Stefano Pirro. JRA2 Highlights Scintillating Bolometers. -Milano

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1 JRA2 Highlights Scintillating Bolometers Stefano Pirro -Milano Background Limitation for Simple bolometers Principles of operation Cd-Mo based crystals ZnSe crystals Conclusions Ilias 6 th Annual Meeting - Dresden February 2009

2 A serious CUORICINO problem : Surface TO CUORE contaminations Bkg in DBD 210 Po α line region Continuum Sum energy: kev

3 Surface and Bulk contaminations γ-region α-region 76 Ge 130 Te 116 Cd 100 Mo 82 Se CUORICINO α Background Environmental underground Background: 238 U and 232 Th trace contaminations Furthermore a not negligible part of the background can arise from high energy neutrons from μ-spallation

4 Principles of operation τ=c/g ΔT=ΔE/C A Bolometric Light Detector is fully active a particle detector The time response of a BLD is the same of a standard bolometer O (ms) The QE of a BLD is, probably close to 1 but it is rather difficult to measure it

5 Light Detectors - Performances Our Light detectors are generally Pure Germanium disks (thickness mm). The Performance of a LD are normally evaluated through the Energy resolution on the 55 Fe doublet (6 & 6.5 kev X-Ray) Ge (Ø = 66 mm) FWHM=550 ev Ge (Ø = 35 mm) FWHM=250 ev

6 Our Setup 3x3x2 cm 3 CdWO 4 3x3x6 cm 3 CdWO 4 3x3x3 cm 3 CaF 2 Light detectors Reflecting foils

7 Summary of (almost( almost) all the measured crystals Good Scintillation light Poor Scintillation light No Scintillation light PbMoO 4 ZnSe CdMoO 4 ZrO 2 Li 2 MoO 4 MgMoO 4 TeO 2 SrMoO 4 CdWO 4 CaF 2 CaMoO 4 ZnMoO 4

8 Results on the first array of CdWO 4 crystals (1) In may 2008 we performed the first measurement of an Array of 5 CdWO 4 crystal to finally demonstrate the feasibility of this technique Coupled with a light detector Reflecting Foil 3x3x6 cm 3 (420 g) CdWO 4

9 Results on the first array of CdWO 4 crystals (2) 4 3x3x3 cm 3 (215 g each) CdWO 4 1 common LD facing the 4 crystals CdWO 4 3x3x6

10 Results on the first array of CdWO 4 crystals (3) CUORE test crystal Large light detector 4 CdWO 4 3x3x3 cm 3 crystal array CdWO 4 3x3x6 cm3 Small light detector Internal Roman lead shield

11 Results on the first array of CdWO 4 crystals (4) The data analysis on the 4 3x3x3 cm 3 crystals is not finished. The data on the single 3x3x6 cm 3 crystal is presented here. The obtained scatter plot is shown it corresponds to 1066 hours of background measurement 2615 kev 208 Tl γ Background-Free area 44 days background The MC simulation predicts a background level of 10-4 c/kev/kg/y in the region of interest

12 Results on large crystals CaMoO 4 CaMoO 4 is not a perfect candidate for future DBD Experiment since it contains 48 Ca But this compound did show an extreme interesting feature 147 Sm kev Decay Rise time time of of the the CaMoO CaMoO 4 crystal 4 crystal no no light light detection detection CaMoO 4 Bolometers permits alpha discrimination without Light detection!!!!

13 ZnMoO 4 A promising Molibdate A 22 g ZnMoO 4 crystal was grown by Institute for Scintillation Materials (Kharkov, Ukraine) In collaboration with by Institute for Nuclear Research (Kiev, Ukraine) 226 Ra, 222 Rn, 218 Po, 214 Bi- 214 Po (56 mbq/kg) 210 Pb (360 mbq/kg)

14 ZnSe 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

15 ZnSe an extremely interesting compound (2) In the first run we observed a very strange scatter plot

16 ZnSe an extremely interesting compound (3) Light Signal [au] Light Signal [au] Energy [kev] Energy [kev] Light detector ZnSe near optical optical surface 224 Ra α-source Matted non optical surface lapped with 3 20 μm Al 2 O 3 powder

17 ZnSe an extremely interesting compound (4) Light Signal [au] Light Signal [au] Energy [kev] Energy [kev] Light detector Penetration : 6% <1 % ZnSe Matted non optical surface lapped with 3 20 μm Al 2 O 3 powder 224 Ra α-source near optical optical surface

18 ZnSe an extremely interesting compound (5) XRF Analysis 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 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

19 ZnSe 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

20 ZnSe an extremely interesting compound (7) α β/γ Ionizing particles Looking at the coincidences between Heat in ZnSe and Light in the light detector, three population appears

21 ZnSe 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

22 Summary Reproducibility Availability Radiopurity α/n rejection 116 Cd CdWO 4 82 Se ZnSe 100 Mo. ZnMoO 4 β LY QF(α/β) kev/mev [%] CdWO ZnSe (Red) ZnSe (Yellow) ZnMoO

23 Conclusions We tested several types of scintillating crystals with interesting ββ emitters ( 100 Mo, 116 Cd, 82 Se, 48 Ca) Within them CdWO 4 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

24 Backups

25 Background Suppression : Bulk contaminations BI-Po BEATLE Bi-Tl Thanks to Bi-Po s and Beatles internal contaminations do not play a significant role Does not hold for 234 Pa (Q=2195 kev)

26 Background analisys 3x3x6 crystal (2) α Background γ- Background - It is rather low

27 Data Analisys- results on the 4 3x3x3 crystals

28 CaF 2 results There is a lack of an actual calibration due to the lightness of the compound