A facility for mass production of ultra-pure NaI powder for the COSINE-200 experiment

COSINE-200 is the next phase of the ongoing COSINE-100 experiment. The main purpose of the experiment is the performance of an unambiguous verification of the annual modulation signals observed by the DAMA experiment. The success of the experiment critically depends on the production of a 200 kg array of ultra-pure NaI(Tl) crystal detectors that have lower backgrounds than the DAMA crystals. The purification of raw powder is the initial but important step toward the production of ultra-pure NaI(Tl) detectors. We have already demonstrated that fractional recrystallization from water solutions is an effective method for the removal of the problematic K and Pb elements. For the mass production of purified powder, a clean facility for the fractional recrystallization had been constructed at the Institute for Basic Science (IBS), Korea. Here, we report the design of the purification process, material recovery, and performance of the NaI powder purification facility.Comment: Proceeding for INSTR20, accepted in JINS

Preparation of low-radioactive high-purity enriched 100MoO3 powder for AMoRE-II experiment

This paper describes preparing radiopure molybdenum trioxide powder enriched with Mo-100 isotope for the AMoRE-II experiment. AMoRE-II, the second phase of the AMoRE experiments, will search for the neutrinoless double-beta decay (0νDBD) of the 100Mo isotope using over 100 kg of 100Mo embedded in 200 kg of ultra-pure Li2100MoO4 bolometric crystals. Efficient purification technology was developed and adapted to purify 100MoO3 powder with a 5 kg per month production capacity. Based on the ICP-MS analysis of purified powder, the 232Th and 238U were reduced to <9.4 μBq/kg and <50 μBq/kg, respectively. The concentrations of potassium, transition metals, and heavy metals were lower than 1 ppm. HPGe counting confirmed the reduction of progenies from the 232Th and 238U decay chains, reporting upper limits of <27 μBq/kg for 228Ac and <16 μBq/kg for 228Th. The 226Ra activity was acceptable at 110 ± 30 μBq/kg. In the last 3 years, 100 kg of pure 100MoO3 powder was produced. The production yield for the final purified product was above 90%, while irrecoverable losses were under 1.5%, and all by-products could be recycled further

Reduction of the radioactivity in sodium iodide (NaI) powder by recrystallization method

The COSINE experiment is searching for dark matter using ultra-low background NaI scintillating crystals. In order to reduce the internal contamination of the initial NaI powder to grow NaI crystals, NaI powder samples with different purities were purified by fractional recrystallization using de-ionized water. The concentrations of the main radioactive elements, K, Pb, Th, and U, which are major backgrounds for the dark matter search, were reduced to the level required for the experiment. Further, the concentrations of other impurities, e.g., Ba, Ca, Cr, and Fe, were also reduced, which is important to realize good quality NaI crystals. c.Akade´miai Kiado´ , Budapest, Hungary 201811sci

Thorium and uranium trace ICP-MS analysis for AMoRE project

AMoRE (Advanced Mo-based Rare process Experiment) is an international collaboration searching for the neutrinoless double-beta decay of the 100Mo isotope with cryogenic detectors using molybdate (100MoO4)-based scintillation crystals. The process requires that the detector apparatus and its components, including bolometric crystals and thus initial materials used for the crystal growth, be extremely low in radioactive isotopes having decays that may generate background noise signals in the region of interest. The present study summarizes an ICP-MS assay program conducted for the AMoRE experiment. Firstly, the 100MoO3 powder, the main component of the crystals, was studied in the analysis. Before crystal synthesis, enriched 100MoO3 powder was purified at the Center for Underground Physics (CUP). To ensure its radio purity, a sample preparation technique with a UTEVA® resin was developed for Th and U analysis with ICP-MS. The recovery yield was over 90% for the extraction procedure, and the detection limits for Th and U were 2.3 and 1.0 ppt, respectively. To determine the most appropriate material for the detector frame and shielding, several types of high-purity Cu were measured: Cu-OFE (Aurubis and Mitsubishi Materials) and Cu–NOSV (Aurubis). Similarly, a solid-phase extraction was applied for Th and U analysis, and detection limits were calculated at 0.1 and 0.2 ppt, respectively. The 3M Vikuiti™ ESR film, the closest part to the crystal in the detector assembly, was used as a light reflector. Two types of Vikuiti film, a roll and a sheet, were checked for radiopurity via full decomposition using a microwave ashing system. The procedural Detection Limits were achieved at a level of about 1 ppt. © 2023 Elsevier Ltd11Nsciescopu

