. TGV II pedestal open cryostat

12. TGV II assembled cryostat, PAs

16. Background suppression • Passive shielding • Construction of the detector TGV II • 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)

17. Background suppression • 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

18. Data processing 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

19. Pulse shape analysis (48Ca) Current • based on difference between interaction of e- and g-rays with detector crystal • point of interaction - charge collection time - pulse shape - integrated charge => E-Q spectrum • ability to suppress g-rays by factor 2-3 Q1 g Q2 e 0 10 Time, ns 20 strobe Q (integrated charge) g e Amplitude (energy)

20. Pulse shape analysis (example) Q Compton edge gammas electrons E E-Q spectrum, sources: 207Bi + 60Co

21. Data processing 2) Cd setup • interest in low energy region (19 – 23) keV • additional source of background are microphonic and electronic noise – filtering is done using two different shaping times during the processing of the signal

22. Suppression of microphonic noise Low frequency (microphonic) 12µs 4µs

23. Microphonic noise suppression (example) start: March 2002, stop: July 2002; result presented: May-July 2002, duration 1596 hours • no selection • microphonic noise cut • coincidence with neighboring detectors • coincidence + energy window (19-25) keV

24. Summary of finished activities and present status: • two different setups (for 106Cd and 48Ca) were tunned • detector TGV II is placed in Modane underground laboratory • standard passive methods to suppress the background • suppression of microphonic background • pulse-rise time analysis • measurements of background were finished • TGV spectrometer is running in Cd setup with enriched 106Cd !!!! Programme of background measurements: • without any foils • with foils made of natural Cd (16 foils, Nov. 2004 – Jan. 2005, 14.5 gr.) Programme of EC/EC measurements: • Three portions of enriched 106Cd – two of them included 113mCd • Last one is pure – 12 foils, total mass = 9.948 gr., enrichment = 80% (inside of TGV II – 12 foils of enriched 106Cd, 4 foils of natural Cd, beginning of measurement – Febr. 2005)

25. Background measurement Sources of natural Cd in the TGV II spectrometer (16 foils; 14.5 gr.; 743+161 hours = 903 hours)

26. Background measurement Natural Cd (4 foils of natural Cd)+ all kinds of backgr.suppr. – 3736 hours (February 2005 - July 2005)

27. Measurement of EC/EC decay Enriched Cd (12 foils), all kinds of backg. suppr. – 3736 hours (February 2005- July 2005)

28. KX(Pd) and KX(Cd) in 106Cd

29. 106Cd, 10 g, 3000 h Pd Cd

30. 19 keV - 22 keV Enriched Cd (12 foils), all kinds of backg.suppr. – 3736 hours (February 2005 - July 2005)

31. total weight of natural Cd foils = 3.151 gramms (events for natural Cd were recalculated for the weight of enriched Cd) 2nEC/EC (g.s. -> g.s.) “signal” on the level 2.5 s

32. Results 0+ 1138 2νEC/EC/1138 T1/2 ≥ 5.3 x 1019 y (90%CL) 2+ 512 2νβ+EC/512 T1/2 ≥ 5.8 x 1019 y (90%CL) 2νEC/EC/512 T1/2 ≥ 2.1 x 1019 y (90%CL) 2νEC/EC (0+→0+,g.s.) T1/2 ≥ 5.6 x 1019 y (90%CL) 2νβ+EC (0+→0+,g.s.) T1/2 ≥ 4.1 x 1019 y (90%CL)

33. Summary: • TGV II is nice equipment for measurement of special bb modes • it could be first direct measurement of 2nEC/EC mode (big shift of half-life) • we will continue with 106Cd as minimum one year • TGV II as part of EU project (to construct the second detector; longer time of measurement; to add special isotopes such as 106Cd into bank of EU isotopes – production with 116Cd)