• 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