Among the detectors used for rare event searches, such as neutrinoless Double Beta Decay (0$ν$DBD) and Dark Matter experiments, bolometers are very promising because of their favorable properties (excellent energy resolution, high detector efficiency, a wide choice of different materials used as absorber, ...). However, up to now, the actual interesting possibility to identify the interacting particle, and thus to greatly reduce the background, can be fulfilled only with a double read-out (i.e. the simultaneous and independent read out of heat and scintillation light or heat and ionization). This double read-out could greatly complicate the assembly of a huge, multi-detector array, such as CUORE and EURECA. The possibility to recognize the interacting particle through the shape of the thermal pulse is then clearly a very interesting opportunity.
While detailed analyses of the signal time development in purely thermal detectors have not produced so far interesting results, similar analyses on macro-bolometers ($\sim$10-500 g) built with scintillating crystals showed that it is possible to distinguish between an electron or $γ$-ray and an $α$ particle interaction (i.e. the main source of background for 0$ν$DBD experiments based on the bolometric technique). Results on pulse shape analysis of a CaMoO$_4$ crystal operated as bolometer is reported as an example. An explanation of this behavior, based on the energy partition in the heat and scintillation channels, is also presented.
A 891 g BGO scintillating bolometer has been tested at 10 mK in the underground Laboratori Nazionali del Gran Sasso (Italy). The discrimination capability, the radio-purity of the compound and the main features of the crystal have been studied in order to demonstrate the excellent performances obtained by operating a scintillating bolometer in the field of gamma and alpha spectroscopy. The sensitivity of this detector in the study of extremely low surface contaminations has been investigated.
In the field of Double Beta Decay (DBD) searches, the use of high resolution detectors in which background can be actively discriminated is very appealing. Scintillating bolometers containing a Double Beta Decay emitter can largely fulfill this very interesting possibility. In this paper we present the latest results obtained with CdWO4 and CaMoO4 crystals. Moreover we report, for the first time, a very interesting feature of CaMoO4 bolometers: the possibility to discriminate beta-gamma events from those induced by alpha particles thanks to different thermal pulse shape.
本文介绍了研制双β衰变测辐射热计的结果。几个钼和镉基晶体进行了测试与测辐射热技术。通过第二个独立的测辐射热计测量闪烁光。对140 g CdWO_4晶体进行了417 h的寿命测量。由于闪烁光，α背景很容易区分，导致铊208的2615 keV伽马线以上的计数为零。这些结果与极其简单的光探测器操作相结合，代表了证明这种技术可行性的第一个切实证据。
ZnSe scintillating bolometers are good candidates for future Double Beta Decay searches, because of the 82Se high Q-value and thanks to the possibility of alpha background rejection on the basis of the scintillation signal. In this paper we report the characteristics and the anomalies observed in an extensive study of these devices. Among them, an unexpected high emission from alpha particles, accompanied with an unusual pattern of the light vs. heat scatter plot. The perspectives for the application of this kind of detectors to search for the Neutrinoless Double Beta Decay of 82Se are present…
We report the performances of a 0.51 kg CdWO4 scintillating bolometer to be used for future Double Beta Decay Experiments. The simultaneous read-out of the heat and the scintillation light allows to discriminate between different interacting particles aiming at the disentanglement and the reduction of background contribution, key issue for next generation experiments. We will describe the observed anticorrelation between the heat and the light signal and we will show how this feature can be used in order to increase the energy resolution of the bolometer over the entire energy spectrum, improv…
We present the performances of a 330 g zinc molybdate (ZnMoO4) crystal working as scintillating bolometer as a possible candidate for a next generation experiment to search for neutrinoless double beta decay of 100Mo. The energy resolution, evaluated at the 2615 keV gamma-line of 208Tl, is 6.3 keV FWHM. The internal radioactive contaminations of the ZnMoO4 were evaluated as <6 microBq/kg (228Th) and 27\pm6 microBq/kg (226Ra). We also present the results of the alpha vs beta/gamma discrimination, obtained through the scintillation light as well as through the study of the shape of the thermal s…
Zinc molybdate (ZnMoO4) single crystals were grown for the first time by the Czochralski method and their luminescence was measured under X ray excitation in the temperature range 85-400 K. Properties of ZnMoO4 crystal as cryogenic low temperature scintillator were checked for the first time. Radioactive contamination of the ZnMoO4 crystal was estimated as <0.3 mBq/kg (228-Th) and 8 mBq/kg (226-Ra). Thanks to the simultaneous measurement of the scintillation light and the phonon signal, the alpha particles can be discriminated from the gamma/beta interactions, making this compound extremely pr…
