search for double electron capture in 106 cd using hpge detectors and si pixel detectors
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Search for double electron capture in 106Cd using HPGe detectors and Si pixel detectors
Ivan Štekl for TGV collaborationInstitute of Experimental and Applied Physics
Czech Technical University in Prague
TGV experiment – TGV II detector description, results of Phases I and
II
Present status - utilization of Si pixel detectors (MC simulations,
results of background measurements)
Future plans
JINR Dubna, RussiaJINR Dubna, RussiaIEAP CTU in Prague, Czech IEAP CTU in Prague, Czech
RepublicRepublicCSNSM Orsay, FranceCSNSM Orsay, France
Since 2000, focus on 2EC/EC decay of 106Cd
),(22 10646
10648 raysXPdCde e
keVEkeVkeV XECEC 2319:ROI,2778Q /
106Cd
106Ag
106Pd
0+
0+
0+
2+
1133.8
511.9
511.9
622
Q(EC/EC) = 2770 keV 7.2
1.25%
1+
++ +/EC EC/EC
2νEC/EC 2KX Pd (~21 keV) (+ for e.s.) Main background: Cd KX-rays (~23 keV)
+/EC KXPd + 2 511 (+ for e.s.)
2741.04+
0νEC/EC KXPd + LXPd + 2741 (2229 + 512)
2229
2741
++ 4 511 (+ for e.s.)
1557.7
2717.6
3+
1046
1160
0νEC/EC 2KXPd + (1160 + 1046 + 512)
Decay modes + signatures
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 70 %
E-resolution : 3 4 keV @ 60Co
LE-threshold : 5 6 keV
16 samples (~ 50 µm ) of 106Cd (enrich.75%)
13.6 g ~ 5.79 x 1022 atoms of 106Cd
HPGe
HPGe
Cd
Detectors: 32 HPGe Ø 60 mm x 6 mm
Sensitive volume 20.4 cm2 x 6 mm
Weight of cryostat ~2500 g (Al, Cu, …)
Al ~ 1200 g (including holders ~ 360 g)
Cu ~ 1300 g
PASSIVE SHIELDINGPASSIVE SHIELDING (TGV is located in LSM) (TGV is located in LSM)
Copper> 20 cm
Airtight box
Lead> 10 cm
Polyethylene
filled withboron 16
cm
Schedule of TGV II experiment:
(in Laboratoire Souterrain de Modane, France)
Phase I ~ 10 g (12 samples) of 106Cd (75%) T= 8687h (Feb.2005 – Feb.2006)
Phase II ~ 13.6 g (16 samples) of 106Cd (75%) T ~ 12900h (Dec.2007 – July 2009)
Background I no samples (Aug.2009 – Mar.2010)
Background II 16 samples of Cd.-nat (Apr.2009 – …2010)
Phase I final result
%)90(100.3)( 20106/22/1 yCdT ECEC
• acquisition with 10g of 106Cd after 8687 hours: additional analysis (2D, different energy windows)
T1/2 = 1.0 · 1020 y (Suhonen)
T1/2 = 4.4 · 1021 y (Simkovic)
T1/2 = 8.7 · 1020 y (Hirsch)
T1/2 > 3.0 · 1020 y (TGV-2)
4
8
12
16
20
24
28
32
048121620
-line 238 keV
Counts / day /detector4
8
12
16
20
24
28
32
0.00.51.01.52.02.53.03.54.0
-line 352 keV
Counts / day /detector
Comparision of background in Phase I and Phase II
KXPd
KXPd
KXCd
KXCdROI
ROI
%)90(102.4)( 20106/22/1 yCdT ECEC
ROI
ROI
Phase II, 13.6g of 106Cd, T=12900h
How it compares with calculations
> > 4.2 10 4.2 1020 20 p.w.p.w.
approaching
closed
TGV-2 limits on double beta decay of 106Cd
Phase I Phase II
(10g of106Cd,8687h) (13.6g of 106Cd,12900h)
EC/EC T1/2 ≥ …(90%CL) T1/2 ≥ … (90%CL) (0+→0+,g.s.) 3.0 x 1020 yr 4.2 x 1020 yr (0+→2+
1,512) 4.2 x 1019 yr 1.2 x 1020 yr (0+→0+
1,1334) 3.1 x 1019 yr 1.0 x 1020 yr 0 res.(0+→4+,2741) - 1.7 x 1020 yr 0 res.(0+→ 2718) - 1.6 x 1020 yrβ+/EC (0+→0+,g.s.) 5.9 x 1019 yr 1.1 x 1020 yr(0+→2+
1,512) 5.9 x 1019 yr 1.1 x 1020 yr (0+→0+
1,1334) - 1.6 x 1020 yr β+ β+
(0+→0+,g.s.) 6.0 x 1019 yr 1.4 x 1020 yr(0+→2+
1,512) 5.7 x 1019 yr 1.7 x 1020 yr
2β+ β+ (0+→0+,g.s.) - 1.3 x 1020 yr
Advantages:
better efficiency comparing with TGV II (factor 2)
information about energy + position of registered
X-ray
particle recognition (background vs. signal)
much less material needed (lower background)
measurement at room temperature (easy access)
SiSi
Control unit
Cd foil
TGV-III (SPT) ideaThe potential of the TGVThe potential of the TGV II II setup (based on HPGe detectors) setup (based on HPGe detectors) can be can be extended using more enriched material, bigger weight and longerextended using more enriched material, bigger weight and longer acquisition acquisition timetime
Considering to build a new generation of the setup based on Si pixel Considering to build a new generation of the setup based on Si pixel detectors Timepixdetectors Timepix
SPTSPT - Silicon Pixel TelescopeSilicon Pixel Telescope
Timepix detector
• Portable tracking detector• Room temperature &
noiseless operationChipboard + USB readout interface
Vacuum operation, no cooling
USB readout interface (developed in IEAP CTU in Prague), frame-rate up to 5 fps (USB 1.1)
Compact size, Plug&Play, hot swap
Fully USB powered
Integrated source of variable detector bias voltage (5 – 100V)
Pixelman software package + plugin for particle identificationPixelman software package (developed in IEAP CTU in Prague)
Response examples • Particle type identification• Clusters selected according to size, roundness, linearity,...
