Search

The Boltzmann constant k has been determined from a measurement of the speed of sound in helium gas in a quasi-spherical resonator (volume 0.5 l) maintained at a temperature close to the triple point of water (273.16 K). The acoustic velocity c is deduced from measured acoustic resonance frequencies and the dimensions of the quasi-sphere, the latter being obtained via simultaneous microwave resonance. Values of c are extrapolated to the zero pressure limit of ideal gas behaviour. We find J⋅K−1, a result consistent with previous measurements in our group and elsewhere. The value for k, which has a relative standard uncertainty of 1.02 ppm, lies 0.02 ppm below that of the CODATA 2010 adjustment.

International audience; The International Committee for Weights and Measures (CIPM), at its meeting in October 2017, followed the recommendation of the Consultative Committee for Units (CCU) on the redefinition of the kilogram, ampere, kelvin and mole. For the redefinition of the kelvin, the Boltzmann constant will be fixed with the numerical value 1.380 649 × 10−23 J K−1. The relative standard uncertainty to be transferred to the thermodynamic temperature value of the triple point of water will be 3.7 × 10−7, corresponding to an uncertainty in temperature of 0.10 mK, sufficiently low for all practical purposes. With the redefinition of the kelvin, the broad research activities of the temperature community on the determination of the Boltzmann constant have been very successfully completed. In the following, a review of the determinations of the Boltzmann constant k, important for the new definition of the kelvin and performed in the last decade, is given.

The SI unit of temperature will soon be redefined in terms of a fixed value of the Boltzmann constant k derived from an ensemble of measurements worldwide. We report on a new determination of k using acoustic thermometry of helium-4 gas in a 3-litre volume quasi-spherical resonator. The method is based on the accurate determine of acoustic and microwave resonances to measure the speed of sound at different pressures. We find for the universal gas constant R = 8.31 44614 (50) Jmol-1K-1. Using the current best available value of the Avogadro constant, we obtain k = 1.38 064 878(83) ×10^(23) JK-1 with u(k) / k = 0.60 x 10^(-6), where the uncertainty u is one standard uncertainty corresponding to a 68 % confidence level. This value is consistent with previous determinations and with that of the 2014 CODATA adjustment of the fundamental constants (Mohr et al., Rev. Mod. Phys. 88, 035009 (2016)), within the standard uncertainties. We combined the present values of k and u(k) with earlier values that were measured at LNE. Assuming the maximum possible correlations between the measurements, (klsubgpresentl/subg/〈k〉-1) = 0.071×10lsupg-6l/supg and the combined ur(k) is reduced to 0.56×10lsupg-6l/supg. Assuming minimum correlations, (klsubgpresentl/subg/〈k〉-1) = 0.10×10lsupg-6l/supg and the combined ur(k) is reduced to 0.49×10lsupg-6l/supg.

Previous research effort towards the determination of the Boltzmann constant has significantly improved the supporting theory and the experimental practice of several primary thermometry methods based on the measurement of a thermodynamic property of a macroscopic system at the temperature of the triple point of water. Presently, experiments are under way to demonstrate their accuracy in the determination of the thermodynamic temperature T over an extended range spanning the interval between a few kelvin and the copper freezing point (1358 K). We discuss how these activities will improve the link between thermodynamic temperature and the temperature as measured using the International Temperature Scale of 1990 (ITS-90) and report some preliminary results obtained by dielectric constant gas thermometry and acoustic gas thermometry. We also provide information on the status of other primary methods, such as Doppler broadening thermometry, Johnson noise thermometry and refractive index gas thermometry. Finally, we briefly consider the implications of these advancements for the dissemination of calibrated temperature standards.

