Zinc tungstate (ZnWO4) crystal scintillators are promising detection material for the experiments searching for double beta decay, dark matter, and investigating rare alpha decays. An extended R&D ...was performed to develop advanced quality ZnWO4 crystal scintillators. The R&D programme included the selection of the initial materials, the variation of the compound stoichiometry, the application of single and double crystallization, and the annealing of the crystal boules. The optical transmittance of the produced boules was measured, and the luminescence under X-ray excitation in the temperature region from 85 K to room temperature was studied (thermally stimulated luminescence was measured till 350 K). The energy resolution and the relative scintillation pulse amplitude were measured with gamma-sources demonstrating high scintillation properties of the samples produced by single crystallization from deeply purified zinc and tungsten oxides, with stoichiometric composition, annealed in air atmosphere.
The CUPID-Mo experiment at the Laboratoire Souterrain de Modane (France) is a demonstrator for CUPID, the next-generation ton-scale bolometric 0νββ experiment. It consists of a 4.2 kg array of 20 ...enriched Li2 100MoO4 scintillating bolometers to search for the lepton-number-violating process of 0νββ decay in 100Mo. With more than one year of operation (100Mo exposure of 1.17 kg × yr for physics data), no event in the region of interest and, hence, no evidence for 0νββ is observed. We report a new limit on the half-life of 0νββ decay in 100Mo of T1/2 > 1.5 × 1024 yr at 90% C.I. The limit corresponds to an effective Majorana neutrino mass ⟨m β β⟩ < (0.31 –0.54 ) eV, dependent on the nuclear matrix element in the light Majorana neutrino exchange interpretation.
The scintillation crystal bismuth germanate (BGO) is widely used in many applications. The unique technique developed in the Nikolaev Institute of Inorganic Chemistry, Novosibirsk, Russia, allows ...routine production of top quality large-sized BGO crystals. One of the important properties of a scintillation crystal is its radiation hardness. The intensive study of the radiation hardness of BGO crystals has been carried out by the collaboration of the Institutes of Siberian Branch of the Russian Academy of Science, Novosibirsk. The influence of the raw material purity and growth procedure on radiation hardness has been studied. The final tests of the crystal radiation hardness were performed by irradiating it with gamma rays from the radioactive source. The degradation of a light output of the best crystals is less than 10% after irradiation with doses of 10-100 krad expected in astrophysics experiments at a satellite. Based on the results of this study, the radiation hard BGO crystals for the "INTEGRAL" and "ASTRO-H" satellite missions have been made. A selfrecovery of the crystal light output is clearly seen. The time scale of the self recovery strongly depends on a dose of irradiation. It is days for 1 krad irradiation, weeks - for a 10 krad dose and a much longer period is required for 100 krad irradiation. All the crystals irradiated with a dose of 100 krad completely recover after annealing. The study reveals that there will be no essential degradation if this dose will be integrated over years of operation.
CUPID-Mo, located in the Laboratoire Souterrain de Modane (France), was a demonstrator for the next generation
0
ν
β
β
decay experiment, CUPID. It consisted of an array of 20 enriched Li
2
100
MoO
4
...bolometers and 20 Ge light detectors and has demonstrated that the technology of scintillating bolometers with particle identification capabilities is mature. Furthermore, CUPID-Mo can inform and validate the background prediction for CUPID. In this paper, we present a detailed model of the CUPID-Mo backgrounds. This model is able to describe well the features of the experimental data and enables studies of the
2
ν
β
β
decay and other processes with high precision. We also measure the radio-purity of the Li
2
100
MoO
4
crystals which are found to be sufficient for the CUPID goals. Finally, we also obtain a background index in the region of interest of 3.7
-
0.8
+
0.9
(stat)
-
0.7
+
1.5
(syst)
×
10
-
3
counts/
Δ
E
FWHM
/
mol
iso
/
year
,
the lowest in a bolometric
0
ν
β
β
decay experiment.
The CUPID-Mo experiment to search for 0
ν
β
β
decay in
100
Mo has been recently completed after about 1.5 years of operation at Laboratoire Souterrain de Modane (France). It served as a demonstrator ...for CUPID, a next generation 0
ν
β
β
decay experiment. CUPID-Mo was comprised of 20 enriched
Li
2
100
MoO
4
scintillating calorimeters, each with a mass of
∼
0.2
kg, operated at
∼
20
mK. We present here the final analysis with the full exposure of CUPID-Mo (
100
Mo exposure of 1.47
kg
×
year
) used to search for lepton number violation via 0
ν
β
β
decay. We report on various analysis improvements since the previous result on a subset of data, reprocessing all data with these new techniques. We observe zero events in the region of interest and set a new limit on the
100
Mo 0
ν
β
β
decay half-life of
T
1
/
2
0
ν
>
1.8
×
10
24
year (stat. + syst.) at 90% CI. Under the light Majorana neutrino exchange mechanism this corresponds to an effective Majorana neutrino mass of
m
β
β
<
(
0.28
-
0.49
)
eV, dependent upon the nuclear matrix element utilized.
The crystal growth of large high-quality inclusion-free CdWO4 crystals, 110 mm in diameter and mass up to 20kg, has been carried out by the Low Thermal Gradient Czochralski (LTG Cz) technique. The ...high-purity CdWO4(010) surface has been prepared by cleavage and high structural quality of the surface has been verified by RHEED, revealing a system of Kikuchi lines. The chemical state and electronic structure of the surface have been studied using X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). The total and partial densities of states of the CdWO4 tungstate were calculated employing the first-principles full potential linearized augmented plane wave (FP-LAPW) method. The results indicate that the principal contributors to the valence band of CdWO4 are the Cd 4d, W 5d and O 2p states which contribute mainly at the bottom, in the central portion and at the top of the valence band, respectively, with also significant contributions of the mentioned states throughout the whole CdWO4 valence-band region. With respect to the occupation of the O 2p states, the results of the FP-LAPW calculations are confirmed by comparison on a common energy scale of the XPS valence-band spectrum and the XES band representing the energy distribution of the O 2p states in this compound. Additionally, the FP-LAPW data allow us to conclude that the CdWO4 tungstate is a non-direct semiconductor.
Display omitted
•Large high-quality CdWO4 crystals, up to 115mm in diameter and mass up to 20kg, have been grown.•The high-purity cleaved CdWO4(010) surface has been studied by the XPS and XES methods.•The principal contributors to the CdWO4 valence band are the Cd 4d, W 5d and O 2p states.
New development of radiopure ZnWO4 crystal scintillators Belli, P.; Bernabei, R.; Borovlev, Yu.A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2019, Letnik:
935
Journal Article
Recenzirano
Odprti dostop
The residual radioactive contaminations of zinc tungstate crystal scintillators, produced by low-thermal-gradient Czochralski technique in various conditions, have been measured in the DAMA/R&D low ...background setup at the Gran Sasso National Laboratory (INFN, Italy). The total alpha activity has been measured in the detectors realized with different processes to vary between 158 and 1418 μBq/kg. The internal228Th contamination activity has been estimated as 0.34 μBq/kg in the most polluted crystal, while only upper limits for other ones have been set at level from < 0.17 μBq/kg to < 1.3 μBq/kg. These results open possibility for further radio-purifications of ZnWO4 crystal scintillators, which are of potential interests in various fields.
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