Measurement of the Background Activities of a 100Mo-enriched Powder Sample for an AMoRE Crystal Material by Using a Single High-Purity Germanium Detector

Park Su-yeon,Hahn Insik,Kang Woon Gu,Kim Gowoon,Lee Eunkyung,Leonard Douglas S.,Kazalov Vladimir,Kim Yeong Duk,LEEMOOHYUN,Sala Elena 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.12

The Advanced Molybdenum-based Rare process Experiment (AMoRE) searches for neutrino-less double-beta (0νββ) decay of 100Mo in enriched molybdate crystals. The AMoRE crystals must have low levels of radioactive contamination to achieve low background signals with energies near the Q-value of the 100Mo 0νββ decay. To produce low-activity crystals, radioactive contaminants in the raw materials used to form the crystals must be controlled and quantified. 100EnrMoO3 powder, which is enriched in the 100Mo isotope, is of particular interest as it is the source of 100Mo in the crystals. A high-purity germanium detector having 100% relative efficiency, named CC1, is being operated in the Yangyang underground laboratory. Using CC1, we collected a gamma spectrum from a 1.6-kg 100EnrMoO3 powder sample enriched to 96.4% in 100Mo. Activities were analyzed for the isotopes 228Ac, 228Th, 226Ra, and 40K. They are long-lived naturally occurring isotopes that can produce background signals in the region of interest for AMoRE. Activities of both 228Ac and 228Th were < 1.0 mBq/kg at 90% confidence level (C.L.). The activity of 226Ra was measured to be 5.1 ± 0.4 (stat) ± 2.2 (syst) mBq/kg. The 40K activity was found as < 16.4 mBq/kg at 90% C.L.

Determination of Mo- and Ca-isotope ratios in ^{Ca 100} _{MoO 4} crystal for AMoRE-I experiment

Karki, S.,Aryal, P.,Kim, H.J.,Kim, Y.D.,Park, H.K. Elsevier 2018 Nuclear Instruments & Methods in Physics Research. Vol.877 No.-

<P><B>Abstract</B></P> <P>The first phase of the AMoRE (Advanced Mo-based Rare process Experiment) is to search for neutrinoless double-beta decay of <SUP>100</SUP>Mo with calcium molybdate ( <SUP> Ca 100 </SUP> <SUB> MoO 4 </SUB> ) crystals enriched in <SUP>100</SUP>Mo and depleted in <SUP>48</SUP>Ca using a cryogenic technique at Yangyang underground laboratory in Korea. It is important to know <SUP>100</SUP>Mo- and <SUP>48</SUP>Ca-isotope ratios in <SUP> Ca 100 </SUP> <SUB> MoO 4 </SUB> crystal to estimate half-life of <SUP>100</SUP>Mo decays and to 2 ν β β background from <SUP>48</SUP>Ca. We employed the ICP-MS (Inductive Coupled Plasma Mass Spectrometer) to measure <SUP>100</SUP>Mo- and <SUP>48</SUP>Ca-isotope ratios in <SUP> Ca 100 </SUP> <SUB> MoO 4 </SUB> crystal. The measured results for <SUP>100</SUP>Mo- and <SUP>48</SUP>Ca-isotope ratios in the crystal are ( 94 . 6 ± 2 . 8 ) % and ( 0 . 00211 ± 0 . 00006 ) %, respectively, where errors are included both statistical and systematic uncertainties.</P>

Light sterile neutrino and leptogenesis

Jung Ki-Young,Siyeon Kim 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.12

We studied models of leptogenesis where three right-handed Majorana neutrinos are involved and the minimal-extended seesaw mechanism including an additional singlet feld produces four light neutrinos. This study shows that the type of mass ordering and heavy Majorana scales can be determined by inputting the simplest orthogonal matrix into the Casas-Ibarra (CI) representation of seesaw. The CP asymmetry produced from the decays of heavy neutrinos and the dilution mass are predicted in terms of the mass and mixing elements of the fourth neutrino. Upon the choice of CI matrix, the existence of a light sterile neutrino is required to explain the high-energy lepton asymmetry in light of phenomenological measurements. Although there are several free parameters attributable to an additional neutrino, the model can be in part constrained by low-energy experiments such as sterile neutrino searches and neutrinoless double-beta decays, as well as the observed baryon asymmetry in the universe.