The paper reports a new experiment to determine the value of the Boltzmann constant, , with a relative standard uncertainty of 1.2 parts in 10 6 . k B was deduced from measurements of the velocity of sound in argon, inside a closed quasi-spherical cavity at a temperature of the triple point of water. The shape of the cavity was achieved using an extremely accurate diamond turning process. The traceability of temperature measurements was ensured at the highest level of accuracy. The volume of the resonator was calculated from measurements of the resonance frequencies of microwave modes. The molar mass of the gas was determined by chemical and isotopic composition measurements with a mass spectrometer. Within combined uncertainties, our new value of k B is consistent with the 2006 Committee on Data for Science and Technology (CODATA) value: ( k new B / k B_CODATA −1)=−1.96×10 −6 , where the relative uncertainties are and u r ( k B_CODATA )=1.7×10 −6 . The new relative uncertainty approaches the target value of 1×10 −6 set by the Consultative Committee on Thermometry as a precondition for redefining the unit of the thermodynamic temperature, the kelvin.

In the temperature range between 0.65 K and 5 K, the International Temperature Scale of 1990 (ITS-90) is based on 3He and 4He vapor-pressure thermometers. Between 0.65 K and 1 K, the ITS-90 overlaps with the Provisional Low Temperature Scale of 2000 (PLTS-2000), defined in term of the melting pressure of 3He. Some differences, up to more than 1 mK, exist between the two scales in the overlapping interval. The LNE-CNAM has recently started the construction of a 3He–4He vapor-pressure thermometer to realize the ITS-90 in its lowest subrange at the highest degree of accuracy. The device is provided with two separate vapor-pressure chambers, one for 3He and the other for 4He, built in a single copper block, and is installed in the experimental space of a dilution refrigerator. The vapor-pressure thermometer is designed to accommodate on the same copper block several transfer standards, an acoustic thermometer, and the 3He melting-pressure thermometer. This configuration is intended for realizing calibrations of transfer standards down to 0.65 K, for investigating the possibility to extend the acoustic thermometer below 4 K, and to perform a direct comparison between the ITS-90 and the PLTS-2000 in the overlapping temperature range, in order to study their differences. The realization of the system has been recently accomplished, and this report illustrates the characteristics of such an experimental device.

Pitch-bonded graphites are among the best known thermal insulators at sub-kelvin temperatures, but are very good conductors at higher temperatures. This makes them ideal for mechanical supports which must provide good thermal isolation at an operating temperature below 1 K, but must have good conductance at higher temperatures to aid in initially cooling down an instrument (a “passive heat switch”). One type of graphite, AGOT, has been known as having the lowest thermal conductivity below 1 K not only among graphites, but also compared with any other material. It is, however, no longer available. We have carried out thermal conductivity measurements at temperatures between 60 mK and 4 K on a proposed replacement, POCO AXM-5Q graphite, as well as a sample of AGOT graphite. Our measurements show that both graphites have a difference of about six orders of magnitude in conductivity between room temperature and 100 mK, but that AGOT graphite is not as good an insulator as previously believed. We conclude that AXM-5Q graphite is not only a suitable replacement for AGOT, but in fact is somewhat superior.

In this paper we report about the properties of Neutron Transmutation Doped (NTD) Ge in magnetic fields, focusing on the electrical conduction properties and magnetoresistance, in view of a use as sensors for bolometers in magnetic field. Samples of two different doping density were studied in magnetic field up to 5 T and temperature down to 65 mK. NTD sensors show a reproducible gigantic magnetoresistance that leads to an enhancement of their sensitivity to temperature variations. We discuss preliminarily the possible use of NTD sensors in magnetic field in particle detector developments, in particular for the KATRIN experiment.

At very low temperatures, the tunnelling theory for amorphous solids predicts a thermal conductivity κ α Tm, with m = 2. However, most of the data in the literature in the temperature range 0.1–1 K report an m

The specific heat of Torlon has been measured in the 0.15–4.2 K temperature range. Data below 1 K can be represented by c ( T ) = P 1 T 1+ δ + P 2 T 3 , with P 1 = (5.41 ± 0.08)·10 −6 J K −(2+ δ ) g −1 , P 2 = (2.82 ± 0.03) ·10 −5 JK −4 g −1 and δ = 0.28 ± 0.01, as predicted by the tunnelling theory. Above 1 K, the behaviour of c ( T ) is similar to that of other amorphous materials and can be expressed as: c ( T ) = P · T Ω with P = (2.68 ± 0.07)·10 −5 JK Ω +1 g −1 and Ω = 3.32 ± 0.02.

