In the anisotropic scintillators the light output and the pulse shape for heavy particles (
p
,
α
, nuclear recoils) depend on the direction with respect to the crystal axes; the response to
γ
/
β
...radiation is isotropic instead. This feature offers the possibility to study the directionality approach, which is applicable in the particular case of those Dark Matter candidate particles inducing just nuclear recoils. Among the anisotropic scintillators, the ZnWO
4
has unique features, which make it an excellent candidate for this type of research, and there is still plenty of room for the improvement of its performances. In this paper the possibility of a low background pioneer experiment (named ADAMO—Anisotropic detectors for DArk Matter Observation) to exploit deep underground the directionality approach by using anisotropic ZnWO
4
scintillators is discussed.
We report on the development of scintillating bolometers based on lithium molybdate crystals that contain molybdenum that has depleted into the double-β active isotope 100Mo (Li2100deplMoO4). We used ...two Li2100deplMoO4 cubic samples, each of which consisted of 45-millimeter sides and had a mass of 0.28 kg; these samples were produced following the purification and crystallization protocols developed for double-β search experiments with 100Mo-enriched Li2MoO4 crystals. Bolometric Ge detectors were utilized to register the scintillation photons that were emitted by the Li2100deplMoO4 crystal scintillators. The measurements were performed in the CROSS cryogenic set-up at the Canfranc Underground Laboratory (Spain). We observed that the Li2100deplMoO4 scintillating bolometers were characterized by an excellent spectrometric performance (∼3–6 keV of FWHM at 0.24–2.6 MeV γs), moderate scintillation signal (∼0.3–0.6 keV/MeV scintillation-to-heat energy ratio, depending on the light collection conditions), and high radiopurity (228Th and 226Ra activities are below a few µBq/kg), which is comparable with the best reported results of low-temperature detectors that are based on Li2MoO4 using natural or 100Mo-enriched molybdenum content. The prospects of Li2100deplMoO4 bolometers for use in rare-event search experiments are briefly discussed.
A long-term measurement was conducted to search for α, double-α and double-β decays with γ quanta emission in naturally occurring osmium isotopes. This study took advantage of two ultra-low ...background HPGe detectors and one ultra-low background BEGe detector at the Gran Sasso National Laboratory (LNGS) of the INFN. Over almost 5 years of data were taken using high-purity osmium samples of approximately 173 g. The half-life limits set for α decays of
184
Os to the first 2
+
103.6 keV excited level of
180
W (
T
1/2
≥ 9.3 × 10
15
yr) and of
186
Os to the first 2
+
100.1 keV of
182
W (
T
1/2
≥ 4.8 × 10
17
yr) exceed substantially the present theoretical predictions that are at level of
T
1/2
~ (0.6–3) × 10
15
yr for
184
Os and
T
1/2
~ (0.3–2) × 10
17
yr for
186
Os. New half-life limits on the 2EC and ECβ
+
decay of
184
Os to the ground and excited levels of
184
W were set at level of
T
1/2
> 10
16
–10
17
yr; a lower limit on the 2β
–
decay of
192
Os to the 2
+
316.5 keV excited level of
192
Pt was estimated as
T
1/2
≥ 6.1 × 10
20
yr. The half-life limits for 2α decay of
189
Os and
192
Os were set for the first time at level of
T
1/2
> 10
20
yr.
Random coincidences of events could be one of the main sources of background in the search for neutrino-less double-beta decay of
100
Mo with macro-bolometers, due to their modest time resolution. ...Scintillating bolometers as those based on Li
2
MoO
4
crystals and employed in the CROSS and CUPID experiments can eventually exploit the coincident fast signal detected in a light detector to reduce this background. However, the scintillation provides a modest signal-to-noise ratio, making difficult a pile-up pulse-shape recognition and rejection at timescales shorter than a few ms. Neganov–Trofimov–Luke assisted light detectors (NTL-LDs) offer the possibility to effectively increase the signal-to-noise ratio, preserving a fast time-response, and enhance the capability of pile-up rejection via pulse shape analysis. In this article we present: (a) an experimental work performed with a Li
2
MoO
4
scintillating bolometer, studied in the framework of the CROSS experiment, and utilizing a NTL-LD; (b) a simulation method to reproduce, synthetically, randomly coincident two-neutrino double-beta decay events; (c) a new analysis method based on a pulse-shape discrimination algorithm capable of providing high pile-up rejection efficiencies. We finally show how the NTL-LDs offer a balanced solution between performance and complexity to reach background index
∼
10
-
4
counts/keV/kg/year with 280 g Li
2
MoO
4
(
100
Mo enriched) bolometers at 3034 keV, the Q
β
β
of the double-beta decay, and target the goal of a next generation experiment like CUPID.
•820 g LMO crystal grown by the Czochralski method.•LMO elastic properties and stress anisotropies evaluated.•Concave tail shape generates more stresses than convex ones.
A new technology for the ...mass production of lithium molybdate (Li2MoO4) crystals needed for the realization of the cryogenic neutrinoless double-beta decay detectors is under development within the framework of the CLYMENE project. Crystals with 4 and 5 cm in diameter were grown in two different Czochralski configurations. The first configuration, based on inductive heating of a RF coil coupled with a platinum crucible, was used to grow crystals of 4 cm in diameter. Bolometric tests performed with two samples cut from a 230 g crystal have shown less performances of the large sample (158 g), which had a cleavage, as compared to the small non-cracked sample (13.5 g). Numerical modeling was applied to investigate the temperature field in the furnace, the melt convection and thermo-elastic stresses in the crystal. Numerical results reveal 30% higher thermal stress at the bottom part of the ingot in the case of a concave shape of the crystal tail (experimental case) as compared to the case of a convex shaped tail. This could explain why the fracture started at the bottom part of the 230 g crystal boule, and highlights the importance of the crystal shape in the last stage of growth process. The furnace configuration used to grow 5 cm-diameter crystals was numerically optimized in order to reduce the thermal stress in the crystals. The first kg-mass Li2MoO4 ingot grown in the optimized configuration exhibit regular shape and good structural quality.
Neutrinoless double-beta (
0
ν
β
β
) decay is a hypothetical rare nuclear transition (
T
1
/
2
>
10
25
–
10
26
year). Its observation would provide an important insight into the nature of neutrinos ...(Dirac or Majorana particle) demonstrating that the lepton number is not conserved. This decay can be investigated with bolometers embedding the double-beta decay isotope (
76
Ge
,
82
Se
,
100
Mo
,
116
Cd
,
130
Te
...), which perform as low-temperature calorimeters (few tens of mK) detecting particle interactions via a small temperature rise read out by a dedicated thermometer. Cryogenic Rare-event Observatory with Surface Sensitivity (CROSS) aims at the development of bolometric detectors (based on
Li
2
MoO
4
and
TeO
2
crystals) capable of discriminating surface
α
and
β
interactions by exploiting superconducting properties of Al film deposited on the detector surface. We report in this paper the results of tests on prototypes performed at CSNSM (Orsay, France) that showed the capability of a-few-
μ
m
-thick superconducting Al film deposited on crystal surface to discriminate surface
α
from bulk events, thus providing the detector with the required pulse shape discrimination capability. The CROSS technology would further improve the background suppression and simplify the detector construction (no auxiliary light detector is needed to reject alpha surface events) with a view to future competitive double-beta decay searches.
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