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- 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).

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Double beta decay searches with enriched and scintillating bolometers

- 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

Stefano Pirro – NuMass 2010


Background issues 1

Background Issues (1)

Stefano Pirro – NuMass 2010


Background issues 2

X

X

Internal trace contaminations (238U and 232Th)

Surrounding trace contaminations (238U and 232Th)

Surface  contaminations

Neutron induced background: direct and through (n,n’)

106Ru 106Rh (Q=3.5 MeV) (Fission)

Long living - Emitters

110mAg (Q=2.9 MeV) (fast n activation)

Background Issues (2)

Stefano Pirro – NuMass 2010


Surface and bulk contaminations

-region

-region

76Ge

116Cd

130Te

100Mo

82Se

136 Xe

CUORICINO  Background

Environmental “underground” Background:

238U and 232Th trace contaminations

Surface and Bulk contaminations

Furthermore a not negligible part of the background can arise from high

energy neutrons from -spallation

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

The CUPIDO R&D* project (INFN) funded for 2010 will go on with R&D on this technique.

* Responsible: Stefano Pirro

Stefano Pirro – NuMass 2010


Principles of operation

=C/G

T=E/C

Principles of operation

Stefano Pirro – NuMass 2010


Light detectors performances

FWHM=550 eV

  • Ge (Ø = 35 mm)

FWHM=250 eV

Light Detectors - Performances

Our 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)

Stefano Pirro – NuMass 2010


Summary of almost all the measured crystals

PbMoO4

ZnSe

ZrO2

MgMoO4

CdMoO4

Li2MoO4

TeO2

SrMoO4

CdWO4

CaF2

CaMoO4

ZnMoO4

Summary of (almost) all the measured crystals

Good Scintillation light

Poor Scintillation light

No Scintillation light

Stefano Pirro – NuMass 2010


Undoped 48 ca f 2
Undoped48CaF2

In 2007 we tested a CaF2 crystal. The light output was “rather poor” but definitively enough to

discriminate alpha’s

Calibration (232Th) on a 3x3x3 cm3 PURE CaF2 crystal

There was a lack of an actual calibration due to the “lightness” of the compound; nevertheless the

Signal/noise ratio of the CaF2 was excellent.

Stefano Pirro – NuMass 2010


Results on the first array of 116 cd wo 4 crystals 1

4 3x3x3 cm3 (215 g each) CdWO4

1 common LD facing the 4 crystals

CdWO4 – 3x3x6

Results on the first array of 116CdWO4 crystals (1)

Stefano Pirro – NuMass 2010


Results on the first array of 116 cd wo 4 crystals 2

Background-Free area

2615 keV 208Tl 

Results on the first array of 116CdWO4 crystals (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

44 days background

The MC simulation predicts a background level of 10-4 c/keV/kg/y in the region of interest

Stefano Pirro – NuMass 2010


Zn 100 mo o 4 a promising molibdate

226Ra, 222Rn, 218Po, 214Bi-214Po

(56 mBq/kg)

210Pb

(360 mBq/kg)

Zn100MoO4 –A 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)

Stefano Pirro – NuMass 2010


Zn 82 se an extremely puzzling compound 1

Ionizing particles

/

Ln (Light)

Zn82Se –an extremely Puzzling compound (1)

Looking at the coincidences between Heat in ZnSe and “Light” in the light detector, three

population appears

Stefano Pirro – NuMass 2010


Zn 82 se an extremely promising compound 2

337 g “new” ZnSe Crystal

/

Betaregion

Calibration with 232Th and a smeared  source

Light

Zn82Se –an extremely promising compound (2)

First Results on a 4 cm  5 cm height 337 g ZnSe Crystal

210Po

Smeared  source

Rejection > 99.5 %

Stefano Pirro – NuMass 2010


Beyond scintillating bolometers

It would be nice to obtain the same w/o this effort…

“Beyond” Scintillating bolometers

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.

Stefano Pirro – NuMass 2010


Results on large crystals 48 ca 100 mo o 4

147Sm- 2310 keV

[ms]

Rise time of the CaMoO4 crystal – no light detection

Decay time of the CaMoO4 crystal – no light detection

[au]

Results on “large” crystals – 48Ca100MoO4

CaMoO4 is not a “perfect candidate” for future DBD Experiment since it contains 48Ca

But this compound did show an extreme interesting feature

The results are obtained on a ~160 g crystal

CaMoO4 Bolometers permits alpha discrimination (99,8%) without Light detection

Stefano Pirro – NuMass 2010


Zn 82 se an extremely promising compound 3

/

Zn82Se –an extremely promising compound (3)

This compound shows another very interesting feature: ’s show different thermal pulse development

rejection > 97 % without light detection

Stefano Pirro – NuMass 2010


Zn 100 mo o 4 a promising molibdate 2

No Light information - PSA

This seems a characteristic of Molibdate crystals (also observed on other molibdates)

Zn100MoO4 –A promising Molibdate (2)

Light- Heat scatter plot

Stefano Pirro – NuMass 2010


Conclusions i
Conclusions - 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)

  • 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)

  • Particle Identification through Pulse Shape Analysis could result in a new, unexpected, ally

Stefano Pirro – NuMass 2010


Conclusions 2

CUORE

76Ge

116Cd

130Te

100Mo

82Se

Gerda-Majorana

136 Xe

SNO+

EXO

Super-Nemo

Conclusions-2

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

Stefano Pirro – NuMass 2010


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