Neutron Transmutation Doped (NTD) germanium thermistors, cut from metallized wafers, are useful in bolometry. The rise time of a bolometer depends on its heat capacity. We report measurements on the heat capacity of two NTD Ge wafers down to 24 mK temperatures. Both wafers were neutron irradiated and annealed, one of them had in addition undergone a boron implantation and metallization process. For the non-metallized wafer we found a Sommerfeld constant γ = 7.52·10−7 J K−2 cm−3. A comparison between the two wafers showed an excess heat capacity in the metallized wafer. For example, at 24 mK temperature, the specific heat of the metallized afer is more than twice the value of the non-metallized one.

We report about the measurement of the electric characteristics of some NTD Ge thermistors at temperatures down to 25 mK. The dopant concentration is around 6 × 10 16 cm - 3 , producing a material of characteristics close to the metal-to-insulator transition. Fitting the ρ ( T ) characteristics with a variable exponent p Mott's law, a p around 0.6 was obtained. This result confirms the hypothesis of a dependence of p on the doping level.

Torlon is an organic polymer (polyamide-imide) which exhibits room temperature good mechanical and thermal properties and high chemical resistance. The thermal conductivity of Torlon 4203 was measured in the range of temperature 4.2–300 K. These data complete existing measurement in the temperature range 0.1–5 K. The thermal conductivity shows a linear behavior between 30 K and 250 K and a plateau, typical of many amorphous materials, around 7 K.

We report data of thermal conductivity between 30 and 150 mK of three different types of commercial copper, before and after a thermal treatment of the samples. The measurements show that both purity and thermal treatment strongly influence the value of thermal conductivity. Data show a strict linear dependence on the temperature of the thermal conductivity.

The CUORICINO ββ-decay detector is an array of 62 TeO2 bolometers; 44 are 5×5×5-cm crystals made with natural tellurium (33.8% 130Te). There are 18, 3×3×6-cm crystals, 14 of which are made of natural tellurium, 2 are isotopically enriched to 75% in 130Te, and 2 are enriched to 82.3% in 128Te. The total mass of 130Te is ∼ 11 kg. The background rate is 0.23 ± 0.04 counts/keV/kg/yr in the energy interval 2480 to 2600 keV. During the cooling process, some of the wires became disconnected and only 32 of the large and 16 of the smaller crystals could be read out. The data presented here come from 29 of the 5×5×5-cm crystals containing 6.2 kg of 130Te. The new limit on the half-life is \(T_{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}}^{0\nu } \geqslant 5 \times 10^{23} yr\), corresponding to an effective Majorana mass of the electron neutrino 〈mν〉 between 0.42 and 2.05 eV, depending on the nuclear model used to analyze the data.

The first results are reported on the limit for neutrinoless double decay of 130Te obtained with the new bolometric experiment CUORICINO. The set-up consists of 44 cubic crystals of natural TeO2, 5 cm on the side and 18 crystals of 3×3×6 cm3. Four of these latter crystals are made with isotopically enriched materials: two in 128Te and two others in 130Te. With a sensitive mass of ∼40 kg, our array is by far the most massive running cryogenic detector to search for rare events. The array is operated at a temperature of ∼10 mK in a dilution refrigerator under a heavy shield in the Gran Sasso Underground Laboratory at a depth of about 3500 m.w.e. The counting rate in the region of neutrinoless double beta decay is ∼0.2 counts keV−1kg−1y−1, among the lowest in this type of experiment. No evidence for neutrinoless double beta decay is found with the present statistics obtained in about three months with a live time of 72%. The corresponding lower limit for the lifetime of this process is of 5.5×1023 years at 90% C.L. The corresponding limit for the effective neutrino mass ranges between 0.37 to 1.9 eV depending on the theoretically calculated nuclear matrix elements used. This constraint is the most restrictive one except those obtained with Ge diodes, and is comparable to them.

