Purification of molybdenum, growth and characterization of medium volume ZnMoO₄crystals for the LUMINEU program

Abstract

The LUMINEU program aims at performing a pilot experiment on neutrinoless double beta decay of 100 Mo using radiopure ZnMoO 4 crystals operated as cryogenic scintillating bolometers. Growth of high quality radiopure crystals is a complex task, since there are no commercial molybdenum compounds available with the required level of purity and radioactive contamination. This paper discusses approaches to purify molybdenum and synthesize compounds for high quality radiopure ZnMoO 4 crystal growth. A combination of a double sublimation (with addition of zinc molybdate) with subsequent recrystallization in aqueous solutions (using zinc molybdate as a collector) was used. Zinc molybdate crystals up to 1.5 kg were grown by the low-thermal-gradient Czochralski technique; their optical, luminescent, diamagnetic, thermal and bolometric properties were tested.

The CUPID-Mo experiment for neutrinoless double-beta decay: performance and prospects

“…CUPID-Mo operates the four existing Li 2 100 MoO 4 crystals previously used in LUMINEU [28,29]. An additional sixteen new Li 2 100 MoO 4 crystals were fabricated with the identical procedure as that employed by LUMINEU [32,28,33]. All crystals have a cylindrical shape with ∼ 44 mm diameter and ∼ 45 mm height, and a mass of ∼ 0.2 kg.…”

“…purification of the ∼ 97% enriched molybdenum [32], previously used in the NEMO-3 experiment [34]; selection of lithium carbonate with low U/Th and 40 K content [28] and purified 100 Mo oxide [33]; crystal growth via a double crystallization process using the low-thermal-gradient Czochralski technique [33,28]; slicing of the scintillation elements, and treatment of their surfaces with radio-pure SiO powder.…”

Li2MoO4 Crystals Grown by Low-Thermal-Gradient Czochralski Technique

“…Deeply purified molybdenum oxide (MoO 3 ) [17] and commercial high purity lithium carbonate (Li 2 CO 3 , 99.99%) were used for solid-state synthesis of Li 2 MoO 4 according to the reaction: MoO 3 + Li 2 CO 3 = Li 2 MoO 4 + CO 2 ↑. The compound was kept for 5-10 h at a temperature of 450 C.…”

“…The intensive R&D in progress of molybdenum-containing scintillators is driven by the strong interest to the isotope 100 Mo, which is one of the most perspectives due to the high decay energy (Q 2 = 3034.40 (17) keV [10]), a possibility of mass scale isotopic enrichment (natural isotopic abundance  = 9.744(65)% [11]) and promising theoretical estimations of the decay probability (see, e.g., Ref. [6] and references therein beta decay experiment with a sensitivity on the level of the inverted hierarchy of the neutrino mass pattern [12,13].…”

Cryogenic phonon–scintillation detectors with PMT readout for rare event search experiments

“…Stringent requirements are imposed on the levels of intrinsic radioactivity of components used in the experimental setup [58]. Considerable effort is usually necessary to achieve the research aims regarding material selection [59], [60] purification [61] and production of detector components [62], [63] [64], aiming to reduce their intrinsic radioactivity levels. For the detector components themselves such requirements are obviously even more stringent.…”