double beta decay searches with enriched and scintillating bolometers
DESCRIPTION
- Milano - Bicocca. Double beta decay searches with enriched and scintillating bolometers. Stefano Pirro. The Future of Neutrino Mass Measurements - NuMass 2010 INT Seattle February 8-11, 2010. . . . Background Issues (1). X. X. Internal trace contaminations ( 238 U and 232 Th). - PowerPoint PPT PresentationTRANSCRIPT
Stefano Pirro – NuMass 2010
Stefano Pirro
Double beta decay searches with enriched and scintillating bolometers
- Milano - Bicocca
The Future of Neutrino Mass Measurements - NuMass 2010 INT Seattle February 8-11, 2010
Stefano Pirro – NuMass 2010
Background Issues (1)Background Issues (1)
Stefano Pirro – NuMass 2010
Background Issues (2)Background Issues (2)
Internal trace contaminations (238U and 232Th)
Surrounding trace contaminations (238U and 232Th)
Neutron induced background: direct and through (n,n’)
Surface contaminations
Long living - Emitters 106Ru 106Rh (Q=3.5 MeV) (Fission)
110mAg (Q=2.9 MeV) (fast n activation)
X X
Stefano Pirro – NuMass 2010
Surface and Bulk contaminationsSurface and Bulk contaminations
CUORICINO Background
Furthermore a not negligible part of the background can arise from high energy neutrons from -spallation
-region -region
Environmental “underground” Background:238U and 232Th trace contaminations
130Te76Ge
100Mo116Cd
82Se
136 Xe
Stefano Pirro – NuMass 2010
Some History Some History
The first measurement of light and heat in a bolometer was performed in 1992 by the Milano group
But this technique, using a silicon PD at low temperatures showed several difficulties
Radioactivity induced by the PD itself Cold stage charge preamplifier inside the cryostat Relatively small surface area of the PD
For these reasons the technique was abandoned
In 2004 we started to develop bolometer as LD (as CRESST and Rosebud Experiments)
The activity was then funded by INFN through the BoLux (R&D) Experiment* 2007-2009 and by EC
* Responsible: Stefano Pirro
The CUPIDO R&D* project (INFN) funded for 2010 will go on with R&D on this technique.
Stefano Pirro – NuMass 2010
Principles of operationPrinciples of operation
=C/GT=E/C
Stefano Pirro – NuMass 2010
Light Detectors - PerformancesLight Detectors - PerformancesOur Light detectors are generally Pure Germanium disks (thickness 0.3-1 mm) . The Performances of a LD are normally evaluated through the Energy resolution on the 55Fe doublet (5.9 & 6.5 keV X-Ray)
Ge (Ø = 66 mm)
FWHM=550 eV
Ge (Ø = 35 mm)
FWHM=250 eV
Stefano Pirro – NuMass 2010
Li2MoO4
ZrO2
Good Scintillation light Poor Scintillation light No Scintillation light
MgMoO4
TeO2
Summary of (almost) all the measured Summary of (almost) all the measured crystalscrystals
ZnSe
PbMoO4
SrMoO4
CdMoO4
CdWO4
CaF2
CaMoO4
ZnMoO4
Stefano Pirro – NuMass 2010
UndopedUndoped 4848CaCaFF22
There was a lack of an actual calibration due to the “lightness” of the compound; nevertheless theSignal/noise ratio of the CaF2 was excellent.