Purpose of this experiment was to select the best material for the construction of thermal links aiming at cooling down sensitive masses of the order of 100–1000 kg for the detection of rare decays and gravitational waves. We report on the technique used to measure the thermal conductivity at very low temperatures (down to 30 mK) of three different types of copper, before and after a thermal treatment of the samples. The most conductive copper was used for the thermal link of the CUORICINO experiment, where a mass of about 60 kg needs to be cooled down to a few mK. The cool down time was reduced by at least one order of magnitude with respect to previous similar experiments. An important contribution to this successful result came also from an improved procedure for controlling the residual heating provided by the conversion from ortho- to para-hydrogen in copper.

We have studied the low temperature thermal properties of a polypropylene copolymer (PP): thermal conductivity (between 0.1 and 4 K), specific heat (between 0.06 and 1 K) and thermal expansion (from 4.2 K to room temperature). Both the thermal conductivity and the specific heat temperature data were interpreted using the tunnelling model for phonon scattering. The measured thermal properties show that PP is suitable for use as thermal insulating support material in cryogenic devices.

At the end of 2001 the Milano Double Beta Decay (MI-DBD) experiment on double beta decay of 130Te has been completed. The project Cryogenic Underground Observatory for Rare Events (CUORE), proposed as a natural extension of MI-DBD, will be a tightly packed array of 1000 TeO2 bolometers, each being a cube 5 cm on a side with a mass of 790 g. The array will consists of 25 vertical towers, arranged in a square of 5 towers by 5 towers, each containing 10 layers of 4 crystals. A single CUORE tower has been constructed as a smaller scale experiment called CUORICINO. The technical feasibility of CUORE is now being tested in CUORICINO, running since few weeks. The CUORICINO experiment consists of 44 TeO2 detectors 5×5×5 cm3 and 18 TeO2 detectors 3×3×6 cm3 for a total mass of approximately 41 kg. An analysis of the detector performances is presented together with the new limit obtained on neutrinoless double beta decay of 130Te.

Author(s): Andreotti, E; Arnaboldi, C; Avignone, FT; Balata, M; Bandac, I; Barucci, M; Beeman, JW; Bellini, F; Brofferio, C; Bryant, A; Bucci, C; Canonica, L; Capelli, S; Carbone, L; Carrettoni, M; Clemenza, M; Cremonesi, O; Creswick, RJ; Di Domizio, S; Dolinski, MJ; Ejzak, L; Faccini, R; Farach, HA; Ferri, E; Fiorini, E; Foggetta, L; Giachero, A; Gironi, L; Giuliani, A; Gorla, P; Guardincerri, E; Gutierrez, TD; Haller, EE; Kazkaz, K; Kogler, L; Kraft, S; Maiano, C; Martinez, C; Martinez, M; Maruyama, RH; Newman, S; Nisi, S; Nones, C; Norman, EB; Nucciotti, A; Orio, F; Pallavicini, M; Palmieri, V; Pattavina, L; Pavan, M; Pedretti, M; Pessina, G; Pirro, S; Previtali, E; Risegari, L; Rosenfeld, C; Rusconi, C; Salvioni, C; Sangiorgio, S; Schaeffer, D; Scielzo, ND; Sisti, M; Smith, AR; Tomei, C; Ventura, G; Vignati, M | Abstract: The CUORICINO experiment was an array of 62 TeO2 single-crystal bolometers with a total 130Te mass of 11.3kg. The experiment finished in 2008 after more than 3 yr of active operating time. Searches for both 0ν and 2ν double-β decay to the first excited 0+ state in 130Xe were performed by studying different coincidence scenarios. The analysis was based on data representing a total exposure of N(130Te)•t=9.5×1025yr. No evidence for a signal was found. The resulting lower limits on the half-lives are T122ν(130Te→130Xe*)g1. 3×1023yr (90% C.L.), and T120ν(130Te →130Xe*)g9.4×1023yr (90% CL). ©2012 American Physical Society.

