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Particle Physics

Particle Physics

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Neutrinoless double-beta decay research (0ν2β)

Creation of a cryogenic scintillation detector based on 40Ca100MoO4 scintillation monocrystal using the enriched 100Mo isotope and Calcium, depleted in the 48Ca isotope for the AMoRE (Advanced Molybdenum-based Rare process Experiment) collaboration, within the project on a research for 100Mo isotope neutrinoless double-beta decay. The core target of the AMoRE collaboration is a research for the process of 100Mo isotope 0ν2β- decay: 100Mo → 100Ru + 2e- + 3.043 MeV (Q-value). Qββ = 3034 keV is the highest energy among the processes of isotopes double-beta decay, potentially produced by the centrifugal method in quantities of more than tens of hundreds of kilograms. To achieve sensitivity to the process of neutrinoless double-beta decay at the level of 1026 – 1027 years (which corresponds to the Majorana neutrino mass range ≈ 0.05 – 0.02 eV) a detector containing about 100 kg of the 100Мо isotope (about 500 40Ca100MoO4 scintillation elements) and having an excellent energy resolution < 0,5% (at the level of semiconductor detector resolution) is required. The detector material should contain ultra-low quantity of dangerous radioactive impurities (226Ra(214Bi) ≤ 0.1 mBq/kg, 228Th ≤ 0.05 mBq/kg). Calcium Molybdate crystal grown by Fomos-Materials has a variety of advantages, thanks to which it was chosen by scientists from the AMoRE collaboration. The physical advantages of the calorimetric detector are that «detector ≡ source» → high efficiency (⁓ 90%) of useful events detection; high operation isotope content (⁓ 50% in mass) in the compounding; obtaining the crystal by the Czochralski method allows to achieve high purity of the grown crystals → significant internal background reduction from 238U -, 232Th-series; energy resolution, comparable with the resolution for semiconductor detector (3 – 6 keV for the phonon mode), suppressed 100Mo 0ν2β- decay contribution; high light yield (up to 9300 photon/MeV); opportunity to analyze the signal in order to suppress α-background from the surface and near-surface contamination; possibility to increase the scale of experiments by cascade addition of monocrystals to the setup. As a result of studies and numerous works, the technology has been developed at Fomos-Materials. This technology allowed to grow 40Ca100MoO4 crystals and produce scintillation elements of them with the following dimensions (D (40-42) x (40-45)) mm, the mass of up to 300 g and light yield - LY = 9300 photon/MeV, which is comparable with the best Calcium Molybdate monocrystals, grown with natural raw materials; τrt = 16.5 µs at room temperature and τcr = 345 µs at 8 К and lower. Fomos-Materials has already produced scintillation elements for the first and second stages of the experiment (6 scintillation elements for the AMoRE Pilot with the total mass of 1.69 kg and 13 scintillation elements for the AMoRE I with the total mass of up to 5 kg).