This paper reports on the development of a technology involving$^{100}\hbox {Mo}$ -enriched scintillating bolometers, compatible with the goals of CUPID, a proposed next-generation bolometric experiment to search for neutrinoless double-beta decay. Large mass ( $\sim 1~\hbox {kg}$ ), high optical quality, radiopure$^{100}\hbox {Mo}$ -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 transition of$^{100}\hbox {Mo}$ (3034 keV) is 4–6 keV FWHM. The rejection of the $\alpha $ -induced dominant background above 2.6 MeV is better than $8\sigma $ . Less than $10~\upmu \hbox {Bq/kg}$ activity of$^{232}\hbox {Th}\, (^{228}\hbox {Th})$ and$^{226}\hbox {Ra}$ in the crystals is ensured by boule recrystallization. The potential of$^{100}\hbox {Mo}$ -enriched scintillating bolometers to perform high sensitivity double-beta decay searches has been demonstrated with only $10~\hbox {kg}\times \hbox {d}$ exposure: the two neutrino double-beta decay half-life of$^{100}\hbox {Mo}$ has been measured with the up-to-date highest accuracy as $T_{1/2}$ = [6.90 ± 0.15(stat.) ± 0.37(syst.)] $\times ~10^{18}~\hbox {years}$ . Both crystallization and detector technologies favor lithium molybdate, which has been selected for the ongoing construction of the CUPID-0/Mo demonstrator, containing several kg of$^{100}\hbox {Mo}$ .

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Development of $^{100}$Mo-containing scintillating bolometers for a high-sensitivity neutrinoless double-beta decay search

Bolometers are low temperature particle detectors with high energy resolution and detection efficiency. Some types of bolometric detectors are also able to perform an efficient particle identification. A wide variety of radiopure dielectric and diamagnetic materials makes the bolometric technique favorable for applications in astroparticle physics. In particular, thanks to their superior performance, bolometers play an important role in the worldwide efforts on searches for neutrinoless double-beta decay. Such experiments strongly require an extremely low level of the backgrounds that can easily mimic the process searched for. Here, we overview recent progress in the development of low background techniques for bolometric double-beta decay searches.

Low background techniques in bolometers for double-beta decay search

The Gran Sasso National Laboratories (LNGS) of the National Institute of Nuclear Physics (INFN) are equipped with an underground ultra-low background facility namely the SubTErranean Low Level Assay (STELLA), which is in first line dedicated to material screening for the fundamental physics experiments installed in the underground laboratories. The high level of performance of the ultra-low-level detector systems allows for detecting extremely low radioactivity levels in materials down to the μBq ⋅kg−1 level. The installations and experimental setups using ultra-low background techniques will be described shortly, and an example of material screening will be discussed.

Screening of materials with high purity germanium detectors at the Laboratori Nazionali del Gran Sasso

Inorganic crystal scintillators play a crucial role in particle detection for various applications in fundamental physics and applied science. The use of such materials as scintillating bolometers, which operate at temperatures as low as 10 mK and detect both heat (phonon) and scintillation signals, significantly extends detectors performance compared to the conventional scintillation counters. In particular, such low-temperature devices offer a high energy resolution in a wide energy interval thanks to a phonon signal detection, while a simultaneous registration of scintillation emitted provides an efficient particle identification tool. This feature is of great importance for a background identification and rejection. Combined with a large variety of elements of interest, which can be embedded in crystal scintillators, scintillating bolometers represent powerful particle detectors for rare-event searches (e.g., rare alpha and beta decays, double-beta decay, dark matter particles, neutrino detection). Here, we review the features and results of low-temperature scintillation detection achieved over a 30-year history of developments of scintillating bolometers and their use in rare-event search experiments.

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Scintillation in Low-Temperature Particle Detectors

A new R&D on lithium molybdate scintillators has begun within a project CLYMENE (Czochralski growth of Li 2 MoO 4 crYstals for the scintillating boloMeters used in the rare EveNts sEarches). One of the main goals of the CLYMENE is a realization of a Li 2 MoO 4 crystal growth line to be complementary to the one recently developed by LUMINEU in view of a mass production capacity for CUPID, a next-generation tonne-scale bolometric experiment to search for neutrinoless double-beta decay. In the present paper we report the investigation of performance and radiopurity of 158-g and 13.5-g scintillating bolometers based on a first large-mass (230 g) Li 2 MoO 4 crystal scintillator developed within the CLYMENE project. In particular, a good energy resolution (2–7 keV FWHM in the energy range of 0.2–5 MeV), one of the highest light yield (0.97 keV/MeV) amongst Li 2 MoO 4 scintillating bolometers, an efficient alpha particles discrimination (10 σ ) and potentially low internal radioactive contamination (below 0.2–0.3 mBq/kg of U/Th, but 1.4 mBq/kg of 210Po) demonstrate prospects of the CLYMENE in the development of high quality and radiopure Li 2 MoO 4 scintillators for CUPID.

First scintillating bolometer tests of a CLYMENE R&D on Li$_2$MoO$_4$ scintillators towards a large-scale double-beta decay experiment

https://hal.archives-ouvertes.fr/hal-01554702/document

Meryem Moutatouia

Papers

Exploratory growth in the Li2MoO4-MoO3 system for the next crystal generation of heat-scintillation cryogenic bolometers

Transport-magnetism correlation in layered perovskite manganite LaCaBiMn2O7