We present a search for β+/EC double beta decay of 120Te performed with the CUORICINO experiment, an array of TeO2 cryogenic bolometers. After collecting 0.0573 kg · y of 120Te, we see no evidence of a signal and therefore set the following limits on the half-life: T1/20ν>1.9·1021 y at 90% C.L. for the 0ν mode and T1/22ν>7.6·1019 y at 90% C.L. for the 2ν mode. These results improve the existing limits by almost three orders of magnitude (four in the case of 0ν mode). © 2011 Published by Elsevier B.V.

The transition temperature from normal to superconducting state and the specific heat of Al 5056 aluminium alloy in the 0.1 – 3.6 K temperature range have been measured. This alloy is largely used in resonant detectors of gravitational waves. A comparison with specific heat data of the same material obtained by different measuring methods is given.

To better understand the contribution of cosmic ray muons to the CUORICINO background, 10 plastic scintillator detectors were installed at the CUORICINO site and operated during the final 3 months of the experiment. From these measurements, an upper limit of 0.0021 counts/(keV kg yr) (95% CL) was obtained on the cosmic ray-induced background in the neutrinoless double beta decay region of interest. The measurements were also compared to Geant4 simulations., 16 pages, 7 figures

A detailed description of the CUORICINO {sup 130}Te neutrinoless double-beta (0 {nu}{beta}{beta}) decay experiment is given and recent results are reported. CUORICINO is an array of 62 tellurium oxide (TeO{sub 2}) bolometers with an active mass of 40.7 kg. It is cooled to {approx}8-10 mK by a dilution refrigerator shielded from environmental radioactivity and energetic neutrons. It is running in the Laboratori Nazionali del Gran Sasso (LNGS) in Assergi, Italy. These data represent an exposure of 11.83 kg yr or 91 mole-years of {sup 130}Te. No evidence for 0 {nu}{beta}{beta}-decay was observed and a limit of T{sub 1/2}{sup 0} {sup {nu}}({sup 130}Te){>=}3.0x10{sup 24} y (90% CL) is set. This corresponds to an upper limit on the effective mass, , between 0.19 and 0.68 eV when analyzed with the many published nuclear structure calculations. In the context of these nuclear models, the values fall within the range corresponding to the claim of evidence of 0 {nu}{beta}{beta}-decay by H. V. Klapdor-Kleingrothaus et al. The experiment continues to acquire data.

The CUORE detector will be made of 988 TeO2 crystals and will need a base temperature lower than 10 mK in order to meet the performance specifications. To cool the CUORE detector a large cryogen-free cryostat with five pulse tubes and one specially designed high-power dilution refrigerator has been designed. The detector assembly has a total mass of about 1.5 ton and uses a vibration decoupling suspension system. Because of the stringent requirements regarding radioactivity, about 12 tons of lead shielding need to be cooled to 4 K and below, and only a limited number of construction materials are acceptable. The eight retractable radioactive sources for detector calibration and about 2600 signal wires add further complexity to the system. The many stringent and contrasting requirements together with the overall large size made the design of the CUORE cryogenic system a real mechanical and cryogenic engineering challenge. The cryogenic system is expected to be fully operational in the Gran Sasso Laboratory in July 2013. We report here about the current status of the cryogenic system construction, which has started about one year.

The main purpose of the Cryogenic Underground Observatory for Rare Events (CUORE) experiment is the search for the Neutrinoless Double Beta Decay (0νDBD) of 130 Te reaching a sensitivity on Majorana mass better than 50 meV. Cuoricino represents not only the first stage of CUORE, but also the most massive 0νDBD experiment presently running. Present results and future planning of these experiments will be described in the paper.

The CUORE cryogenic system consists of a large cryogen-free cryostat cooled by five pulse tubes and one high-power specially designed dilution refrigerator. About 5 × 10 3 kg of lead shielding are to be cooled to below 1 K and a mass of 1.5 × 10 3 kg must be cooled to 10 mK. Several tie-rods are used to support the different parts of the experiment. We have measured the thermal conductivity below 4 K of two candidate materials for the CUORE suspensions: the Ti6Al4V alloy ( k ( T ) = 0.075 · T exp - 1.636 4.38 K T [ W / m K ] ) and the 316LN stainless steel ( k ( T ) = 0.0556 · T 1.15 [ W / m K ] ) .

