Search

The experimental detection of the CE ν NS allows the investigation of neutrinos and neutrino sources with all-flavor sensitivity. Given its large content in neutrons and stability, Pb is a very appealing choice as target element. The presence of the radioisotope 210 Pb (T 1 / 2 ∼ 22 yrs) makes natural Pb unsuitable for low-background, low-energy event searches. This limitation can be overcome employing Pb of archaeological origin, where several half-lives of 210 Pb have gone by. We present results of a cryogenic measurement of a 15 g PbWO 4 crystal, grown with archaeological Pb (older than ∼ 2000 yrs) that achieved a sub-keV nuclear recoil detection threshold. A ton-scale experiment employing such material, with a detection threshold for nuclear recoils of just 1 keV would probe the entire Milky Way for SuperNovae, with equal sensitivity for all neutrino flavors, allowing the study of the core of such exceptional events. [ABSTRACT FROM AUTHOR]

We operated a PbMoO 4 scintillating cryogenic detector of 570 g, produced with archaeological lead. This compound features excellent low temperature characteristics in terms of light yield, 12 keV/MeV for β / γ interactions, and FWHM energy resolution, 11.7 keV at 2.6 MeV. Furthermore, the detector allows for an effective particle identification by means of pulse shape analysis on the heat read-out channel. The implementation of innovative techniques and procedures for the purification of raw materials used for the crystal growth, and the highly-pure archaeological Pb, allowed for the production of large volume high-quality crystal. The overall characteristics of the detector operated at cryogenic temperatures makes PbMoO 4 an excellent compound for neutrino physics applications, especially neutrinoless double-beta studies. [ABSTRACT FROM AUTHOR]

Bolometric detectors are excellent devices for the investigation of neutrinoless double-beta decay ( $$0\nu \beta \beta $$ ). The observation of such decay would demonstrate the violation of lepton number, and at the same time, it would necessarily imply that neutrinos are Majorana particles. The sensitivity of cryogenic detectors based on TeO $$_2$$ is strongly limited by the $$\alpha $$ -background in the region of interest for the 0 $$\nu \beta \beta $$ of $$^{130}$$ Te. It has been demonstrated that particle identification in TeO $$_2$$ bolometers is possible, measuring the Cherenkov light produced by particle interactions. However, the discrimination efficiency is low, and an event-by-event identification with NTD-based light detectors has to be demonstrated. We will discuss the performance of a highly sensitive light detector exploiting the Neganov-Luke effect for signal amplification. The detector, being operated with NTD thermistor and coupled to a 750 g TeO $$_2$$ crystal, shows the ability for an event-by-event identification of electron/gamma and $$\alpha $$ particles. The obtained results demonstrate the possibility to enhance the sensitivity of TeO $$_2$$ -based 0 $$\nu \beta \beta $$ experiment to an unprecedented level. [ABSTRACT FROM AUTHOR]

Abstract: The idea of using a scintillating bolometer was first suggested for solar neutrino experiments in 1989. After many years of developments, now we are able to exploit this experimental technique, based on the calorimetric approach with cryogenic particle detectors, to investigate rare events such as Neutrinoless Double Beta Decay and interaction of Dark Matter candidates. The possibility to have high resolution detectors in which a very large part of the natural background can be discriminated with respect to the weak expected signal is very appealing. The goal to distinguish the different types of interactions in the detector can be achieved by means of scintillating bolometer. The simultaneous read-out of the heat and scintillation signals made with two independent bolometers enable this precious feature leading to possible background free experiment. In the frame of the LUCIFER project we report on how exploiting this technique to investigate Double Beta Decay for different isotope candidates. Moreover we demonstrate how scintillating bolometers are suited for investigating other rare events such as decays of long living isotopes of lead and bismuth. [Copyright &y& Elsevier]

For the first time a Vanadium-based crystal was operated as cryogenic particle detector. The scintillating low temperature calorimetric technique was used for the characterization of a 22g YVO4 crystal aiming at the investigation of the 4-fold forbidden non-unique β- decay of 50V. The excellent bolometric performance of the compound together with high light output of the crystal make it an outstanding technique for the study of such elusive rate process. The internal radioactive contaminations of the crystal are also investigated showing that an improvement on the current status of material selection and purification are needed, 235/238U and 232Th are measured at the level of 28mBq/kg, 1.3 Bq/kg and 28m Bq/kg, respectively. In this work, we also discuss a future upgrade of the experimental set-up which may pave the road for the detection of the rare 50V β- decay. [ABSTRACT FROM AUTHOR]