Large lithium molybdate (Li$_2$MoO$_4$) crystal boules were produced by using the low thermal gradient Czochralski growth technique from deeply purified molybdenum. A small sample from one of the boules was preliminary characterized in terms of X-ray-induced and thermally-excited luminescence. A large cylindrical crystalline element (with a size of $\oslash 40\times40$ mm) was used to fabricate a scintillating bolometer, which was operated aboveground at $\sim 15$ mK by using a pulse-tube cryostat housing a high-power dilution refrigerator. The excellent detector performance in terms of energy…
Lithium magnesium molybdate (Li$_2$Mg$_2$(MoO$_4$)$_3$) crystals were grown by the low-thermal-gradient Czochralski method. Luminescence properties of the material (emission spectra, thermally stimulated luminescence, dependence of intensity on temperature, phosphorescence) have been studied under X-Ray excitation in the temperature interval from 8 K to 400 K, while at the same being operated as a scintillating bolometer at 20 mK for the first time. We demonstrated that Li$_2$Mg$_2$(MoO$_4)_3$ crystals are a potentially promising detector material to search for neutrinoless double beta decay o…
Random coincidence of events (particularly from two neutrino double beta decay) could be one of the main sources of background in the search for neutrinoless double beta decay with cryogenic bolometers due to their poor time resolution. Pulse-shape discrimination by using front edge analysis, mean-time and $χ^2$ methods was applied to discriminate randomly coinciding events in ZnMoO$_4$ cryogenic scintillating bolometers. These events can be effectively rejected at the level of 99% by the analysis of the heat signals with rise-time of about 14 ms and signal-to-noise ratio of 900, and at the le…
Random coincidence of 2ν2β decay events could be one of the main sources of background for 0ν2β decay in cryogenic bolometers due to their poor time resolution. Pulse-shape discrimination by using front edge analysis, the mean-time and \c{hi}2 methods was applied to discriminate randomly coinciding 2ν2β events in ZnMoO4 cryogenic scintillating bolometers. The background can be effectively rejected on the level of 99% by the mean-time analysis of heat signals with the rise time about 14 ms and the signal-to-noise ratio 900, and on the level of 98% for the light signals with 3 ms rise time and s…
For the first time, a cadmium tungstate crystal scintillator enriched in $^{116}$Cd has been succesfully tested as a scintillating bolometer. The measurement was performed above ground at a temperature of 18 mK. The crystal mass was 34.5 g and the enrichment level ~82 %. Despite a substantial pile-up effect due to above-ground operation, the detector demonstrated a high energy resolution (2-7 keV FWHM in 0.2-2.6 MeV $γ$ energy range), a powerful particle identification capability and a high level of internal radiopurity. These results prove that cadmium tungstate is an extremely promising dete…
We present the performance of a 33 g Li2MoO4 crystal working as a scintillating bolometer. The crystal was tested for more than 400 h in a dilution refrigerator installed in the underground laboratory of Laboratori Nazionali del Gran Sasso (Italy). This compound shows promising features in the frame of neutron detection, dark matter search (solar axions) and neutrinoless double-beta decay physics. Low temperature scintillating properties were investigated by means of different alpha, beta/gamma and neutron sources, and for the first time the Light Yield for different types of interacting parti…
Random coincidences of nuclear events can be one of the main background sources in low-temperature calorimetric experiments looking for neutrinoless double-beta decay, especially in those searches based on scintillating bolometers embedding the promising double-beta candidate $^{100}$Mo, because of the relatively short half-life of the two-neutrino double-beta decay of this nucleus. We show in this work that randomly coinciding events of the two-neutrino double decay of $^{100}$Mo in enriched Li$_2$$^{100}$MoO$_4$ detectors can be effectively discriminated by pulse-shape analysis in the light …
A scintillating bolometer technology based on $^{100}$Mo-enriched lithium molybdate (Li$_2$$^{100}$MoO$_4$) crystals has been developed by LUMINEU to search for neutrinoless double-beta ($0ν2β$) decay of $^{100}$Mo. The results of several low temperature tests at underground environments have proved the reproducibility of high detector performance and crystal radiopurity: in particular $\sim$5--6~keV FWHM energy resolution and at least 9$σ$ rejection of $α$'s in the vicinity of the $0ν2β$ decay of $^{100}$Mo (3034 keV) and below 10~$μ$Bq/kg bulk activity of $^{228}$Th and $^{226}$Ra. A modest …