We report the present results of the CUORICINO experiment, a cryogenic experiment on neutrinoless Double Beta Decay (DBD) of 130Te consisting of an array of 62 TeO2 crystals with a total active mass of 40:7 kg. The array is framed inside a dilution refrigerator, heavily shielded against environmental radioactivity and high-energy neutrons, and it is operated at a temperature of 8mK in the Gran Sasso Underground Laboratory. After several improvements the live time of the experiment is near 75%.

CUORICINO is an array of 62 TeO2 bolometers with a total mass of 40.7 kg (11.2 kg of 130Te), operated at about 10 mK to search for ββ(0ν) of 130Te. The detectors are organized as a 14-story tower and intended as a slightly modified version of one of the 19 towers of the CUORE project, a proposed tightly packed array of 988 TeO2 bolometers (741 kg of total mass of TeO2) for ultralow-background searches on neutrinoless double-beta decay, cold dark matter, solar axions, and rare nuclear decays. Started in April 2003 at the Laboratori Nazionali del Gran Sasso (LNGS), CUORICINO data taking was stopped in November 2003 to repair the readout wiring system of the 62 bolometers. Restarted in spring 2004, CUORICINO is presently the most sensitive running experiment on neutrinoless double-beta decay. No evidence for ββ(0ν) decay has been found so far and a new lower limit, T 1 2/0 ≥ 1.8 × 1024 yr (90% C.L.), is set, corresponding to 〈m ν〉 ≤ 0.2–1.1 eV, depending on the theoretical nuclear matrix elements used in the analysis. Detector performance, operational procedures, and background analysis results are reviewed. The expected performance and sensitivity of CUORE is also discussed.

CUORE (Cryogenic Underground Observatory for Rare Events) is an experiment proposed to infer the effective Majorana mass of the electron neutrino from measurements on neutrinoless double beta decay (0νDBD). The goal of CUORE is to achieve a background rate in the range 0.001 to 0.01 counts/keV/kg/y at the 0νDBD transition energy of 130Te (2528 keV). The proposed experiment, to be mounted in the underground Gran Sasso INFN National Laboratory, Italy, is realized by cooling about 1000 TeO2 bolometers, of 750 g each, at a temperature of 10mK. We will describe the experiment, to be cooled by an extremely powerful dilution refrigerator, operating with no liquid helium, and the main experimental features designed to assure the predicted sensitivity. We present moreover the last results of a small scale (40.7 kg) 0νDBD experiment carried on in the Gran Sasso Laboratory (CUORICINO).

CUORE is a 0.75 ton experiment to search for neutrinoless double beta decay of Te130 using 988 TeO2 bolometers. It aims at reaching a sensitivity on the effective neutrino mass of the order of few tens of meV. CUORICINO, a single CUORE tower running since 2003, plays an important role as a stand alone experiment and for developing the future CUORE setup. Present results already achieved and studies that are underway are here presented and discussed.

CUORICINO is an array of 62 TeO2 bolometers with a total mass of 40.7 Kg (10.4 Kg of 130Te), the largest operating one for a cryogenic experiment. Organized as a 14 storey tower, it is meant as a slightly modified version of one of the 25 towers of the CUORE project, a proposed tightly packed array of 1000 TeO2 bolometers (750 kg of total mass of TeO2) for ultralow-background searches on neutrinoless double beta decay, cold dark matter, solar axions, and rare nuclear decays. CUORICINO data taking started on April 2003 at the Laboratori Nazionali del Gran Sasso (LNGS) and was stopped in November 2003 to repair the readout wiring system of the 62 bolometers. Detector performance and early background analysis results are reviewed. Preliminary results on ββ(0ν) of 130Te are presented. The expected performance and sensitivity of CUORE is also discussed.