Neutrinoless Double Beta Decay and Light Sterile Neutrino

C. H. Jang,B. J. Kim,Y. J. Ko,K. Siyeon 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.11

The recent neutrino experiment results show a preference on normal mass ordering of neutrinos. The global efforts to search for neutrinoless double beta decays undergo a broad gap with the approach to the prediction in three-neutrino framework based on the normal ordering. Current research is to show that it is possible to find a neutrinoless double beta decay signal even with normal ordered neutrino masses. We propose the existence of light sterile neutrino as a solution to the higher effective mass of electron neutrino expected by experiments under operation. A few short-baseline oscillation experiments gave rise to exclusion bound to the mass of sterile neutrino and its mixing with the lightest neutrino. It is demonstrated that results of neutrinoless double beta decays can also narrow down the ranges of the mass and the mixing angle of sterile neutrino.

The development of a cryogenic detector with CaMoO₄ crystals for neutrinoless double beta decay search

Lee, S.J.,Choi, J.H.,Danevich, F.A.,Jang, Y.S.,Kang, W.G.,Khanbekov, N.,Kim, H.J.,Kim, I.H.,Kim, S.C.,Kim, S.K.,Kim, Y.D.,Kim, Y.H.,Kobychev, V.V.,Kornoukhov, V.N.,Lee, J.I.,Lee, J.S.,Lee, K.B.,Lee, M North-Holland ; Elsevier Science Ltd 2011 Astroparticle physics Vol.34 No.9

The search for neutrinoless double beta decay (0νββ) is a key experiment for evaluating the mass of the neutrino and for determining the Majorana/Dirac nature of neutrinos. A scintillating CaMoO<SUB>4</SUB> crystal is a good material for use in investigating 0νββ with cryogenic detectors. The high transition energy (Q=3034keV) and nearly 10% natural abundance of <SUP>100</SUP>Mo, together with the scintillating property of the crystal, provide favorable conditions to search for 0νββ of <SUP>100</SUP>Mo. We report a prototype experiment operating at low temperatures using a CaMoO<SUB>4</SUB> crystal as a particle absorber. Prior to testing of isotopically-enriched <SUP>40</SUP>Ca<SUP>100</SUP>MoO<SUB>4</SUB> crystals, a CaMoO<SUB>4</SUB> crystal with Mo of natural isotopic composition was tested. Using a metallic magnetic calorimeter as a temperature sensor, we achieved high energy resolutions for alpha particles and low-energy gamma rays. This experiment shows the feasibility of scaling up the crystal size to perform a high sensitivity search for 0νββ decay of <SUP>100</SUP>Mo.

Ultra-low gamma-ray measurement system for neutrinoless double beta decay

Kang, W.G.,Choi, J.H.,Jeon, E.J.,Lee, J.I.,Kim, H.J.,Kim, S.K.,Kim, Y.D.,Lee, J.H.,Ma, K.J.,Myung, S.S.,So, J.H. Pergamon Press ; Elsevier Science Ltd 2013 Applied radiation and isotopes Vol.81 No.-

An experiment for the detection of 0νβ<SUP>+</SUP>/EC and 0νEC/EC in 92Mo nuclei has been carried out with a scintillating crystal, CaMoO<SUB>4</SUB>, in coincidence with the HPGe detector. We study the background events inside the event selection window for 0ν β<SUP>+</SUP>/EC decays of CaMoO<SUB>4</SUB> detector. For 51.2 days of data taking period, we didn't observe any event in the neutrinoless EC/EC decay event window. The <SUP>92</SUP>Mo 0νβ<SUP>+</SUP>/EC decay half-life limit was set to 0.61x10<SUP>20</SUP> years with a 90% confidence by method of Feldman and Cousins. This ultra-low gamma ray measurement utilizing coincidence technique can be used for the resonant EC/EC decay process of some nuclei which is potentially important for neutrinoless double beta decay process.

Luminescence and scintillation characterization of PbMoO₄ crystal for neutrinoless double beta decay search

Khan, Arshad,Daniel, D. Joseph,Kim, Hongjoo,Pandey, Indra Raj,Shlegel, Vladimir,Lee, Moo Hyun,Kim, Yeongduk Elsevier 2019 Radiation measurements Vol.123 No.-

