Radiopure ZnMoO4 scintillating bolometers for the LUMINEU double-beta experiment

International audience; The results of R&D of radiopure zinc molybdate (ZnMoO4) based scintillating bolometers for the LUMINEU (Luminescent Underground Molybdenum Investigation for NEUtrino mass and nature) double-beta decay experiment are presented. A dedicated two-stage molybdenum purification technique (sublimation in vacuum and recrystallization from aqueous solutions) and an advanced directional solidification method (the low-thermal-gradient Czochralski technique) were utilized to produce high optical quality large mass (∼1 kg) ZnMoO4 crystal boules and first 100Mo (99.5%) enriched Zn100MoO4 crystal scintillator (mass of ∼0.2 kg). Scintillating bolometers based on ZnMoO4 (≈ 0.33 kg) and Zn100MoO4 (≈ 0.06 kg) scintillation elements and high purity Ge wafers were tested in the EDELWEISS set-up at the Modane Underground Laboratory (France). Long term low temperature tests demonstrate excellent detectors’ performance and effectiveness of the purification and solidification procedures for the achievement of high radiopurity of the material, in particular with a bulk activity of 228Th and 226Ra below 4 µBq/kg. The adopted protocol was used to produce for the first time a large volume Zn100MoO4 crystal scintillator (mass of ∼1.4 kg, 100Mo enrichment is 99.5%) to search for neutrinoless double-beta decay of 100Mo in the framework of the LUMINEU project.