CUORE will be an observatory for rare events consisting of a tightly packed array of TeO2 bolometers, with a total mass of similar to 740 kg, operating in the underground Gran Sasso laboratory. A first step towards CUORE is CUORICINO, a running experiment with 40.7 kg of TeO2. Present results from CUORICINO for the neutrinoless double beta decay of Te-130 will be presented here (T-1/2(0 nu) >= 1.0x10(24) y, < m(nu)>

We review recent experimental data obtained with quasi-one-dimensional (1D) molecular magnets Gd(hfac) 3 NITR. For Gd(hfac) 3 NITiPr the results can be coherently explained only in terms of the Villain’s conjecture: a chiral order at intermediate temperatures and helical order at low temperatures. In the case of weakly frustrated molecular magnetic chain compounds Gd(hfac) 3 NITPh, new specific heat measurements show the presence of a phase transition to the three-dimensional (3D) helical order, observed at T ∼ 0.63 K. In the temperature range 25–250 mK the experimental specific heat data are reproduced very well by a simple spin wave theory.

Preliminary results on double beta decay (DBD) of 130Te, obtained in the first run of the CUORICINO experiment are presented. The set-up consists of an array of 62 crystals of TeO2 operating as bolometers in a deep underground dilution unit at a temperature of about 10 mK. Due to a total mass of about 41 kg, CUORICINO represents by far the most massive running cryogenic mass to search for rare events. The achieved lower limit on the neutrinoless DBD is 5.5·1023 years, that corresponds to a limit on the Majorana effective mass between 0.37 and 1.9 eV. Performances of the detectors together with the sensitivity estimation are discussed. © 2004 Elsevier B.V. All rights reserved.

CUORE is a proposed experiment, already partially funded, to search for 0ν-DBD of 130Te using 988 TeO2 bolometers. It aims at reaching a sensitivity on the effective neutrino mass of the order of few tens of meV. The crucial parameter on which this expectation is based is background. Different strategies are under development to reduce as much as possible its value, among which the comprehension of CUORICINO background, a single CUORE tower running since 2003, plays an important role. Present results already achieved and studies that are underway are here presented and discussed.

A new series of NTD Ge thermistors has been produced by the Lawrence Berkeley National Laboratory in the framework of the CUORE (Cryogenic Underground Observatory for Rare Events) experiment. The electrical characteristics of the new materials have been measured at the Departement of Physics of the University of Florence. The goal of this study was the choice of the best type of thermistor to use in the CUORE experiment. We report also the electrical resistivity, electron specific heat and electron-phonon decoupling of the NTD31 Ge material selected for CUORICINO (single CUORE module, which has become operative at the end of 2002).

After a short introduction on Double Beta Decay (DBD), general features of a bolometric experiment to search for neutrinoless Double Beta Decay (Ov-DBD) of Te-130 are outlined. The appeal of Te-130 as a DBD emitter is emphazized. After a brief description of the now closed Mi-DBD experiment, the CUORICINO experiment, an expansion of Mi-DBD, is presented and the first experimental results are given, together with a discussion on the background issues and the consequent sensitivity. CUORE experiment, a new generation Ov-DBD search, is proposed on the basis of the experience and information gathered with the realization and running of Mi-DBD and CUORICINO. The CUORE structure is presented and the ultimate sensitivity to Majorana neutrino mass is discussed. In case of inverse neutrino mass hierarchy, the CUORE discovery potential is shown to be large.

Milano collaboration has been developing for many years large mass bolometers for particle detection, and in particular for the study of neutrinoless double beta decay of 130 Te. The active components of the detectors are large mass (340 g and 790 g) TeO 2 crystals, while Neutron Transmutation Doped Ge thermistors are used as phonon sensors. These devices work at low temperatures, about 5-10 mK. The mechanical and thermal connections of the detector to the thermal bath are made with PTFE pieces that hold the crystal on copper frames. Gold wires are used as electric connections. We have developed a complete thermal model for the bolometers and "ad hoc" measurements of the thermal parameters involved were performed in the Florence cryogenic laboratory. These studies have permitted to simulate the static and dynamic behaviours of the detectors. A satisfactory agreement between simulated and the experimental response has been obtained as far as the static behaviour is concerned, while the dynamic behaviour is not yet fully understood. These preliminary results however will enable us to design new detector structures in order to improve the signal-to-noise ratio and the reproducibility. Given the good performances of these devices (excellent energy resolutions were obtained, of the order of 2 keV at 911 keV and of 5 keV at 2615 keV), this technique is particularly suitable to detectors for gamma ray spectroscopy. Encouraged by this results, the Milano-Como group has joined a large international collaboration for the realization of CUORE (Cryogenic Underground Observatory for Rare Events), seraching for Dark Matter and neutrinoless Double Beta Decay, a crucial phenomenon for neutrino physics. The Cuoricino detector, a small scale test of CUORE detector, is an array of 62 large mass bolometers like those already described, and it is now in operation in the Gran Sasso undergrand laboratory (Italy). It is the largest array of bolometric detectors ever constructed.