We have developed and tested a new way of coupling bolometric light detectors to scintillating crystal bolometers based upon simply resting the light detector on the crystal surface, held in position only by gravity. This straightforward mounting results in three important improvements: (1) it decreases the amount of non-active materials needed to assemble the detector, (2) it substantially increases the light collection efficiency by minimizing the light losses induced by the mounting structure, (3) and it enhances the thermal signal induced in the light detector thanks to the extremely weak thermal link to the thermal bath. We tested this new technique with a 16 cm 2 Ge light detector with thermistor readout sitting on the surface of a large TeO 2 bolometer. The light collection efficiency was increased by greater than 50% compared to previously tested alternative mountings. We obtained a baseline energy resolution on the light detector of 20 eV RMS that, together with increased light collection, enabled us to obtain the best α vs β ∕ γ discrimination ever obtained with massive TeO 2 crystals. At the same time we achieved rise and decay times of 0.8 and 1.6 ms, respectively. This superb performance meets all of the requirements for the CUPID (CUORE Upgrade with Particle IDentification) experiment, which is a 1-ton scintillating bolometer follow up to CUORE. [ABSTRACT FROM AUTHOR]

High purity Zinc Selenide (ZnSe) crystals are produced starting from elemental Zn and Se to be used for the search of the neutrinoless double beta decay (0νDBD) of 82 Se. In order to increase the number of emitting nuclides, enriched 82 Se is used. Dedicated production lines for the synthesis and conditioning of the Zn 82 Se powder in order to make it suitable for crystal growth were assembled compliant with radio-purity constraints specific to rare event physics experiments. Besides routine check of impurities concentration, high sensitivity measurements are made for radio-isotope concentrations in raw materials, reactants, consumables, ancillaries and intermediary products used for ZnSe crystals production. Indications are given on the crystals perfection and how it is achieved. Since very expensive isotopically enriched material ( 82 Se) is used, a special attention is given for acquiring the maximum yield in the mass balance of all production stages. Production and certification protocols are presented and resulting ready-to-use Zn 82 Se crystals are described. [ABSTRACT FROM AUTHOR]

We present the performances of two 92% enriched 130 TeO 2 crystals operated as thermal bolometers in view of a next generation experiment to search for neutrinoless double beta decay of 130 Te. The crystals, 435 g each, show an energy resolution, evaluated at the 2615 keV γ -line of 208 Tl, of 6.5 and 4.3 keV FWHM. The only observable internal radioactive contamination arises from 238 U (15 and 8 μBq/kg, respectively). The internal activity of the most problematic nuclei for neutrinoless double beta decay, 226 Ra and 228 Th, are both evaluated as <3.1 μBq/kg for one crystal and <2.3 μBq/kg for the second. Thanks to the readout of the weak Cherenkov light emitted by β / γ particles by means of Neganov–Luke bolometric light detectors we were able to perform an event-by-event identification of β / γ events with a 95% acceptance level, while establishing a rejection factor of 98.21% and 99.99% for α particles. [ABSTRACT FROM AUTHOR]

Cryogenic detectors have a long history of success in the field of rare event searches. In particular scintillating calorimeters are very suitable detectors for this task since two signals are induced by a particle interaction in a scintillating crystal. The thermal signal provides a precise measurement of the deposited energy while the simultaneously measured scintillation light signal yields particle discrimination as the amount of produced scintillation light depends on the nature of the interacting particle. We investigate the calorimetric properties and background rejection capabilities of two large CsI (undoped) crystals (∼122 g each) operated as scintillating calorimeters at milli-Kelvin temperatures. Furthermore, we discuss the feasibility of this detection approach towards a future background-free dark matter experiment based on alkali halide crystals, with active particle discrimination via the two-channel detection. [ABSTRACT FROM AUTHOR]