Calibration (232Th) on a 3x3x3 cm3 PURE CaF2 crystal
In 2007 we tested a CaF2 crystal. The light output was “rather poor” but definitively enough to discriminate alpha’s
Stefano Pirro – NuMass 2010
Results on the first array of Results on the first array of 116116CdCdWOWO44 crystals crystals (1)(1)
CdWO4 – 3x3x6
4 3x3x3 cm3 (215 g each) CdWO4
1 common LD facing the 4 crystals
Stefano Pirro – NuMass 2010
Results on the first array of Results on the first array of 116116CdCdWOWO44 crystals crystals (2)(2)
The data on the single 420 g 3x3x6 cm3 crystal is presented here.The obtained scatter plot is shown it corresponds to 1066 hours of background measurement
Backg
roun
d-Free
area
2615 keV 208Tl
The MC simulation predicts a background level of 10-4 c/keV/kg/y in the region of interest
44 days background
Stefano Pirro – NuMass 2010
ZnZn100100MoMoOO4 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)
Stefano Pirro – NuMass 2010
Ln (Light)
ZnZn8282SeSe – – an extremely Puzzling an extremely Puzzling compound (1)compound (1)
Looking at the coincidences between Heat in ZnSe and “Light” in the light detector, threepopulation appears
/
Ionizing particles
Stefano Pirro – NuMass 2010Calibration with 232Th and a smeared source
210Po
Beta regionRejection > 99.5 %Smeared so
urce
Lig
htZnZn8282SeSe – – an extremely an extremely promisingpromising compound compound
(2)(2)First Results on a 4 cm 5 cm height 337 g ZnSe Crystal
337 g “new” ZnSe Crystal
/
Stefano Pirro – NuMass 2010
““Beyond” Scintillating Beyond” Scintillating bolometersbolometers
Scintillating bolometers are extremely powerful in order to discriminate background.
Nevertheless, they require a double readout that implies a dedicated technical and construction effort.
This is the “price” one has to pay in order to really “knock down” background.
It would be nice to obtain the same w/o this effort…
Stefano Pirro – NuMass 2010
Decay time of the CaMoO4 crystal – no light detectionRise time of the CaMoO4 crystal – no light detection
[ms]
[au]
Results on “large” crystals – Results on “large” crystals – 4848CaCa100100MoMoOO44
CaMoO4 is not a “perfect candidate” for future DBD Experiment since it contains 48CaBut this compound did show an extreme interesting feature
CaMoO4 Bolometers permits alpha discrimination (99,8%) without Light detection without Light detection
147Sm- 2310 keV
The results are obtained on a ~160 g crystal
Stefano Pirro – NuMass 2010
ZnZn8282SeSe – – an extremely an extremely promisingpromising compound compound (3)(3)
This compound shows another very interesting feature: ’s show different thermal pulse development
/
rejection > 97 % without light detection
Stefano Pirro – NuMass 2010
ZnZn100100MoMoOO4 4 –– A A promising Molibdatepromising Molibdate (2) (2)
Light- Heat scatter plot
No Light information - PSA
This seems a characteristic of Molibdate crystals (also observed on other molibdates)
Stefano Pirro – NuMass 2010
Conclusions - IConclusions - I
We tested several types of scintillating crystals with interesting emitters (100Mo,116Cd, 82Se, 48Ca)
Within them CdWO4 is “ready to use”
The “outsider” ZnSe is now, probably, the best candidate , even if some more tests are needed
Molibdates need 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 (0.3 1 % FWHM)
Particle Identification through Pulse Shape Analysis could result in a new, unexpected, ally
Simulations show that a background level of 10-4 c/keV/kg/y can be “easily” reached without too much “restrictions” on internal radioactivity.
Within few months we plan to test 2 small arrays of CdWO4 and ZnSe crystals ( O(kg) ) in order to completely test the technique (unexpected “surprises” can always happen)
Stefano Pirro – NuMass 2010
Conclusions-2 Conclusions-2
221-02/1 ),()( mMZQGT
Different nuclei HAVE to be investigated by DBD experiments
DBD Detectors with Q >2615 keV can reach background levels 2 orders of magnitude smaller with respect to the others
If we think about possible “ III generation experiments” the key point will be(if we consider solved the background issue….) Energy Resolution ( 1 %)
Scintillating Bolometers are the only detectors that can fulfill all these 3 requirements
130Te76Ge
100Mo116Cd
82Se
136 Xe
Gerda-Majorana
CUORE
EXOSuper-Nemo
SNO+