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First results of double beta decay experiment
with 106CdWO4 crystal scintillator
P. Belli1, R. Bernabei1,2, R. S. Boiko3, V. B. Brudanin4, F. Cappella5,6,
V. Caracciolo7, R. Cerulli7, D. M. Chernyak3, F. A. Danevich3, S. d'Angelo1,2,
A. E. Dossovitskiy8, E. N. Galashov9, A. Incicchitti5,6, V. V. Kobychev3,
S. S. Nagorny3, F. Nozzoli1, B. N. Kropivyansky3, V. M. Kudovbenko3,
A. L. Mikhlin8, A. S. Nikolaiko3, D. V. Poda3,7, R. B. Podviyanuk3,
O. G. Polischuk3, D. Prosperi5,6, V. N. Shlegel9, Yu. G. Stenin9, J. Suhonen10,
V. I. Tretyak3, Ya. V. Vasiliev9
1
INFN sez. Roma Tor Vergata, Rome, Italy
2 Dip. di Fisica, Università di Roma ”Tor Vergata”, Rome, Italy
3 Institute for Nuclear Research, Kyiv, Ukraine
4 Joint Institute for Nuclear Research, Dubna, Russia
5 INFN, sez. Roma, Rome, Italy
6 Dipartimento di Fisica, Università di Roma La Sapienza, Rome, Italy
7 INFN, Laboratori Nazionali del Gran Sasso, Assergi (AQ), Italy
8 Joint Stock Company NeoChem, Moscow, Russia
9 Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia
10 Department of Physics, University of Jyväskylä, Jyväskylä, Finland
1
Double beta decay of 106Cd
106Cd
natural
abundance
is 1.25(6)%
2
Development of 106CdWO4 scintillator [1]
•
•
•
•
•
Enriched 106Cd – 66%
Crystal growth: Low-thermal-gradient Czochralski technique
Mass of 106CdWO4 charge – 265 g
Mass of single crystal boule – 231 g (87.2%)
Non-recoverable losses – 0.78 g (0.3%)
Boule 106CdWO4
(231 g)
Scintillator 106CdWO4
≈∅27×50 mm (215.4 g)
3
[1] P. Belli et al., NIMA 615 (2010) 301
3
Detector with 106CdWO4
DAMA R&D set-up at LNGS (Italy)
Size, mm
Mass, g
Live time, h
∅27×50
215.4
3929 (1320 with Eγ > 1.8 MeV)
Polystyrene Light-guide
3’’ PMT EMI9265
106CdWO
4
Quartz Light-guide
4
DAMA R&D set-up [1]
Laboratori Nazionali del Gran Sasso
Copper
Detector
Paraffin
Lead
Hermetic
Plexiglass
box
Cadmium
5
[1] R. Bernabei et al., Nuovo Cim. A 112 (1999) 545
Calibration by γ quanta
Calibration sources: 22Na, 60Co, 131Ba, 137Cs, and 228Th
ZnWO4 ∅41×27 mm, 239 g
FWHMγ=(11.2 Eγ)1/2
6
Background spectrum of 106CdWO4
106CdWO
4
1320 h
7
Pulse-shape discrimination with 106CdWO4
106CdWO
4
∅27×50 mm, 216 g, 2400 h
Overlapped
pulses
Overlapped pulses
Overlapped
pulses
8
Pulse-shape discrimination with 106CdWO4
106CdWO
4
1320 h
9
Time-amplitude
analysis
106CdWO
4
4183 h
220Rn
↓α
216Po (T = 145 ms)
1/2
↓α
212Bi
10
Radioactive contaminations of the 106CdWO4 crystal
Source
Activity, mBq/kg
116CdWO
4
CdWO4
106CdWO
215 g
0.053(9) b
0.039(2) c
≤ 0.026 b
≤ 0.014 c
≤ 0.1 b
0.053(5) c
≤ 0.6 b
≤ 0.5 b
≤ 0.004 b
≤ 0.045 b
≤ 0.18 b
≤ 0.018 b
≤ 0.063 b
≤ 0.3 b
≤ 0.8 b
≤ 0.3 b
≤ 0.3 b
Σα
1.40(10) b
0.26(4) b
2.1(1) b
40K
0.3(1) a
91(5) a
0.43(6) a
≤5a
558(4) a
≤ 3.4 a
≤ 11 a
174
112(5) Bq/kg a
1.3(3) a
232Th
228Th
238U
+ 234U
230Th
226Ra
210Po
113Cd
113mCd
207Bi
a
– Fit of background spectra.
b – Pulse shape discrimination.
c – Time-amplitude analysis.
11
Simulated response functions to 2β
processes in 106CdWO4 scintillator
12
Resonant double electron capture of 106Cd
Resonant LK capture?
Resonant 2K capture?
2742(7)
2721(7)
13
Resonant enhancement
of 0ν2ε capture in 106Cd
T1/ 2 (yr) = 5.561× 10
23
x + 9.42 eV
2
mν
2
2
14
Half-life limits on 2β processes in 106Cd
Decay channel
Level of 106Pd
Experimental limit on T1/2 at 90% C.L.
Present work
Best previous limits
0ν2ε
g.s.
≥ 3.6 × 1020
≥ 8.0 × 1018
2νεβ+
g.s.
≥ 7.2 × 1019
≥ 4.1 × 1020
2+1 512 keV
≥ 9.0 × 1019
≥ 2.6 × 1020
2+1 1128 keV
≥ 3.2 × 1020
≥ 1.4 × 1020
0+1 1134 keV
≥ 3.5 × 1020
≥ 1.6 × 1020
0νεβ+
g.s.
≥ 2.1×1020
≥ 3.7 × 1020
2ν2β+
g.s.
≥ 2.5 × 1020
≥ 2.4 × 1020
2+1 512 keV
≥ 3.2 × 1020
≥ 1.7 × 1020
0ν2β+
g.s.
≥ 2.1 × 1020
≥ 2.4 × 1020
Resonant 0ν2K
2718 keV
≥ 1.4 × 1020
≥ 1.7 × 1020 [*]
Resonant 0νKL
2741 keV
≥ 3.2 × 1020
≥ 1.6 × 1020
15
Conclusions and perspectives
• An experiment using a cadmium tungstate crystal scintillator
enriched in 106Cd up to 66% is in progress in the DAMA R&D
set-up at the Laboratori Nazionali del Gran Sasso of INFN.
• The total α activity of the 106CdWO4 scintillator is on the level of
≈ 2 mBq/kg. The main components of background of the
detector are β active 113mCd (112 Bq/kg) and 207Bi (1.3 mBq/kg).
• Lower limits on half-lives for 2β processes in 106Cd were set on
the level of 1020 yr.
• A possible resonant enhancement of 0ν2ε processes was
estimated in the framework of QRPA approach.
• A sensitivity of the experiment to different 2β processes in
106Cd after ≈ 3 yr of measurements is expected to be on the
16
level of ~ 1021 yr.