This paper reports on the development of a technology involving $^{100}$Mo-enriched scintillating bolometers, compatible with the goals of CUPID, a proposed next-generation bolometric experiment to search for neutrinoless double-beta decay. Large mass ($\sim$1~kg), high optical quality, radiopure $^{100}$Mo-containing zinc and lithium molybdate crystals have been produced and used to develop high performance single detector modules based on 0.2--0.4~kg scintillating bolometers. In particular, the energy resolution of the lithium molybdate detectors near the $Q$-value of the double-beta transit…
The technology of scintillating bolometers based on zinc molybdate (ZnMoO$_4$) crystals is under development within the LUMINEU project to search for 0$ν$2$β$ decay of $^{100}$Mo with the goal to set the basis for large scale experiments capable to explore the inverted hierarchy region of the neutrino mass pattern. Advanced ZnMoO$_4$ crystal scintillators with mass of $\sim$~0.3 kg were developed and Zn$^{100}$MoO$_4$ crystal from enriched $^{100}$Mo was produced for the first time by using the low-thermal-gradient Czochralski technique. One ZnMoO$_4$ scintillator and two samples (59 g and 63 …
Li$_2$$^{100\textrm{depl}}$MoO$_4$ Scintillating Bolometers for Rare-Event Search Experiments
National Research Centre Kurchatov Institute（库尔恰托夫国家研究中心研究所）；Nikolaev Institute of Inorganic Chemistry（尼古拉耶夫无机化学研究所）；Universidad Internacional de La Rioja（拉里奥哈国际大学）；INFN, Sezione di Milano Bicocca（意大利国家核物理研究院米兰比科卡分部）；INFN, Sezione di Roma（意大利国家核物理研究院罗马分部）；Institute for Nuclear Research of NASU（乌克兰国家科学院核物理研究所）；INFN Sezione di Roma Tor Vergata（意大利国家核物理研究院罗马托尔维尔加塔分部）；INFN, Laboratori Nazionali del Gran Sasso（意大利国家核物理研究院格兰萨索国家实验室）
The LUMINEU is designed to investigate the possibility to search for neutrinoless double beta decay in $^{100}$Mo by means of a large array of scintillating bolometers based on ZnMoO$_4$ crystals enriched in $^{100}$Mo. High energy resolution and relatively fast detectors, which are able to measure both the light and the heat generated upon the interaction of a particle in a crystal, are very promising for the recognition and rejection of background events. We present the LUMINEU concepts and the experimental results achieved aboveground and underground with large-mass natural and enriched cry…
We report in this paper the proofs that the pulse shape analysis can be used in some bolometers to identify the nature of the interacting particle. Indeed, while detailed analyses of the signal time development in purely thermal detectors have not produced so far interesting results, similar analyses on bolometers built with scintillating crystals seem to show that it is possible to distinguish between an electron or gamma-ray and an alpha particle interaction. This information can be used to eliminate background events from the recorded data in many rare process studies, especially Neutrinole…
Test of $^{116}$CdWO$_4$ and Li$_2$MoO$_4$ scintillating bolometers in the CROSS underground facility with upgraded detector suspension
Univ. Grenoble Alpes, CNRS, Grenoble INP (Institute of Engineering Univ. Grenoble Alpes), SIMAP（格勒诺布尔阿尔卑斯大学、法国国家科学研究中心、格勒诺布尔理工学院（格勒诺布尔大学工程学院）、SIMAP）；National Research Center Kurchatov Institute, Kurchatov Complex of Theoretical and Experimental Physics（库尔恰托夫研究所国家研究中心、理论与实验物理库尔恰托夫综合体）；Institute for Nuclear Research of NASU（乌克兰国家科学院核物理研究所）；INFN Laboratori Nazionali del Gran Sasso（意大利国家核物理研究院格兰萨索国家实验室）；Gran Sasso Science Institute（格兰萨索科学研究所）
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 Mo-100. We present the results of the alpha vs beta/gamma discrimination, obtained through the scintillation light as well as through the study of the shape of the thermal signal alone. The discrimination capability obtained at the 2615 keV line of Tl-208 is 8 sigma, using the heat-light scatter plot, while it exceeds 20 sigma using the shape of the thermal pulse alone. The achieved FWHM energy resolution ranges fro…
We present a method for detecting neutrons using scintillating lithium gadolinium borate crystal shards in a plastic matrix while maintaining high gamma rejection. We have procured two cylindrical detectors, 5"\times5", containing 1% crystal by mass. Crystal shards have a typical dimension of 1 mm. One detector was made with scintillating plastic, and one with nonscintillating plastic. Pulse shape analysis was used to reject gamma ray backgrounds. The scintillating detector was measured to have an intrinsic fast fission neutron efficiency of 0.4% and a gamma sensitivity of less than 2.3 \times…
In germanium-based light detectors for scintillating bolometers, a SiO$_2$ anti-reflective coating is often applied on the side of the germanium wafer exposed to light with the aim to improve its light collection efficiency. In this paper, we report about a measurement, performed in the temperature range 25-35 mK, of the light-collection increase obtained thanks to this method, which resulted to be of the order of 20%. The procedure followed has been carefully selected in order to minimize systematic effects. The employed light sources have the same spectral features (peaking at $\sim 630$ nm …