In this contribution, we describe two innovations of the structure of large mass bolometers, proposed by the cryogenic group of the Insubria University (Como) and developed in collaboration with the Firenze group. First, up to now, low temperature calorimeters do not have any sort of spatial resolution. This means that it is not possible to reject events coming from the material that faces the detectors (holder, refrigerators shields, ...). In order to cope this problem, we developed a new kind of composite bolometers able to discriminate, by means of active ultra-pure semiconductor shields, external surface events from those coming from the absorber bulk. A second innovation that we discuss here concerns the temperature sensors. Presently, neutron transmutation doped Ge thermistors are the most common kind of phonon sensors. Unfortunately, this kind of readout dissipates power on the detector because of the thermistor biasing and also introduces a Johnson noise term. To improve energy resolution we studied and test the application of capacitive sensors that in principle could allow us to achieve a better signal-to-noise ratio. Modeling, simulations and first encouraging measurements on surface sensitive bolometers will be discussed along with preliminary results on capacitive sensors.

CUORE is an experiment intended to investigate rare events like the double beta decay and the interaction of cold dark matter and solar axions. It consists of a tightly packed arrayof 1000 TeO2 bolometers, having a mass of 750 g each, operating in the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. A first step towards CUORE is CUORICINO, an experiment with 40.7 kg of TeO2 running since the beginning of 2003 in Gran Sasso. In this paper, the CUORE project is described, the first results of CUORICINO for the neutrinoless double beta decay of Te130 are given, and the physics potential and prospects of both CUORICINO and CUORE are presented.

CUORE is a new generation of 1-ton scale cryogenic detector for rare-events physics. CUORE, a detector to search Neutrinoless Double Beta Decay of 130Te, is an array of 988 TeO2 crystals of a mass of 750 g each. To build the cryogenic system, where the CUORE detector will be installed in the Gran Sasso Underground Laboratory, is really a challenge. It is a large cryogen-free cryostat cooled by pulse tubes and by a high power dilution refrigerator. To avoid radioactive background, about 10000 kg of lead will be cooled to below 1 K and only few construction materials are acceptable. the detector will have a total mass of about 1500 kg and must be cooled to less than 10 mK in a vibration-free environment.

International audience; There is currently great interest in the international metrological community for new accurate determinations of the Boltzmann constant k B , with the prospect of a new definition of the unit of thermodynamic temperature, the kelvin. In fact, k B relates the unit of energy (the joule) to the unit of the thermodynamic temperature (the kelvin). One of the most accurate ways to access the value of the Boltzmann constant is from measurements of the velocity of the sound in a noble gas. In the method described here, the experimental determination has been performed in a closed quasi-spherical cavity. To improve the accuracy, all the parameters in the experiment (purity of the gas, static pressure, temperature, exact shape of the cavity monitored by EM microwaves , etc.) have to be carefully controlled. Correction terms have been computed using carefully validated theoretical models, and applied to the acoustic and microwave signals. We report on two sets of isothermal acoustic measurements yielding the value k B = 1.380 647 74(171) × 10 −23 J · K −1 with a relative standard uncertainty of 1.24 parts in 10 6. This value lies 1.9 parts in 10 6 below the 2006 CODATA value (Mohr et al., Rev. Mod. Phys. 80, 633 (2008)), but, according to the uncertainties, remains consistent with it.