Abstract We present here an innovative cryogenic light detector capable to measure a few tens of eV signal thanks to the amplification assisted by the Neganov–Luke effect. The thermal signal boost in the presence of an electric field allows us to improve the signal-to-noise ratio reaching a baseline noise of around 20 eV. This device – coupled to an enriched 130 TeO 2 bolometer (435 g) – registered 160 eV Cherenkov light signal induced by 2615 keV 208Tl with a signal to noise ratio about 6:1. Since α particles emitted in decays of natural radionuclides do not produce the Cherenkov radiation, we were able to achieve an efficient α ∕ γ separation in the region of interest for neutrinoless double beta decay of 130Te (Q -value is 2527 keV). Specifically, a rejection factor of 99.9% for α particles was obtained with a 98.3% acceptance of β ∕ γ events. The achieved α rejection efficiency is required to reduce the dominant α background in the follow-up of the CUORE experiment (CUPID), a ton-scale bolometric search with particle identification. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented regarding a 71-year-old man prescribed with a single oral dose of acetazolamide after cataract surgery in which an ocular coherence tomography (OCT) scans that revealed bilateral angleclosure glaucoma (ACG).

In this article we report on a detailed study of the internal radioactive and chemical contamination of the Li 6 Eu(BO 3) 3 scintillating crystal operated as a cryogenic scintillating bolometer over 359 h. The excellent discrimination power of the detector allows to distinguish effectively beta/gamma events from alpha events. Whilst a weak activity of daughter nuclides from U/Th chains at the level few mBq/kg was observed, this crystal was found to be significantly contaminated by 147Sm, an alpha-active nuclide, at the level of about 0.5 Bq/kg. The light yield for β / γ events was determined to be 7.4(6) keV/MeV. The light yield and quenching factor for alpha particles vary in the range of (0.5–1.2) keV/MeV and (0.07–0.17), respectively, due to energy dependence of the emitted scintillating light in the energy interval (2.0–7.0) MeV. The integral luminescence intensity of the Li 6 Eu(BO 3) 3 crystal increases by more than four times only at low temperatures, below 80 K. Therefore, the Li 6 Eu(BO 3) 3 -based cryogenic scintillating bolometers can be attractive detectors for direct neutron flux monitoring, to search for rare alpha decays or solar axions. [ABSTRACT FROM AUTHOR]

In the view of exploring the inverted hierarchy region future experiments investigating the neutrinoless double beta decay have to demand for detectors with excellent energy resolution and zero background in the energy region of interest. Cryogenic scintillating bolometers are very suitable detectors for this task since they provide particle discrimination: the simultaneous detection of the phonon and light signal allows us to identify the interacting type of particle and thus guarantees a suppression of $$\alpha $$ -induced backgrounds, the key-issue for next-generation tonne-scale bolometric experiments. The LUCIFER project aims at running the first array of enriched scintillating Zn $$^{\text {82}}$$ Se bolometers (total mass of about 8kg of $$^{\text {82}}$$ Se) with a background level as low as 10 $$^{\text {--3}}$$ counts/(keV kg y) in the energy region of interest. The main effort is currently focused on the finalization of the crystal growth procedure in order to achieve high quality Zn $$^{\text {82}}$$ Se crystals both in terms of radiopurity and bolometric properties. We present results from tests of such crystals operated at mK temperatures which demonstrate the excellent background rejection capabilities of this detection approach towards a background-free demonstrator experiment. Besides, the high purity of the enriched $$^{\text {82}}$$ Se material allows us to establish the most stringent limits on the half-life of the double beta decay of $$^{\text {82}}$$ Se on excited levels. [ABSTRACT FROM AUTHOR]

The detection of $$^{148}$$ Sm alpha decay with a precise measured half-life of $$\left( {6.4_{-1.3}^{+1.2} }\right) \times 10^{15}y$$ and a Q-value of 1987.3 $$\pm $$ 0.5 keV was achieved by a new experimental approach, where a conventional ZnWO $$_{4}$$ scintillating crystal doped with enriched $$^{148}$$ Sm isotope is operated as a cryogenic scintillating bolometer (phonon and light channel) at mK-temperatures. [ABSTRACT FROM AUTHOR]