Investigation of the molybdenum oxide purification for the AMoRE experiment

The presented study reports on the purification of molybdenum oxide, which is one of the important tasks of the Advanced Mo based Rare process Experiment in searching for the neutrinoless double beta (0 nu beta beta) decay of Mo-100. Purified MoO3 powder is used as initial material for further growth of radiopure monocrystals. As purification technique, double sublimation, co-precipitation with calcium chloride carrier, and precipitation of polyammonium molybdate from acidic media were used. Concentrations of impurities like Sr, Ba, Pb, Th and U were measured by ICP-MS and radioactive isotopes were checked by a HPGe detector at the YangYang underground Laboratory in Korea1111sciescopu

Reduction of radioactive elements in molybdenum trioxide powder by sublimation method and its technical performance

We studied the effectiveness of the purification of molybdenum trioxide (MoO3) powder with the sublimation method. To utilize the method, we have designed sublimation apparatus to purify the powder and annealing apparatus to collect the fine powder, followed by the wet chemistry method. As part of purification R&D, MoO3 powder was purified using a low vacuum sublimation method to remove radioactive elements such as Ra, Th, U, etc. The purification was performed at different temperatures to determine the optimum conditions for high decontamination factors and high recovery efficiencies. After applying the sublimation method, the powder was dissolved in aqueous ammonia; recrystallized to obtain polyammonium molybdate (PAM); and annealed to acquire MoO3 fine powder. The phase of MoO3 powder was studied by using X-ray diffraction (XRD) techniques. The effectiveness of the purification techniques was checked with inductively coupled plasma mass spectrometry (ICP-MS) measurements and the radioactivity from Ra, Th, and U were measured with high purity germanium (HPGe) detectors at Yangyang underground laboratory in Korea. The purified MoO3 powder was used by the AMoRE (Advanced Mo-based Rare process Experiment) collaboration to grow scintillating crystals. c 2019 IOP Publishing Ltd and Sissa Medialab11Nsciescopu

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

Growth and development of pure Li2MoO4 crystals for rare event experiment at CUP

© 2020 IOP Publishing Ltd and Sissa Medialab. The Center for Underground Physics (CUP) of the Institute for Basic Science (IBS) is searching for the neutrinoless double-beta decay (0 nu beta beta) of Mo-100 in the molybdate crystals of the AMoRE experiment. The experiment requires pure scintillation crystals to minimize internal backgrounds that can affect the 0 nu beta beta signal. For the last few years, we have been growing and studying Li2MoO4 crystals in a clean-environment facility to minimize external contamination during the crystal growth. Before growing (Li2MoO4)-Mo-100 crystal, we have studied (Li2MoO4)-Mo-nat crystal growth by a conventional Czochralski (CZ) grower. We grew a few different kinds of Li(2)(nat)MO(4)crystals using different raw materials in a campaign to minimize impurities. We prepared the fused Al2O3 refractories for the growth of ingots. Purities of the grown crystals were measured with high purity germanium detectors and by inductively coupled plasma mass spectrometry. The results show that the Li2MoO4 crystal has purity levels suitable for rare-event experiments. In this study, we present the growth of Li2MoO4 crystals at CUP and their purities11sci

Optimization of cryogenic calorimetric detection with lithium molybdate crystals for AMoRE-II experiments

© 2022 IOP Publishing Ltd and Sissa Medialab.The AMoRE collaboration is preparing for the second phase of the experiment, AMoRE-II, which will exploit a 100 kg of 100Mo isotopes to search for neutrinoless double beta decay from the isotope. Most of the 100Mo isotopes will be contained in the lithium molybdate (Li2MoO4) crystals, which will act as absorbers of cryogenic calorimeters coupled to MMC (metallic magnetic calorimeter) sensors. The detector array will have a total mass of approximately 200 kg with hundreds of detector modules. Hence, considerable effort has been taken to optimize the lithium molybdate crystal detector in terms of the detector performance and preparation procedure to build many detector modules in a reasonable schedule without compromising the detector performance. We found some critical experimental conditions to improve the energy resolution in a series of test experiments. In this paper, we discuss the effect of surface treatment and thermal link connection in improving the energy resolution from 14-15 keV to below 7 keV at 2.615 MeV, 208Tl gamma line, which is near the Q-value of the decay of 100Mo, 3.034MeV. We also report the high discrimination power for the separation of alpha particles using the simultaneous scintillation light detection with a test performed in the cryogen-free dilution refrigerator.11Nsciescopu