Neutron and muon-induced background studies for the AMoRE double-beta decay experiment

© 2019 Elsevier B.V.AMoRE (Advanced Mo-based Rare process Experiment) is an experiment to search a neutrinoless double-beta decay of 100Mo in molybdate crystals. The neutron and muon-induced backgrounds are crucial to obtain the zero-background level (<10−5 counts/(keV · kg · yr)) for the AMoRE-II experiment, which is the second phase of the AMoRE project, planned to run at YEMI underground laboratory. To evaluate the effects of neutron and muon-induced backgrounds, we performed Geant4 Monte Carlo simulations and studied a shielding strategy for the AMORE-II experiment. Neutron-induced backgrounds were also included in the study. In this paper, we estimated the background level in the presence of possible shielding structures, which meet the background requirement for the AMoRE-II experiment11sciescopu

Measurement of the Background Activities of a 100Mo-enriched Powder Sample for an AMoRE Crystal Material by using Fourteen High-Purity Germanium Detectors

The Advanced Molybdenum-based Rare process Experiment in its second phase (AMoRE-II) will search for neutrinoless double-beta (0{\nu}\b{eta}\b{eta}) decay of 100Mo in 200 kg of molybdate crystals. To achieve the zero-background level in the energy range of the double-beta decay Q-value of 100Mo, the radioactive contamination levels in AMoRE crystals should be low. 100EnrMoO3 powder, which is enriched in the 100Mo isotope, is used to grow the AMoRE crystals. A shielded array of fourteen high-purity germanium detectors with 70% relative efficiency each was used for the measurement of background activities in a sample of 9.6-kg powder. The detector system named CAGe located at the Yangyang underground laboratory was designed for measuring low levels of radioactivity from natural radioisotopes or cosmogenic nuclides such as 228Ac, 228Th, 226Ra, 88Y, and 40K. The activities of 228Ac and 228Th in the powder sample were 0.88 \pm 0.12 mBq/kg and 0.669 \pm 0.087 mBq/kg, respectively. The activity of 226Ra was measured to be 1.50 \pm 0.23 mBq/kg. The activity of 88Y was 0.101 \pm 0.016 mBq/kg. The activity of 40K was found as 36.0 \pm 4.1 mBq/kg.Comment: 24 pages, 10 figures, 5 table

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 &lt;9.4 μBq/kg and &lt;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 &lt;27 μBq/kg for 228Ac and &lt;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

Search for sterile neutrino oscillation using RENO and NEOS data

We present a reactor model independent search for sterile neutrino oscillation using 2\,509\,days of RENO near detector data and 180 days of NEOS data. The reactor related systematic uncertainties are significantly suppressed as both detectors are located at the same reactor complex of Hanbit Nuclear Power Plant. The search is performed by electron antineutrino\,($\overline{\nu}_e$) disappearance between six reactors and two detectors with baselines of 294\,m\,(RENO) and 24\,m\,(NEOS). A spectral comparison of the NEOS prompt-energy spectrum with a no-oscillation prediction from the RENO measurement can explore reactor $\overline{\nu}_e$ oscillations to sterile neutrino. Based on the comparison, we obtain a 95\% C.L. excluded region of $0.1<|\Delta m_{41}^2|<7$\,eV$^2$. We also obtain a 68\% C.L. allowed region with the best fit of $|\Delta m_{41}^2|=2.41\,\pm\,0.03\,$\,eV$^2$ and $\sin^2 2\theta_{14}$=0.08$\,\pm\,$0.03 with a p-value of 8.2\%. Comparisons of obtained reactor antineutrino spectra at reactor sources are made among RENO, NEOS, and Daya Bay to find a possible spectral variation.Comment: 6 pages, 5 figures: This manuscript has been significantly revised by the joint reanalysis by RENO and NEOS Collaborations. (In the previous edition, the RENO collaboration used publicly available NEOS data to evaluate the expected neutrino spectrum at NEOS.

Detection of Antineutrinos for Reactor Monitoring

Reactor neutrinos have been detected in the past 50 years by various detectors for different purposes. Beginning in the 1980s, neutrino physicists have tried to use neutrinos to monitor reactors and develop an optimized detector for nuclear safeguards. Recently, motivated by neutrino oscillation physics, the technology and scale of reactor neutrino detection have progressed considerably. In this review, I will give an overview of the detection technology for reactor neutrinos, and describe the issues related to further improvements in optimized detectors for reactor monitoring. © 2016 Published by Elsevier Korea LLC on behalf of Korean Nuclear Society1111sciescopuskc

Recent Results of COSINE-100 Experiment and Future Plan

COSINE-100 is an experiment to test the long standing claim of dark matter modulation signals from DAMA/LIBRA group. We have developed the same type of crystals as DAMA/LIBRA experiment, low background NaI(Tl) crystal detectors using high quantum efficiency PMTs with a total mass of about 100 kg. The detectors were immersed in liquid scintillator of 2 tons to remove K-40 backgrounds around 3 keV and muon veto scintillators were surrounding the heavy shielding made by lead. The COSINE-100 detectors were installed at the 700 meter deep underground laboratory, Y2L in Korea and we have been taking data continuously from September of 2016, more than 2.5 years. We observed no excess of events over the simulated backgrounds of known sources in an early part of the data, with which we could rule out the&nbsp; interpretation of DAMA/LIBRA data as WIMP-nucleon spin-independent interaction assuming the standard halo model. Further analysis results for annual modulation in COSINE-100 data for 1.7 years will be compared with DAMA/LIBRA and a recent ANAIS experiment. I will try to describe the future experimental plans of COSINE collaboration for the complete validation of the DAMA/LIBRA experiment too.</p

Detection of Antineutrinos for Reactor Monitoring

Reactor neutrinos have been detected in the past 50 years by various detectors for different purposes. Beginning in the 1980s, neutrino physicists have tried to use neutrinos to monitor reactors and develop an optimized detector for nuclear safeguards. Recently, motivated by neutrino oscillation physics, the technology and scale of reactor neutrino detection have progressed considerably. In this review, I will give an overview of the detection technology for reactor neutrinos, and describe the issues related to further improvements in optimized detectors for reactor monitoring

Growth and characterization of Na2Mo2O7 crystal scintillators for rare event searches

Disodium dimolybdate (Na2Mo2O7) crystals were grown using the Czochralski technique. The thermal characteristics of the compound were analyzed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements. The crystal structure of the grown sample was confirmed using X-ray diffraction (XRD). Luminescence properties were measured at room and low temperatures, using a light emitting diode (LED) source. Very weak luminescence was observed at room temperature; however, the luminescence intensity was enhanced at low temperatures. The crystal&apos;s transmittance spectrum was measured for estimating its optical quality and energy band gap. The grown crystal exhibited a luminescence light yield of 55% compared with CaMoO4 crystals at 10 K, when excited by a 280-nm-wavelength LED source, but does not have the drawbacks of radioactive Ca isotopes. These results suggest that at cryogenic temperatures, Na2Mo2O7 crystal scintillators are promising for the detection of dark matter and neutrinoless double beta decay of Mo-100. (C) 2017 Elsevier B.V. All rights reserved1111sciescopu