We present the search for Lorentz violation in the double beta decay of ^{82}Se~with CUPID-0, using an exposure of 9.95 kg x y. We found no evidence for the searched signal and set a limit on the isotropic components of the Lorentz violating coefficient of $\mathring{a}_{\text{of}}^{(3)} < 4.1\cdot10^{-6}$ GeV (90\% Credible Interval). This results is obtained with a Bayesian analysis of the experimental data and fully includes the systematic uncertainties of the model. This is the first limit on $\mathring{a}_{\text{of}}^{(3)}$ obtained with a scintillating bolometer, showing the potentiality…
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, and (3) it enhances the thermal signal induced in the light detector thanks to the extremely weak …
Scintillating bolometers of ZnSe are the baseline choice of the LUCIFER experiment, whose aim is to observe the neutrinoless double beta decay of 82Se. The independent read-out of the heat and scintillation signals allows to identify and reject alpha particle interactions, the dominant background source for bolometric detectors. In this paper we report the performances of a ZnSe crystal operated within the LUCIFER R&D. We measured the scintillation yield, the energy resolution and the background in the energy region where the signal from neutrinoless double beta decay of 82Se is expected with …
$TeO_2$ 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 $TeO_2$ bolometer to $α$'s emitted by $^{147}$Sm dissolved in the crystal at the growth phase. A Quenching Factor of ($1.0076\pm 0.0005$) is found, independent of the temperatu…
Two neutrino double $β$ decay can create irremovable background even in high energy resolution detectors searching for neutrinoless double $β$ decay due to random coincidence of $2\nu2β$ events in case of poor time resolution. Possibilities to suppress this background in cryogenic scintillating bolometers are discussed. It is shown that the present bolometric detector technologies enable to control this form of background at the level required to explore the inverted hierarchy of the neutrino mass pattern, including the case of bolometers searching for the neutrinoless double $β$ decay of $^{1…
This paper reports the detailed noise characterization, investigation of various noise sources and its mitigation to improve the performance of a cryogenic bolometer detector. The noise spectrum has been measured for a sapphire bolometer test setup with indigenously developed NTD Ge sensor in the CFDR system at Mumbai. The effect of external noise, arising either from ground loops in the system or from the diagnostic and control electronics of the cryostat, on the performance of a cryogenic bolometer is assessed. A systematic comparison of the influence of different noise pickups on the bolome…
Bolometers have proven to be very good detectors to search for rare processes thanks to their excellent energy resolution and their low intrinsic background. Further active background rejection can be obtained by the simultaneous readout of the heat and light signals produced by particles interacting in scintillating bolometers, as proposed by the LUCIFER experiment. In this framework, the choice of the light detector and the optimization of its working conditions play a crucial role. In this paper, we report a study of the performances of a Germanium bolometric light detector in terms of sign…
The CUORE experiment will search for neutrinoless double beta decay (0nDBD) of 130Te using an array of 988 TeO_2 bolometers operated at 10 mK in the Laboratori Nazionali del Gran Sasso (Italy). The detector is housed in a large cryogen-free cryostat cooled by pulse tubes and a high-power dilution refrigerator. The TeO_2 bolometers measure the event energies, and a precise and reliable energy calibration is critical for the successful identification of candidate 0nDBD and background events. The detector calibration system under development is based on the insertion of 12 gamma-sources that are …
This work describes a class of liquid scintillators that contain mostly water (>50 wt. % of the entire composition) and can discriminate between interactions induced by neutrons and gamma rays. By balancing the interface interactions between the components of the formulation, these scintillators form emulsions that can be thermodynamically stable. This approach, which considers a quantity known as the hydrophilic-lipophilic difference, requires consideration of the salinity and temperature as well as characterization of the surfactants and oil phase. Emulsions comprised of water and various oi…
The CUPID-0 experiment searches for neutrinoless double beta decay ($0νββ$) using the first array of enriched Zn$^{82}$Se scintillating bolometers with double (heat and light) read-out. To further enhance the CUPID-0 detector performances, the heat-light correlation has been exploited to improve the energy resolution. Different decorrelation algorithms have been studied and the best result is the average reduction of the full width at half maximum (FWHM) energy resolution to $(90.5\pm0.6)~\%$ of its original value , corresponding to a change from $\text{FWHM}=(20.7\pm0.5)~\text{keV}$ to $\text…