An active discrimination of the dominant α -background is the prerequisite for future neutrinoless double-beta decay experiments based on TeO 2 bolometers. We investigate such α -particle rejection in cryogenic TeO 2 bolometers by the detection of Cherenkov light. For a setup consisting of a massive TeO 2 crystal (285 g) and a separate cryogenic light detector, both using transition edge sensors as temperature sensors operated at around 10 mK, we obtain an event-by-event identification of e/ γ - and α -events. We find in the energy interval ranging from 2400 keV to 2800 keV and covering the Q-value of the neutrinoless double-beta decay of 130 Te a separation of the means of the two populations of 3.7 times their width. [ABSTRACT FROM AUTHOR]

Abstract: A methodological approach based on Monte Carlo code for the neutronic analysis of the TRIGA Mark II research reactor of the University of Pavia in the configuration of cold and clean nuclear fuel is presented. The complete implementation of the code is based on the construction characteristics with the validation of the results obtained by benchmarking the experimental and operational data reported in the reactor Fist Criticality Final Report. The 3-D continuous-energy Monte Carlo code MCNP5 was used. The description of the geometrical structure of the reactor core and the fuel configuration were designed with great accuracy and good detail. The comparison between simulated and measured data allows the creation of a complete reconstruction model of the TRIGA Mark II reactor. [Copyright &y& Elsevier]

Abstract: The neutron flux is a crucial parameter for the analysis of nuclear reactors, because it affects the reaction rate and thus the fuel burnup. Moreover, a very precise knowledge of the flux in the irradiation positions is helpful for benchmarking the simulation models of the reactor. In particular, an MCNP model of the TRIGA Mark II reactor installed at LENA (Laboratory of Applied Nuclear Energy) of the University of Pavia was developed in the recent years, describing the geometries and the materials of the whole reactor with very good accuracy. In this article, we present the results of the neutron flux measurements in four irradiation positions. The neutron activation technique was used to perform an absolute measurement of the flux. Various samples containing a known amount of elements were irradiated in the reactor facilities and the activation rate of a large number of isotopes was measured through γ-ray spectroscopy with very low background HPGe detectors. In order to accurately calculate the activation rate, Monte Carlo codes based on GEANT4 were developed to evaluate the γ-ray detection efficiency for every radioisotope of interest. The samples were measured with three different HPGe detectors and the measurements were repeated in various geometric configurations in order to assess the reliability and repeatability of this analysis technique. The MCNP reactor model was used to evaluate the energetic neutron flux distributions in the irradiation positions. The effective activation cross sections were computed from these distributions, testing the dependence on the MCNP simulation results. Finally, the neutron flux was calculated from the data of activation rate and effective cross section of each isotope. The good agreement in the results of the flux calculations from the many different activated samples confirms the reliability of the adopted methodology. [Copyright &y& Elsevier]

In the field of fundamental particle physics, the neutrino has become more and more important in the last few years, since the discovery of its mass. In particular, the ultimate nature of the neutrino (if it is a Dirac or a Majorana particle) plays a crucial role not only in neutrino physics, but also in the overall framework of fundamental particle interactions and in cosmology. The only way to disentangle its ultimate nature is to search for the neutrinoless double beta decay. The idea of LUCIFER is to combine the bolometric technique proposed for the CUORE experiment with the bolometric light detection technique used in cryogenic dark matter experiments. The bolometric technique allows an extremely good energy resolution while its combination with the scintillation detection offers an ultimate tool for background rejection. The goal of LUCIFER is not only to build a background-free small-scale experiment but also to directly prove the potentiality of this technique. Preliminary tests on several detectors containing different interesting DBD emitters have clearly demonstrated the excellent background rejection capabilities that arise from the simultaneous, independent, double readout of heat and scintillation light. [ABSTRACT FROM AUTHOR]

We present the performances of a 330 g zinc molybdate (ZnMoO) crystal working as scintillating bolometer as a possible candidate for a next generation experiment to search for neutrinoless double beta decay of Mo. The energy resolution, evaluated at the 2615 keV γ-line of Tl, is 6.3 keV FWHM. The internal radioactive contaminations of the ZnMoO were evaluated as <6 μBq/kg (Th) and 27±6 μBq/kg (Ra). We also present the results of the α vs β/ γ discrimination, obtained through the scintillation light as well as through the study of the shape of the thermal signal alone. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the performances of two ZnMoO4 scintillating crystals operated as bolometers, in view of a next generation experiment to search the neutrinoless double beta decay of 100Mo. We present the results of the α vs β/γ discrimination, obtained through the scintillation light as well as through the study of the shape of the thermal signal alone. The separation obtained at the 2615keV line of 208Tl is 8σ, using the heat-light scatter plot, while it exceeds 20σ using the shape of the thermal pulse alone. The achieved FWHM energy resolution ranges from 2.4keV (at 238keV) to 5.7keV (at 2615keV). The internal radioactive contaminations of the ZnMoO4 crystals were evaluated through a 407h background measurement. The obtained limit is <32μBq/kg for 228Th and 226Ra. These values were used for a Monte Carlo simulation aimed at evaluating the achievable background level of a possible, future array of enriched Zn100MoO4 crystals. [Copyright &y& Elsevier]