<P><B>Abstract</B></P> <P>A PbMoO<SUB>4</SUB> single crystal with optically good quality and crack free, bulk crystal is grown by the low thermal gradient Czochralski method. The luminescence and scintillation properties of the grown crystal are measured under the excitations by 4.4 eV UV, 662 keV γ, 5.5 MeV α, and β in the temperature range of 10–300 K. The light yield under UV and β excitations are found to enhance down to 10 K, however quenched below 50 K under γ and α excitations. The major luminescence and scintillation decay time constants are found to be 20 μs, 18 μs, and 28 μs, respectively, with 4.4 eV, 662 keV γ, and 5.5 MeV α excitations at 10 K. The thermally stimulated luminescence (TSL) glow curve measured after X-ray irradiation at 10 K, shows three overlapping peaks in the temperature range of 10–70 K. The TSL kinetic parameters such as trap depth (E) and frequency factor (s) are determined by using general order kinetics and found to be, 41.5 K (peak-1), 35 meV, 3.95 × 10<SUP>2</SUP> s<SUP>−1</SUP>, 51.1 K (peak-2), 121 meV, 4.31 × 10<SUP>10</SUP> s<SUP>−1</SUP>, and 56.8 K (peak-3), 123 meV, 3.32 × 10<SUP>9</SUP> s<SUP>−1</SUP>. The quenching of scintillation light yield under α and γ excitations at lower temperature is due to the self-trapping of electrons at (MoO<SUB>4</SUB>)<SUP>2-</SUP> molecular complex.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Luminescence, scintillation and TSL properties are studied in 10–300 K range. </LI> <LI> Scintillation light under α- and γ-rays excitation quenches below 50 K. </LI> <LI> Light yield enhances under UV and β-rays excitation down to 10 K. </LI> <LI> The major decay time becomes slower with decreasing the temperature. </LI> <LI> TSL kinetics parameters are calculated with general order kinetics. </LI> </UL> </P>

Neutrino mass matrix in triplet Higgs models with _A4 symmetry

Oh, Myoung Chu,Baek, Seungwon Elsevier 2010 Physics letters: B Vol.690 No.1

<P><B>Abstract</B></P><P>We consider triplet Higgs model with <SUB>A4</SUB> symmetry to generate the neutrino mass matrix. The tribimaximal form of the neutrino mixing matrix can be naturally obtained. Imposing the neutrino oscillation data, we show that 1) both normal and inverted mass hierarchy are allowed, 2) there is a lower bound on the lightest neutrino mass and the effective mass for neutrinoless double beta decay, 3) the non-vanishing <SUB>θ13</SUB> can be accommodated by considering small perturbation, 4) <SUB>θatm</SUB> should be very close to π/4 even after perturbation.</P>

Simulations of background sources in AMoRE-I experiment

Luqman, A.,Ha, D.H.,Lee, J.J.,Jeon, E.J.,Jo, H.S.,Kim, H.J.,Kim, Y.D.,Kim, Y.H.,Kobychev, V.V.,Lee, H.S.,Park, H.K.,Siyeon, K.,So, J.H.,Tretyak, V.I.,Yoon, Y.S. Elsevier 2017 Nuclear instruments & methods in physics research. Vol.855 No.-

<P><B>Abstract</B></P> <P>The first phase of the Advanced Mo-based Rare process Experiment (AMoRE-I), an experimental search for neutrinoless double beta decay ( 0 ν β β ) of <SUP>100</SUP>Mo in calcium molybdate ( <SUP> 40 </SUP> Ca<SUP>100</SUP>MoO<SUB>4</SUB>) crystal using cryogenic detection techniques, is in preparation at the YangYang underground laboratory (Y2L) in Korea. A GEANT4 based Monte Carlo simulation was performed for the first-phase AMoRE detector and shield configuration. Background sources such as <SUP>238</SUP>U, <SUP>232</SUP>Th, <SUP>235</SUP>U, and <SUP>210</SUP>Pb from inside the crystals, surrounding materials, outer shielding walls of the Y2L cavity were simulated. The estimated background rate in the region of interest was estimated to be < 1.5 × <SUP> 10 − 3 </SUP> counts/keV/kg/yr (ckky). The effects of random coincidences between backgrounds and two-neutrino double beta decays of <SUP>100</SUP>Mo as a potential background source were estimated to be < 2.3 × <SUP> 10 − 4 </SUP> ckky.</P>

A Convenient Approach to 10−12 g/g ICP-MS Limits for Th and U in Aurubis Electrolytic NA-ESN Brand Copper

Douglas S. Leonard 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.12

Inductively-coupled-plasma mass spectroscopy is a powerful technique for measuring trace levelsof radioactive contaminants, specifically Th and U, in materials for use in construction of lowbackgroundrare-event detectors such as double beta decay and dark matter detectors. I describehere a technique for measuring Th and U contamination in copper by using direct acid digestionand dilution without further chemical processing, achieving results comparable to those achievedin previous work [1, 2] which utilized more complex chemical pre-concentration techniques. Aconvenient research-oriented analysis environment is described as well. Results are presented formeasurements of three samples from the production line of electrolytically-purified, LME (LondonMetal Exchange) grade A, NA-ESN Aurubis copper. Purified samples showed levels consistent withzero contamination for both elements, while weak, but inconclusive, indications of contaminationwere present for the unpurified anode copper. The best limits achieved are near 1·10−12 g/g (95%CL) for both Th and U measured for copper from the cathode of the purification process.