Problematika pozad v experimentech subjadern fyziky

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Present status of the experiment TGV II
I.tekl, P.Cermák, P.Bene Institute of
Experimental and Applied Physics, CTU in
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.imkovic 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
• Results of background measurement
• Preliminary results of measurement with enriched
  106Cd

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TGV I 48Ca 1.35 x 1022 atoms (1.08 g)
open cryostat
assembled cryostat, PAs
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TGV I
cryostat surrounded by Cu shielding
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TGV I results (48Ca)
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TGV II
purpose

• to improve 48Ca result obtained by TGV I
• to investigate ?? processes in 106Cd (to focus on
  2nEC/EC channel)

106Cd
2nEC/EC
48Ca
2nbb
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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 gt 5.8 x 1017 y gt 1.5 x 1017
y 0 1 T1/2 gt 6.2 x 1018 y gt 7.3 x 1019 y
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Double Beta Spectrometers

• TGV

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General view of TGV II setup
Copper gt 20 cm

Airtight box
Lead gt 10 cm
Polyethylene filled with boron 16 cm
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Detector part of the TGV II

• 32 HPGe 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 _at_ 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 )

UThlt0.1 ppb
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TGV II
pedestal
open cryostat
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TGV II
assembled cryostat, PAs
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Background suppression

• 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)

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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

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Data processing

• 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

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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 gt E-Q
• spectrum
• ability to suppress g-rays
• by factor 2-3

Q1
g
Q2
e
Time, ns
10
20
0
strobe
Q (integrated charge)
g
e
Amplitude (energy)
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Pulse shape analysis (example)
Q
Compton edge
gammas
electrons
E
E-Q spectrum, sources 207Bi 60Co
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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

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Suppression of microphonic noise
Low frequency (microphonic)
12µs
4µs
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TGV II electronics (Cd setup)

• Double shaping method
• Multiplexed channels
• MT Master Trigger block (input register, gate
  generator, veto generator)
• N2 filling flag

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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

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• 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

• 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)

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Cd measurements (2004 - )

• 13 samples (11.3 g) of 106Cd 3 samples (2.4 g)
  of Cd-nat.
  (Feb. 2004
  May 2004)
• 12 samples (10 g) of 106Cd (enrich.68) 4
  samples (3.2 g) of Cd-nat.
  
• (May 2004 Nov. 2004)
• 16 samples (14.5 g) of Cd-nat.
• (Nov.2004 Jan.2005)
• 12 samples (10 g) of 106Cd (enrich.75) 4
  samples of Cd-nat.
  
• (Feb.2005 - )

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106Cd (with 113mCd), 10 g, 1117h
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KX-rays from 113mCd
11/2-
0.2637
14y
113mCd
1/2- 0.39169
ß- 99.9
99.5 m
99
113mIn
1/2
0
9x1015y
113Cd
9/2 0
ß-
113In
Qß- 0.322
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Result of measurement without any sources in the
TGV II spectrometer (1343 hours)
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Result of measurement with sources of natural Cd
in the TGV II spectrometer (743161 hours 903
hours)
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Cd-nat. , 14.5 g, 903 h
SINGLE
2 COINC.
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Result of measurement with sources of natural Cd
in the TGV II spectrometer (3736 hours, up to
July 2005) total spectrum of single events
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Natural Cd all kinds of backgr.suppr. 3736
hours (up to July 2005)
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106Cd, 10 g, 3000 hours
1
KX(Cd)
Th
ThU
Th
Th
Th
Th
U
2
Th
511
Th
U
3
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KX(Pd) and KX(Cd) in 106Cd
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106Cd, 10 g, 3000 h
Pd
Cd
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Enriched Cd, single events 3736 hours (up to
July 2005)
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Enriched Cd, all kinds of backg. suppr. 3736
hours (up to July 2005)
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19 keV - 22 keV
Enriched Cd, all kinds of backg.suppr. 3736
hours (up to July 2005)
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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. -gt g.s.) signal on the level 2.5
s
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Results
0 1138
2?EC/EC/1138 T1/2 5.3 x 1019 y (90CL)
2 512
2?ßEC/512 T1/2 5.8 x 1019 y
(90CL) 2?EC/EC/512 T1/2 2.1 x 1019 y (90CL)
2?EC/EC (0?0,g.s.) T1/2 5.6 x 1019 y
(90CL) 2?ßEC (0?0,g.s.) T1/2 4.1 x 1019 y
(90CL)
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• Summary
• TGV II is nice equipment for measurement of
  special bb modes
• it could be first measurement of 2nEC/EC mode
  (big shift of half-life)
• we will continue with 106Cd as minimum one year
• 0nEC/EC study in the future (0nEC/EC-decay 0 ?
  0 transition should be accompanied by an
  emission of some additional particles in order to
  satisfy the energy-momentum conservation. It
  could be e.g. the internal electron-positron pair
  formation, emission of two photons in the final
  state and one real photon associated with the
  capture from the LI shell. This process has been
  not yet studied in details. The theoretical
  calculations as well as experimental measurements
  of 0nEC/EC-decay are, therefore, desirable.
  Recently, Sujkowski and Wycech pointed out that
  this process might be an important tool to search
  for Majorana neutrinos Phys. Rev. C 70 (2004)
  052501.) (Fedor imkovic, Peter Bene - theory)

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