TeO2 Crystals Research Articles

CUORE crystal validation runs: Results on radioactive contamination and extrapolation to CUORE background

The CUORE Crystal Validation Runs (CCVRs) have been carried out since the end of 2008 at the Gran Sasso National Laboratories, in order to test the performance and the radiopurity of the TeO2 crystals produced at SICCAS (Shanghai Institute of Ceramics, Chinese Academy of Sciences) for the CUORE experiment. In this work the results of the first 5 validation runs are presented. Results have been obtained for bulk contaminations and surface contaminations from several nuclides. An extrapolation to the CUORE background has been performed.

The status of the CUORE experiment

The Cryogenic Underground Observatory for Rare Events (CUORE) is an experiment to search for neutrinoless double beta decay (0νββ) in 130Te and other rare processes. The observation of 0νββ would indicate that neutrinos are Majorana particles and would provide information about the absolute neutrino mass scale. CUORE is a bolometric detector composed of 988 TeO2 crystals, with the total mass of about 750 kg of Tellurium. We will discuss the status of the CUORE experiment, including recent R&D efforts, anticipated sensitivity, and present the most recent results from CUORICINO, the predecessor experiment operated in Gran Sasso National Laboratories in Italy.

Direct Dark Matter detection with CUORE

The Cryogenic Underground Observatory for Rare Events (CUORE) is an experiment to search for neutrinoless double beta decay in 130Te and other rare processes. CUORE is a bolometric detector composed of 988 TeO2 crystals, with the total mass of about 1 tonne. The large detector mass, low backgrounds, and the low energy threshold of a few keV make the experiment well suited for direct detection of galactic dark matter particles and solar axions. We discuss the development of a novel low-energy trigger that enables such searches, and present the preliminary results from a test run with four CUORE-like crystals at Gran Sasso National Laboratory in Italy.

Discrimination of α and β/γ interactions in a TeO2 bolometer

TeO2 crystals have proven to be superb bolometers for the search of neutrinoless double beta decay in many respects. However, if used alone, they do not exhibit any feature that allows to discriminate an α energy deposit from a β/γ one. This fact limits their ability to reject the background due to natural radioactivity and eventually affects the sensitivity of the search. In this paper we show the results of a TeO2 crystal where, in coincidence with its bolometric heat signal, also the luminescence light escaping the crystal is recorded. The results show that we are able to measure the light produced by β/γ particles, which can be explained as due to Cerenkov emission. No light is detected from α particles, allowing the rejection of this background source.

Performance of a large TeO2 crystal as a cryogenic bolometer in searching for neutrinoless double beta decay

Bolometers are ideal devices in the search for neutrinoless Double Beta Decay (0ν DBD). Enlarging the mass of individual detectors would simplify the construction of a large experiment, but would also decrease the background per unit mass induced by α-emitters located close to the surfaces and background arising from external and internal γ's.We present the very promising results obtained with a 2.13 kg TeO2 crystal. This bolometer, cooled down to a temperature of 10.5 mK in a dilution refrigerator located deep underground in the Gran Sasso National Laboratories, represents the largest thermal detector ever operated.The detector exhibited an energy resolution spanning a range from 3.9 keV (at 145 keV) to 7.8 keV (at the 2615 γ-line of 208Tl) FWHM. We discuss the decrease in the background per unit mass that can be achieved increasing the massof a bolometer.

Two-dimensional image edge enhancement by two-phonon Bragg diffraction

A model of acousto-optic interaction is developed for describing two-phonon Bragg diffraction in a gyrotropic single TeO2 crystal, which makes allowance for ellipticity of crystal opticaleigenwaves. Formation of a two-dimensional edge of an image in the first diffraction order is explained by invoking a three-dimensional description for the wave surfaces of optical eigenwaves.