ZnMoO$_4$ scintillators with a mass of $\sim$ 0.3 kg, as well as Zn$^{100}$MoO$_4$ crystals enriched in the isotope $^{100}$Mo were produced for the first time by using the low-thermal-gradient Czochralski technique. The optical and luminescent properties of the produced crystals were studied to estimate the progress in crystal growth quality. The low-temperature tests with a 313 g ZnMoO$_4$ and two enriched Zn$^{100}$MoO$_4$ crystals were performed aboveground in the Centre de Sciences Nucléaires et de Sciences de la Matière. The low background measurements with a three ZnMoO$_4$ and two enri…
A successfull application of Geiger-mode multipixel avalanche diodes (GMAPDs) for pulse-shape discrimination in alpha-beta spectrometry using organic liquid scintillator is described in this paper. Efficient discrimination of alpha and beta components in the emission of radioactive isotopes is achieved for alpha energies above 0.3 MeV. The ultra-compact design of the scintillating detector helps to efficiently suppress cosmic-ray and ambient radiation background. This approach allows construction of hand-held robust devices for monitoring of radioactive contamination in various environmental c…
A comparative study of the neutron-$γ$ Pulse Shape Discrimination (PSD) with seven organic scintillators is performed using an identical setup and digital electronics. The scintillators include plastics (EJ-299-33 and a plastic prototype), single crystals (stilbene and the recent doped $p$-terphenyl) and liquids (BC501A, NE213 and the deuterated liquid BC537). First, the overall PSD performance of the different scintillators is compared and threshold neutron energies for a given discrimination quality are determined. Then, using statistical arguments, two intrinsic contributions to the PSD cap…
The LUCIFER project aims at deploying the first array of enriched scintillating bolometers for the investigation of neutrinoless double-beta decay of $^{82}$Se. The matrix which embeds the source is an array of ZnSe crystals, where enriched $^{82}$Se is used as decay isotope. The radiopurity of the initial components employed for manufacturing crystals, that can be operated as bolometers, is crucial for achieving a null background level in the region of interest for double-beta decay investigations. In this work, we evaluated the radioactive content in 2.5 kg of 96.3\% enriched $^{82}$Se metal…
CUPID-Mo is a cryogenic detector array designed to search for neutrinoless double-beta decay ($0νββ$) of $^{100}$Mo. It uses 20 scintillating $^{100}$Mo-enriched Li$_2$MoO$_4$ bolometers instrumented with Ge light detectors to perform active suppression of $α$ backgrounds, drastically reducing the expected background in the $0νββ$ signal region. As a result, pileup events and small detector instabilities that mimic normal signals become non-negligible potential backgrounds. These types of events can in principle be eliminated based on their signal shapes, which are different from those of regu…
High light collection efficiency is an important requirement in any application of scintillation detectors. The purpose of this study is to investigate the possibility for improving this parameter in cryogenic scintillation bolometers, which can be considered as a promising detectors in experiments investigating neutrinoless double beta decay and dark matter. Energy resolutions and relative pulse amplitudes of scintillation detectors using ZnWO4 scintillation crystals of different shapes (cylinder 20 mm in dimater by 20 mm and hexagonal prism with diagonal 20 mm and height 20 mm), reflector ma…
CUPID-Mo is a bolometric experiment to search for neutrinoless double-beta decay ($0νββ$) of $^{100}$Mo. In this article, we detail the CUPID-Mo detector concept, assembly, installation in the underground laboratory in Modane in 2018, and provide results from the first datasets. The demonstrator consists of an array of 20 scintillating bolometers comprised of $^{100}$Mo-enriched 0.2 kg Li$_2$MoO$_4$ crystals. The detectors are complemented by 20 thin cryogenic Ge bolometers acting as light detectors to distinguish $α$ from $γ$/$β$ events by the detection of both heat and scintillation light si…
The CUPID-Mo experiment is searching for neutrinoless double beta decay in $^{100}$Mo, evaluating the technology of cryogenic scintillating Li$_{2}^{100}$MoO$_4$ detectors for CUPID (CUORE Upgrade with Particle ID). CUPID-Mo detectors feature background suppression using a dual-readout scheme with Li$_{2}$MoO$_4$ crystals complemented by Ge bolometers for light detection. The detection of both heat and scintillation light signals allows the efficient discrimination of $α$ from $γ$&$β$ events. In this proceedings, we discuss results from the first 2 months of data taking in spring 2019. In addi…