May 5, 2010 Pavel Cermak
Alphas Electrons Muons
Muons + electrons
214Bi 214Po 210Pb
K1 K2
Single-side-events
Double-side-event
K1
K2
a) Distance face to face in detector pair: 2 mm (detector - source = 1 mm)
b) Detector dimensions: 1.408 cm x 1.408 cm x 2 mmnumber of pixels: 256 x 256 (pixel size: 55 x 55 microns)
detector material: Si backside contact thickness: 1800 angstroms
backside contact material: Aluminum
c) Source foil: 1.2 cm × 1.2 cm × 50 mm
Vertex and physics: Two 21 keV gamma (106Pd X-rays) emitted from single point chosen in bulk of source in full isotropic solid angle
Tagged patterns:Each X-ray is fully detected in the single pixel either:1) single-side events (SSE) – pixels fired in the same detector2) double-side events (DSE) – pixels fired in both detectors3) Total number of good KK-events SSE+DSE
K2K1
SPT MC simulations (1)
Setup with 2 mm thick Si Timepix detector, source distance = 1 mm:Number of good KK-events registered in two pixels: 12.71 %
- double-side events (DSE): 44.11 % - single-side events (SSE): 55.89 %
- single-side events in adjacent pixels: 0.009 %
Number of events with energy deposit in foil: 76.0 %
Setup with 2 mm thick Si Timepix detector, source distance = 1 m:Number of good KK-events registered in two pixels: 16.66 % - double-side events (DSE): 42.32 % - single-side events (SSE): 57.68 % - single-side events in adjacent pixels: 0.16 %
Number of events with energy deposit in foil: 76.2 %
SPT efficiency of registration (compare with 5.5% for TGV-II):
SPT MC simulations (2)
a) MC results: KK events, source-detector distance = 1 mm
D < 2 mm => 34.5% of registered KK eventsD (0.7 – 4) mm => 68% of registered KK eventsMean distance = 3.2 mm
KK events, source-detector distance = 0 mmD < 2 mm => 84.7% of registered KK eventsD < 4 mm => 98.7% of registered KK eventsMean distance = 1.2 mm
b) For background measurement:D (0.7 – 4) mm => 25% of registered bg events
Using distance cut D (0.7-4) mm
Results of MC:
Improving S/B ratio by factor of 2.6
Distance of pixels hit (comparison of MC and meas.)
Bg measurement from LSM:
Intrinsic background
0
5
10
15
20
25
30
35
40
0 200 400 600 800 1000 1200 1400
E, keV
Co
un
ts /
ho
ur
Chipboard with Si detector
Measured by low-background setup in Modane lab
HPGe planar detector, 150cm3, range 20keV – 1.5MeV
Bonding (In+Sn) Readout chip
Empty PCB Si module
228Th < 10-8 < 0.2 263 ± 8 187 ± 11234Th < 10-6 < 0.9 168 ± 11 123 ± 10
40K < 10-7 < 6.2 < 25 117 ± 28
Contributions per unit (comparison of samples and Si module) [mBq/unit]:
Background signal measurement
E1.vs.E2 SSE
Entries 15
20 days of experimental data from LSM, shielded 5cm of Pb, recording 1s
frames
ROI
Energy spectrum (up to 300keV)
Looking for SSE candidates
(2 clusters in the frame)
Only random coincidences, 0
events in the ROI (19-23 keV)
SPT setup proposalEstimation of limit for EC/EC decay of Estimation of limit for EC/EC decay of 106106Cd for 1 pair of Timepix quads:Cd for 1 pair of Timepix quads:
If background = 0 :
T1/2 > (e . t . Nat . ln2) / ln (1-CL) = 1,95 × 1020 years
90% CL ln (1-CL) = 2.3
e ...... full efficiency (for SPT = 8,54 %)
t ...... time of measurement [years], expected 4 years
Nat ... number of 106Cd atoms in foil, 98% of enrichment
Nat = 1.89 × 1021 atoms
To reach limit of 10To reach limit of 102121 years: years:
We would need 5 quad Timepix pairs
Next step – using stack of Timepix detectors
• To build a prototype based on the four-fold Timepix stack
Developed slightly modified boards allowing face-to-face configuration
Further optimization of the chip carrier board (material of PCB, minimizing amount of material close to the chip)
Summary and future plans• Study of 2EC/EC of 106Cd
• TGV-2 setup (based on HPGe detector telescope) has provided result comparable with theoretical predictions – plan new start with more enriched foils (98.4% of 106Cd)
• Developing next generation setup SPT (Silicon Pixel Telescope) based on Si pixel detectors TimePix – measurement and tuning of intrinsic background, a prototype based on the four-fold Timepix stack.
Not tuned for low-bg applications, working on
detection module design optimization, material
selection (teflon PCB, capton).
Studying background signals – Si TimePix detector located in Modane
underground lab, 3 months of data (3 weeks processed).
Dreaming of 5 quad pairs setup running for couple of years to reach region
of 1021 years.
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