Cryogenic Double Beta Decay Experiments: CUORE and CUORICINO

Cryogenic bolometers, with their excellent energy resolution, flexibility in material, and availability in high purity, are excellent detectors for the search for neutrinoless double beta decay. Kilogram-size single crystals of TeO2 are utilized in CUORICINO for an array with a total detector mass of 40.7 kg. CUORICINO currently sets the most stringent limit on the halflife of 130Te of T 1 / 2 0 ν ⩾ 2.4 × 10 24 yr (90% C.L.), corresponding to a limit on the effective Majorana neutrino mass in the range of 〈 m ν 〉 ⩽ 0.2 – 0.9 eV . Based on technology developed for CUORICINO and its predecessors, CUORE is a next-generation experiment designed to probe 〈 m ν 〉 in the range of 10–100 meV. Latest results from CUORICINO and overview of the progress and current status of CUORE are presented.

Signal and noise simulation of CUORE bolometric detectors

Bolometric detectors are used in particle physics experiments to search for rare processes, such as neutrinoless double beta decay and dark matter interactions. By operating at cryogenic temperatures, they are able to detect particle energies from a few keV up to several MeV, measuring the temperature rise produced by the energy released. This work focusses on the bolometers of the CUORE experiment, which are made of TeO2 crystals. The response of these detectors is nonlinear with energy and changes with the operating temperature. The noise depends on the working conditions and significantly affects the energy resolution and the detection performances at low energies. We present a software tool to simulate signal and noise of CUORE-like bolometers, including effects generated by operating temperature drifts, nonlinearities and pileups. The simulations agree well with data.

Calorimetry at 10mK

The search for neutrinoless double beta decay requires extreme technologies since the process searched is nearly impossibly rare. Calorimetric technique is one of the best promising line of attack to the problem expecially when the materials are operated at ultra-low temperatures as bolometers. This allows, at least in principle, the use of a large variety of different isotopes and a control of the main parameter dominating the game: the background index. In this paper we will discuss the CUORE calorimeter and the industrial processes with associated QC/QA for the production of radiopure TeO2 crystals and mention other type of materials that could suit even better the goal of this fundamental yet extremey difficult measurement.

Analysis of the Spectral Resolution of a TeO2 based Noncollinear Acousto-Optic Tunable Filter

The spectral resolution is a main index of evaluating the performance of the designed acousto-optic tunable filter (AOTF). In this letter, an accurate expression of the spectral resolution is presented by considering both the birefringence and the rotatory property of TeO2 crystal. The deduced expression is significant in improving the accuracy of the design of an AOTF and pushing the development of the high-performance AOTF.

Response of a TeO2 bolometer to α particles

TeO2 crystals are used as bolometers in experiments searching for Double Beta Decay without emission of neutrinos. One of the most important issues in this extremely delicate kind of experiments is the characterization of the background. The knowledge of the response to α particles in the energy range where the signal is expected is therefore a must. In this paper we report the results on the response function of a TeO2 bolometer to α's emitted by 147Sm dissolved in the crystal at the growth phase. A Quenching Factor of (1.0076±0.0005) is found, independent of the temperature in the investigated range. The energy resolution on α peaks shows a standard calorimeter energy dependence: σ [keV] = (0.56±0.02)⊕(0.010±0.002)√E[keV]. Signal pulse shape shows no difference between α and β/γ particles.

Acoustogyration diffraction of optical waves: case of SiO2 and TeO2 crystals

AbstractInteraction of acoustic and light waves with accounting for elastooptic and elastogyration effects is theoretically described. Collinear acoustogyration diffraction in quartz and paratellurite crystals is experimentally investigated and thoroughly analyzed. Piezogyration effect is experimentally studied for TeO2 crystals. The acoustogyration efficiency and the acoustogyration figure of merit calculated for a number of crystals (GaAs, TeO2 and SiO2) are shown to be too small for experimental detection. On the other hand, we demonstrate that the light diffraction at periodical distribution of the imaginary part of dielectric permittivity related to the piezogyration effect should, in principle, be observed for the case of interaction of optical waves with enantiomorphous ferroelastic domain structure and in cholesteric liquid crystals.

