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• Background Limitation for Simple bolometers• Principles of operation• Cd-Mo based crystals• ZnSe crystals• Conclusions
Stefano Pirro
Ilias 6th Annual Meeting - Dresden 16 - 19 February 2009
JRA2 Highlights JRA2 Highlights –– Scintillating Bolometers Scintillating Bolometers
- Milano
Sum energy: 5407 keV
210Po α
line
3600 keV
Bkg in DBD region
Continuum
2530 keV
CUORICINO TO CUOREA serious problem : Surface contaminationsA serious problem : Surface contaminations
Environmental “underground” Background:238U and 232Th trace contaminations
Surface and Bulk contaminationsSurface and Bulk contaminations
CUORICINO α
Background
130Te76Ge
100Mo116Cd
Furthermore a not negligible part of the background can arise from high energy neutrons from μ-spallation
γ-region α-region
82Se
Principles of operationPrinciples of operation
τ=C/GΔT=ΔE/C
A Bolometric Light Detector is fully active a particle detector
The QE of a BLD is, probably close to 1 but it is rather difficult to measure it
The time response of a BLD is the same of a standard bolometer O (ms)
Light Light DetectorsDetectors -- PerformancesPerformancesOur Light detectors are generally Pure Germanium disks (thickness 0.3-1 mm) . The Performance of a LD are normally evaluated through the Energy resolution on the 55Fe doublet (6 & 6.5 keV X-Ray)
Ge (Ø = 66 mm)
FWHM=550 eV
Ge (Ø = 35 mm)
FWHM=250 eV
Our SetupOur Setup
3x3x3 cm3 CaF2
3x3x6 cm3 CdWO4
3x3x2 cm3 CdWO4
Reflecting foils
Light detectors
Li2
MoO4
ZrO2
Good Scintillation light Poor Scintillation light No Scintillation light
MgMoO4
TeO2
SummarySummary of (of (almostalmost) ) allall the the measuredmeasured crystalscrystals
ZnSe
PbMoO4
SrMoO4
CdMoO4
CdWO4
CaF2
CaMoO4ZnMoO4
ResultsResults on the first on the first arrayarray of CdWOof CdWO44
crystalscrystals
(1)(1)
Reflecting Foil
Coupled with a light detector
In may 2008 we performed the first measurement of an Array of 5 CdWO4 crystal to finallydemonstrate the feasibility of this technique
3x3x6 cm3 (420 g) CdWO4
ResultsResults on the first on the first arrayarray of CdWOof CdWO44
crystalscrystals
(2)(2)
CdWO4 – 3x3x6
4 3x3x3 cm3 (215 g each) CdWO4
1 common LD facing the 4 crystals
ResultsResults on the first on the first arrayarray of CdWOof CdWO44
crystalscrystals
(3)(3)
Internal Roman lead shield
CdWO4 3x3x6 cm3
4 CdWO4 3x3x3 cm3 crystal array
Large light detector
CUORE test crystal
Small light detector
ResultsResults on the first on the first arrayarray of CdWOof CdWO44
crystalscrystals
(4)(4)The data analysis on the 4 3x3x3 cm3 crystals is not finished. The data on the single 3x3x6 cm3 crystal is presented here.The obtained scatter plot is shown it corresponds to 1066 hours of background measurement
Back
groun
d-Free
area
2615 keV 208Tl γ
The MC simulation predicts a background level of 10-4 c/keV/kg/y in the region of interest
44 days background
ResultsResults on on ““largelarge”” crystalscrystals –– CaMoOCaMoO44
CaMoO4 is not a “perfect candidate” for future DBD Experiment since it contains 48Ca
But this compound did show an extreme interesting feature
Decay time of the CaMoO4 crystal – no light detection
CaMoO4 Bolometers permits alpha discrimination without Light detection !!!!
