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

Measurement of EC/EC process of 106Cd in the experiment
TGV II
I.Štekl, P.Čermák, P.Beneš
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.Šimkovic
Comenius University, Bratislava
1.
2.
3.
4.
5.
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
TGV I :
48Ca:
open cryostat
~ 1.35 x 1022 atoms (1.08 g)
assembled cryostat, PAs
TGV I
cryostat surrounded by Cu shielding
TGV I results (48Ca)
T12/
 (4.2 13..33 )  1019 y
2
T
2
1/ 2
 (4.2
3.3
1.3
)  10 y
19
21
T10/

1
.
5

10
y (90% CL)
2
Published in Nuclear Physics A700(1-2) (2002) 17-24
TGV II
purpose:
• to improve 48Ca result
obtained by TGV I
• to investigate  processes in
106Cd (to focus on 2EC/EC
channel)
106Cd:
2EC/EC:
2e 
Cd 
106
48
Pd  2 e  ( , X  rays )
106
46
Q EC / EC  2778 keV , ROI : 19 keV  E X  23 keV
48Ca:
2:
48
20
Ca 
Ti  2~e  2 e  ( )
48
22
Q   4272 keV , ROI : 2.7 MeV  Ee  4.2 MeV
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
Double Beta Spectrometers
Calorimetric Semiconductor
multi-detector
Source = detector
High efficiency
Energy resolution
76
Ge
Tracking
Source = detector
Multi-source
Angular info
Precise signature
100
Mo
General view of TGV II setup
Copper
> 20 cm
Airtight
box
Lead
> 10 cm
Polyethylene
filled with
boron 16 cm
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 %
U+Th<0.1 ppb
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 )
TGV II
pedestal
open cryostat
TGV II
assembled cryostat, PAs
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)
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
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
Pulse shape analysis (48Ca)
Current

• based on difference
between interaction
of e- and -rays with
detector crystal
Q1
Q2
e
0
10
20
Time, ns
strob
e
Q (integrated charge)

e
Amplitude (energy)
• 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)
Q
Compton edge
gammas
electrons
E
E-Q spectrum, sources: 207Bi + 60Co
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
Suppression of microphonic noise
ADC2
Y
Low frequency
(microphonic)
12µs
Det
PA
4µs
ADC1
X
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
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)
Background measurement
Sources of natural Cd in the TGV II spectrometer (16 foils; 14.5 gr.;
743+161 hours = 903 hours)
Background measurement
Natural Cd (4 foils of natural Cd)+ all kinds of backgr.suppr. – 3736 hours (February
2005 - July 2005)
Measurement of EC/EC decay
Enriched Cd (12 foils), all kinds of backg. suppr. – 3736 hours (February
2005- July 2005)
KX(Pd) and KX(Cd) in
350
KX(Cd)
300
1
250
210Pb(?)
200
150
100
50
10
15
20
25
30
35
40
45
[keV]
120
110
100
90
80
70
60
50
40
30
20
10
0
106Cd
2
KX(Cd)
10
15
20
25
30
35
40
45
E [keV]
106Cd,
10 g, 3000 h
5
4
Pd
Cd
3
2
1
0
10
15
20
25
E [keV]
19 keV - 22 keV
Enriched Cd (12 foils), all kinds of backg.suppr. – 3736 hours (February
2005 - July 2005)
Natural Cd
Enriched Cd
(3.151 g, 3736 h) (9.948 g, 3736 h)
Signal region (19-22 keV)
Backg. region (16-19 keV)+(28-31 keV)
35 events
35 events
58 events
39 events
total weight of natural Cd foils = 3.151 gramms
(events for natural Cd were recalculated for the weight of enriched Cd)
2EC/EC (g.s. -> g.s.) “signal” on the level 2.5 s
0+
Results
1+
0+ 1138
2+
106
106
Ag
0+
106
Cd
2νEC/EC/1138
T1/2 ≥ 5.3 x 1019 y (90%CL)
512
Pd
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)
Summary:
- TGV II is nice equipment for measurement of special  modes
- it could be first direct measurement of 2EC/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)