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ILIAS ILIAS GENERAL MEETING - 2006 2006 PARALLEL PARALLEL SESSION SESSION ON ON DBD DBD (EXPERIMENTS) (EXPERIMENTS) Specific Specific heat heat measurement measurement of of crystals crystals to to be be used used in in scintillating scintillating bolometers bolometers for for Double Double Beta Beta Decay Decay Marco Barucci - INFN Firenze Outline In view of the realization of a TeO2 scintillating bolometer, measurements of heat capacity have been carried out on two crystals. The TeO2 crystals were grown from pure Pt crucible by Czochralski method, in the Research Institute for Solid State Physics and Optics (Budapest, Hungary). Marco Barucci 2 Outline Preliminary tests showed that intrinsic low temperature scintillation of the TeO2 material is increased in the case of Nb and Mn doping. Marco Barucci 3 Samples The main features of the two samples are: Sample 1 Sample 2 test sample n. 80505 test sample n. 80507 undoped TeO2 mass: 18.687 g Nb doped: TeO2+Nb2O5 (10-4 mol/mol in the melt) dimensions: ~ 3x1x1 cm3 mass: 18.671 g dimensions: ~ 3x1x1 cm3 Marco Barucci 4 Goals Present measurements were aimed to: detecting possible increase of the low temperature specific heat in the case of Nb doping (possible paramagnetic effects at very low temperatures from Nb3+ uneven ions) check the value of specific heat for TeO2 crystals made by different manufacturers. Marco Barucci 5 Experimental Set-Up The measurements were carried out in a low power dilution refrigerator by the thermal relaxation method. R(T) Thermo Heat sink Thermal coupling Heater Power C(T) R(T)=G-1(T) Temp Crystal sample τ(T) Heat capacity C(T) = G(T) x τ(T) time Marco Barucci 6 Experimental Set-Up The sample was sustained by two thin Sn cylinders, which also gave the thermal conductance to the bath Two copper springs ensured the mechanical stability of the sample A Ge thermometer (NTD 35B 3x3x1 mm3) and a Si heater, glued onto the sample, were connected by NbTi wires 25 µm in diameter. Cu springs NbTi wires Sn cylinders (8mmØ (8mmØ, 3mm long, 0,2mm thikness) thikness) NTD Ge thermometer Si heater (other side) TeO2 sample Marco Barucci 7 Experimental Set-Up This configuration allows to minimize the spurious contributions (the addendum) to the heat capacity of the sample. The heat capacity measurements have been carried out from 50 to 130 mK. The range of temperature was limited at the lowest temperature by the small mass of the samples (the thermal discharge time constant became very short) and at the highest temperature by the low sensitivity of the Ge NTD thermometer. Marco Barucci 8 Results specific heat of sample 1 (pure TeO2) sample 2 (Nb doped TeO2) Marco Barucci 9 Results the specific heat of the two measured samples are reported together with data for the TeO2 of Chinese production (at present used for the CUORICINO bolometers) measured by our group a few years ago. M. Barucci,et al., J.Low Temp. Phys., 123,p. 303, 2001. Marco Barucci Within the experimental errors, the specific heat of the three samples in the investigated temperature range is the same 10 Conclusion We cannot exclude spurious contributions to the specific heat at temperature below 50 mK. However, since we do not detect tails of lower temperature contributions in our temperature range, it is unlike that such contributions exist. Thus, we suggest the test of a scintillation bolometer based on the niobium doped tellurium dioxide crystal. Marco Barucci 11