Rise time of the CaMoO4 crystal – no light detection
147Sm- 2310 keV
ZnMoOZnMoO4 4 –– A promising MolibdateA promising Molibdate
A 22 g ZnMoO4 crystal was grown by Institute for Scintillation Materials (Kharkov, Ukraine) In collaboration with by Institute for Nuclear Research (Kiev, Ukraine)
226Ra, 222Rn, 218Po, 214Bi-214Po
(56 mBq/kg)
210Pb
(360 mBq/kg)
ZnSe ZnSe –– an extremely interesting compound (1)an extremely interesting compound (1)
ZnSe crystal was/is an extremely puzzling and interesting material.ZnSe crystal has a huge scintillation output but the emission spectra is close to the absorption spectra (λ≈1 mm)
It normally doped with Te in order to increase the overall light output (we tested UNDOPED crystals)
≈
4 cm dia, 1.7 cm height, 120 g
2 cm dia 3 cm height, 39 g
ZnSe ZnSe –– an extremely interesting compound (2)an extremely interesting compound (2)
In the first run we observed a “very” strange scatter plot
ZnSe ZnSe –– an extremely interesting compound (3)an extremely interesting compound (3)Li
ght S
igna
l [a
u]
Energy [keV]
224Ra α-source
ZnSe
“Matted” – non optical – surface lapped with 3÷20 μm Al2 O3 powder
“near optical” optical – surface
Light detectorLi
ght S
igna
l [a
u]
Energy [keV]
ZnSe ZnSe –– an extremely interesting compound (4)an extremely interesting compound (4)
Energy [keV]
Ligh
t Sig
nal
[au]
Energy [keV]
Ligh
t Sig
nal
[au]
224Ra α-source
ZnSe
“Matted” – non optical – surface lapped with 3÷20 μm Al2 O3 powder
“near optical” optical – surface
Light detector “Penetration”: 6%
ZnSe ZnSe –– an extremely interesting compound (5)an extremely interesting compound (5)
The “penetration” of alpha particles in the “beta” scintillation region seems to depend on the “surface”
In fact we believe it depends on the residual lapping (non scintillating) powder on the crystal surface
XRF Analysis
We have other clear evidence for this explanation, but other tests will be made in order to proof and in order to AVOID this problem
ZnSe ZnSe –– an extremely interesting compound (6)an extremely interesting compound (6)
But the “major” (nice) surprise comes from the time development of the Scintillation Signal
The scintillation signal has a difference in the O(10ms) range. This effect is absolutely unexpected, even at very low temperatures
ZnSe ZnSe –– an extremely interesting compound (7)an extremely interesting compound (7)
Looking at the coincidences between Heat in ZnSe and “Light” in the light detector, threepopulation appears
β/γ
α
Ionizing particles
ZnSe ZnSe –– an extremely interesting compound (8)an extremely interesting compound (8)
Another important feature is the Decay time of thermal signals in ZnSe(No light signal considered)
337 g “new” ZnSe Crystal
SummarySummary
116Cd CdWO482Se ZnSe
100Mo …. ZnMoO4
Reproducibility Radiopurity Availability α/n rejection
β
LY QF(α/β)keV/MeV [%]
CdWO4 34 19ZnSe (Red) 7.4 420
ZnSe (Yellow) 1.6 395ZnMoO4 1.4 16
ConclusionsConclusions
We tested several types of scintillating crystals with interesting ββ
emitters (100Mo,116Cd, 82Se, 48Ca)
Within them CdWO4 gave excellent results
The first measurements of ZnSe are very promising, even if some more tests are needed
Molibdates needs more R&D both for radioactivity and scintillation light
This technique is the only one that can be used for several interesting DBD emitters with excellent energy resolution.
The energy resolution needed to go towards direct hierarchy can be achieved only by bolometers and Semiconductors…
BackupsBackups
Background Suppression : Bulk contaminationsBackground Suppression : Bulk contaminations
Thanks to Bi-Po’s and Beatles internal contaminations do not play a significant role
BI-Po
Bi-Tl“BEATLE”
Does not hold for 234Pa (Q=2195 keV)
Background analisys 3x3x6 crystal (2)
γ- Background - It is rather low
α
Background
Data Analisys- results on the 4 3x3x3 crystals
CaCaFF22
resultsresults
There is a lack of an actual calibration due to the “lightness”
of the compound
JRA2 Highlights – Scintillating Bolometers A serious problem : Surface contaminations Surface and Bulk contaminationsPrinciples of operation Light Detectors - PerformancesOur SetupSummary of (almost) all the measured crystalsResults on the first array of CdWO4 crystals (1)Results on the first array of CdWO4 crystals (2)Results on the first array of CdWO4 crystals (3)Results on the first array of CdWO4 crystals (4)Results on “large” crystals – CaMoO4ZnMoO4 – A promising MolibdateZnSe – an extremely interesting compound (1)ZnSe – an extremely interesting compound (2)ZnSe – an extremely interesting compound (3)ZnSe – an extremely interesting compound (4)ZnSe – an extremely interesting compound (5)ZnSe – an extremely interesting compound (6)ZnSe – an extremely interesting compound (7)ZnSe – an extremely interesting compound (8)Summary ConclusionsBackupsBackground Suppression : Bulk contaminationsBackground analisys 3x3x6 crystal (2)Data Analisys- results on the 4 3x3x3 crystalsCaF2 results