Characterization of the ablation of TeO2 crystals in air with femtosecond laser pulses

Femtosecond (fs) laser pulse ablation (pulse duration of 150 fs, wavelength of 775 nm, repetition rate of 1 kHz) of single-crystalline TeO2 surfaces was performed in air using the direct focusing technique. The lateral and vertical dimensions of laser ablated craters as well as the laser damage thresholds were evaluated for different pulse numbers applied to the same spot. The joint observation using optical microscopy, atomic force microscopy and scanning electron microscopy revealed the surface morphology of the ablated craters and also showed that the ablation threshold depends significantly on the number of laser pulses applied to the same spot due to incubation effects. The incubation effects change the absorption processes involved in fs-laser ablation of the transparent material from multiphoton absorption to a single-photon absorption. These results are discussed on the basis of recent models of the interaction of fs-laser pulses with dielectrics.

Status of CUORE and results from CUORICINO

CUORE (Cryogenic Underground Observatory for Rare Events) is a ton-scale bolometric experiment for the search of Neutrinoless Double Beta Decay of 130Te. The detector, an array of 988 TeO2 crystals arranged in 19 towers, will probe the Majorana nature of neutrino in the inverted mass-hierarchy region. Currently under construction at the Underground Gran Sasso National Laboratories, Italy, the experiment is foreseen to start data taking by 2012. The feasibility of CUORE was demonstrated by the recently completed pilot experiment CUORICINO, which set a lower limit on the Double Beta Decay time of 130Te of T 1 / 2 0 ν > 3.1 × 10 24 y . The status of CUORE and the results from CUORICINO will be presented.

Cerenkov emission as a positive tag of double beta decays in bolometric experiments

Active background reduction in high resolution calorimeters is a promising approach to achieve ultimate sensitivity in neutrinoless double beta decay experiments. We propose Cerenkov emission from beta rays in bolometric crystals as a viable alternative to scintillation. This novel approach could broaden the range of materials of interest for calorimetric searches of the double beta decay. We discuss the optical properties of TeO2 crystals, as a show case.

The cryostat of the CUORE Project, a 1-ton scale cryogenic experiment for Neutrinoless Double Beta Decay Research

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.

Experimental study of losses and cross talk in a multitransducer acousto-optic switch

A 2×2 switch based on an acousto-optic Bragg cell for telecommunications applications was developed. Two Bragg gratings are superimposed in the same crystal by applying two RF signals simultaneously to the cell. This results in the appearance of spurious optical beams. All the unwanted beam characteristics have been evaluated to optimize the performances of this device. The measurements have been made using an optical heterodyne detection method. The cell is made with a planar phased array transducer with a TeO2 crystal.

Design of the Cryogen-Free Cryogenic System for the CUORE Experiment

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.

Low Temperature Thermal Conductivity of Ti6Al4V Alloy

The CUORE detector, to be installed in 2010 at LNGS, is made of 988 TeO2 crystals to be cooled to 10 mK. It consists of a large cryogen-free cryostat cooled by five pulse tubes and one high-power specially designed dilution refrigerator (R. Ardito et al. in http://arxiv.org/abs/hep-ex/0501010, [2005]). The cryostat is ∼ 3 m high and has a diameter of ∼ 1.6 m. About 5 tons of lead shielding are to be cooled to below 1 K and a mass of 1.5 ton must be cooled to 10 mK.

Temperature dependence of the Brillouin frequency shift in crystals

In order to find a theoretical expression which most faithfully reproduces the temperature dependence of the Brillouin frequency shift in crystals, we have performed stimulated Brillouin spectroscopy in two crystals of TeO2 and PbMoO4 as test crystals by using a high precision Brillouin spectrometer with the frequency resolution of 20 kHz. In general, the temperature dependence of a Brillouin shift in crystals not undergoing phase transitions exhibits a linear negative slope at high temperatures and an asymptotic approach with zero slopes at low temperatures. We have experimentally confirmed that this temperature dependence stems from the temperature change of the elastic constant rather than the thermal changes of the refractive index and the volume expansion coefficient. It has been found that the Lakkad function based on Debye model and the Varshni function based on the Einstein model both reproduce quite well the temperature dependence of the Brillouin frequency shift in crystals.