209Bi alpha decay to the ground and to the first excited state have been recently observed for the first time with a large BGO scintillating bolometer. The half-life of 209Bi is determined to be τ1/2 = (2.01 ± 0.08) X 1019 yr while the branching ratio for the ground-state to ground-state transition is (98.8 ± 0.3)%. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this work was to develop a methodological approach based on Monte Carlo code for the neutronic analysis of the first core configuration of the TRIGA Mark II research reactor of the University of Pavia and the validation of the results by benchmarking with the experimental and operational data reported in the reactor Fist Criticality Final Report. The neutron analysis was realised by means of the 3-D continuous-energy Monte Carlo code MCNP4C. The reactor model implemented represents in good detail all core components and allows the description of different core and fuel configurations with good versatility. Continuous-energy cross section data from ENDF/B-VI and ENDF/B-V and S(α, β) scattering functions from the ENDF/B-VI library were used. The results of the MCNP simulations and the experimental values show a very good agreement proving the goodness of the model. [Copyright &y& Elsevier]

Large-mass bolometers are today extensively used for dark matter and double beta decay searches, in both cases the ultimate experimental sensitivity is defined by the background level reached in such devices. The most common background sources and the techniques used for their identification and reduction are here reviewed, with a particular focus on double beta decay searches. The relevant role played by Monte Carlo simulations in this field is discussed. As a real case, the background optimization in the MiDBD experiment is described. [ABSTRACT FROM AUTHOR]

For rare event searches, such as the direct dark matter search experiment CRESST (Cryogenic Rare Event Search with Superconducting Thermometers), highly sensitive cryogenic detectors are indispensable. A very low energy threshold (≪ 100 eV) and excellent energy resolution are required to increase the experimental sensitivity, particularly for low mass dark matter particles (m DM < 5 GeV/c 2), and to differentiate between these rare events and natural radioactive backgrounds. For background suppression, CRESST benefits from using simultaneously two detection channels from scintillating calorimeters, in this case of heat and light. Measuring a heat signal and its corresponding scintillating light, allows event-by-event particle identification down to certain energies. Therefore, the development of cryogenic light detectors that can achieve single photon sensitivity, have high radio-purity and excellent energy resolution, is a key point to improve the experiment's sensitivity at low energies. In this contribution we explain and report on novel ways to improve the light collection efficiency through a preliminary study on Nb films sputtered on Sapphire and through highly doped Si as cryogenic light detectors. [ABSTRACT FROM AUTHOR]

The large statistics collected during the operation of a ZnMoO4 array, for a total exposure of 1.3 kg day of 100Mo, allowed the first bolometric observation of the two neutrino double beta decay of 100Mo. The observed spectrum of each crystal was reconstructed taking into account the different background contributions due to environmental radioactivity and internal contamination. The analysis of coincidences between the crystals allowed the assignment of constraints to the intensity of the different background sources, resulting in a reconstruction of the measured spectrum down to an energy of ∼300 keV. The half-life extracted from the data is T = [7.15 ± 0.37 (stat) ± 0.66 (syst)] × 1018 y. [ABSTRACT FROM AUTHOR]

We report on the first compelling observation of α decay of 151Eu to the ground state of 147Pm. The measurement was performed using a 6.15 g Li6Eu(BO3)3 crystal operated as a scintillating bolometer. The Q-value and half-life measured are: Q = 1948.9±6.9(stat.) ± 5.1(syst.) keV, and T1/2 = (4.62 ± 0.95(stat.) ± 0.68(syst.)) × 1018 y. The half-life prediction of nuclear theory using the Coulomb and proximity potential model are in good agreement with this experimental result. [ABSTRACT FROM AUTHOR]