ZnMoO4: a promising bolometer for neutrinoless double beta decay searches

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 from 2.4 keV (at 238 keV) to 5.7 keV (at 2615 keV). The internal radioactive contaminations of the ZnMoO4 crystals were evaluated through a 407 hours background measurement. The obtained limit is < 32 microBq/kg for Th-228 and Ra-226. These values were used for a Monte Carlo simulation aimed at evaluating the achievable background level of a possible, future array of enriched ZnMoO4 crystals.Comment: 9 pages, 8 figure

Scintillating bolometers based on ZnMoO4 and Zn100MoO4 crystals to search for 0ν2β decay of 100Mo (LUMINEU project): first tests at the Modane Underground Laboratory

The technology of scintillating bolometers based on zinc molybdate (ZnMoO4) crystals is under development within the LUMINEU project to search for decay of 100Mo with the goal to set the basis for large scale experiments capable to explore the inverted hierarchy region of the neutrino mass pattern. Advanced ZnMoO4 crystal scintillators with mass of ∼0.3 kg were developed and Zn100MoO4 crystal from enriched 100Mo was produced for the first time by using the low-thermal-gradient Czochralski technique. One ZnMoO4 scintillator and two samples (59 g and 63 g) cut from the enriched boule were tested aboveground at milli-Kelvin temperature as scintillating bolometers showing a high detection performance. The first results of the low background measurements with three ZnMoO4 and two enriched detectors installed in the EDELWEISS set-up at the Modane Underground Laboratory (France) are presented

Growing of ZnWO₄ single crystals from melt by the low thermal gradient Czochralski technique

The shape formation regularities of ZnWO₄ scintillation crystals grown along the [001] and [010] directions by the low-temperature-gradient Czochralski technique have been studied. It has been established that increasing crystallization speed is accompanied by the development of faceted shapes at the crystallization front. The inclusion-free crystals can be grown with both completely rounded or completely faceted solid-liquid interface, while the coexistence of faceted and rounded surfaces may result in capturing inclusions at their boundaries. The inclusion-free ZnWO₄ crystals of 45 mm diameter and the length up to 150 mm have been grown. Absorption spectra of the crystals prior to and after annealing have been measured. For the samples of d40 and l=40 mm size, the energy resolution of 11 % for gamma radiation with the energy of 662 keV has been obtained.Досліджено закономірності формоутворення сцинтиляційних кристалів ZnWO₄ при їх рості низькоградієнтним методом Чохральського у напрямах [001] та [010]. Встановлено, що збільшення швидкості кристалізації супроводжується розвитком на фронті кристалізації огранованих форм. Кристали, вільні від включень, утворюються як при повністю округлому, так і при повністю ограненому фронті кристалізації, в той час як співіснування огранених та округлих форм може супроводжуватися захопленням включень на їхніх межах. Вирощено вільні від включень кристали ZnWO₄ діаметром 45 та довжиною до 150 мм. Виміряно спектри поглинання кристалів до та після їх відпалу. Для зразків d40 та l=40 мм одержано енергетичне розрішення 11 % для гамма-випромінювання з енергією 662 кеВ.Изучены закономерности формообразования сцинтилляционных кристаллов ZnWO₄ при их росте низкоградиентным методом Чохральского по направлениям [001] и [010]. Установлено, что повышение скорости кристаллизации сопровождается развитием на фронте кристаллизации гранных форм. Кристаллы, свободные от включений, образуются как при полностью округлом, так и при полностью гранном фронте кристаллизации, тогда как сосуществование гранных и округлых форм может сопровождаться захватом включений на их границах. Выращены свободные от включений кристаллы ZnWO₄ диаметром 45 и длиной до 150 мм. Измерены спектры поглощения кристаллов до и после их отжига. Для образцов размером d40 и длиной 40 мм получено энергетическое разрешение 11 % для гамма-излучения с энергией 662 keV

Recent progress in oxide scintillation crystals development by low-thermal gradient Czochralski technique for particle physics experiments

International audienceModern particle physics experiments call for high performance scintillation detectors with unique properties: radiation-resistant in high energy and astrophysics, highly radiopure, containing certain elements or enriched isotopes in astroparticle physics. The low-thermal gradient Czochralski (LTG CZ) crystal growth technique provides excellent quality large volume radiopure crystal scintillators. Absence of thermoelastic stress in the crystal and overheating of the melt in the LTG CZ method is particularly significant in production of crystalline materials with strong thermal anisotropic properties and low mechanical strength, with a very high yield of crystalline boules and low losses of initial charge, crucially important in production of crystal scintillators from enriched isotopes for double beta decay experiments. Here we discuss progress in development of the well known scintillators (Bi(4)Ge(3)O(12) (BGO), CdWO(4), ZnWO(4), CaMoO(4), PbMoO(4)), as well as R{&}D of new materials (ZnMoO(4), Li(2)MoO(4), Na(2)Mo(2)O(7)) for the next generation experiments in particle physics

The Na2W2O7 crystal: a crystal scintillator for dark matter search experiment

A single crystal of Na 2W 2O 7?(NWO) was grown by a low-thermal-gradient Czochralski technique (LTG-CZ). The scintillation properties of the crystal were evaluated for the first time as a potential material for dark matter search experiments. The luminescence and scintillation characteristics of the crystal were studied at room temperature and low temperatures by using a light-emitting diode (LED) and a 90Sr beta source. The luminescence and scintillation light yield at 10?K were significantly higher than those at room temperature. The crystal showed higher light yield at 10?K than a CaMoO4?(CMO) crystal. The decay time of the crystal was investigated at temperatures between 10 and 300?K. The sensitivity to spin-independent weakly interacting massive particle-nucleon interactions based on 10?kg (2?months) and 50?kg (12?months) data for the NWO crystal detectors was estimated by a simulated experiment using the standard halo model. The luminescence, scintillation, and sensitivity results revealed that the NWO crystal is a promising candidate for a dark matter search experiment in the near future. (c) 2018, The Author(s)11Nsciescopu

Preparation of Extra-pure Na2CO3 Powder with Crystallization Techniques for Low-Background Scintillation Crystal Growth

© 2020, Pleiades Publishing, Ltd. A method for the preparation of extra-pure Na2CO3 powder has been developed. The method is based on a fractional crystallization of Na2CO3 from its saturated solutions and its conversion into sodium formate, followed by a melt crystallization. To obtain the final product Na2CO3, the recrystallized sodium formate was thermally decomposed. The contents of Th and U in the purified powder were below 10 ppt, the concentrations of Mn, Co, Ba, and Pb were not above 3 ppb, the concentrations of Cu and Sr were on the level of tens of ppb, and the K concentration was about 200 ppb. The ICP-MS analysis showed that the purity of the obtained powder significantly surpasses that for commercial products in 99.997 and 99.999% purity grades. The sodium carbonate powder thus obtained is going to be used as initial material for growing scintillation single crystals in experiments searching for the neutrinoless double beta decay (0 nu beta beta) or dark matter11Nsciescopu