33 research outputs found

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

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    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

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

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    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

    Pulse-shape discrimination between electron and nuclear recoils in a NaI(Tl) crystal

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    Abstract: We report on the response of a high light-output NaI(Tl) crystal to nuclear recoils induced by neutrons from an Am-Be source and compare the results with the response to electron recoils produced by Compton-scattered 662 keV γ-rays from a 137Cs source. The measured pulse-shape discrimination (PSD) power of the NaI(Tl) crystal is found to be significantly improved because of the high light output of the NaI(Tl) detector. We quantify the PSD power with a quality factor and estimate the sensitivity to the interaction rate for weakly interacting massive particles (WIMPs) with nucleons, and the result is compared with the annual modulation amplitude observed by the DAMA/LIBRA experiment. The sensitivity to spin-independent WIMP-nucleon interactions based on 100 kg·year of data from NaI detectors is estimated with simulated experiments, using the standard halo model. © 2015, The Author(s)1371Nsciescopu

    GEANT4 Simulation of the Shielding of Neutrons from Cf-252 Source

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    We have done simulation studies of the neutron shielding for a Cf-252 source using GEANT4. For the energy distribution of the neutrons emitted from Cf-252, we have assumed the Watt fission spectrum. The neutron absorption dose rates with and without the shield are estimated for three different materials of Type 304 SS, NS-4-FR and Resin-F. Among various physics models of GEANT4 for the hadronic interactions of low-energy neutrons, we have used the High Precision (HP) model, which is based on the ENDF-VI data and is able to treat elastic, inelastic, fusion and fission processes for neutrons. We have investigated the accuracy of this HP model of GEANT4 by comparing the simulation results with those from MCNP5 and experimental data11Nsciescopuskc

    Simulations of therapeutic proton beam formation with GEANT4

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    The proton beam formation for therapy has been studied with Monte Carlo simulations. This numerical study was performed in conjunction with the measurements made in the horizontal beam line of the Midwest Proton Radiotherapy Institute (MPRI) in the USA. The simulations included necessary beam-modifying devices of the beam line, and were compared to the dose distributions measured in water and in air using an ionization chamber. Therapeutic beams were produced using a double-scattering method in the transverse planes and using a rotating modulator in the beam direction. The results showed that important physical parameters of a therapy beam such as lateral penumbra and source to axis distance (SAD) can be simulated to agree with experimental values within 5 %11Nsciescopuskc

    KoBRA Wien filter for low-energy RI beam production and recoil separation

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    The Wien filter is one of the key components in ion optics to improve the mass separation performance. The KoBRA Wien filter will be installed at the low-energy beamline KoBRA of RAON in Korea. The specifications of the KoBRA Wien filter were determined based on the ion beams expected in the KoBRA beamline, especially, beam energies less than about 5 MeV/nucleon suitable for nuclear astrophysics experiments. The Wien filter is designed to have the maximum field intensities of 0.2 T for the magnetic field and 2.0 kV/mm for the electric field in the ±75(H)×±50(V)×2500(L)mm3 good-field region. Performance of the Wien filter was estimated by the ion optics calculations of the KoBRA beamline for 40Ar beams at 18.5 MeV/nucleon and 14O beams at 2.5 MeV/nucleon. The mass resolving powers are 42.65 and 517, respectively. Currently, the KoBRA Wien filter is being manufactured, and will perform a factory acceptance test. © 2023 Elsevier B.V.11Nsciescopu

    New fast-timing γ-ray detection system in Korea: KHALA

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    KHALA, the acronym for Korea high-resolution array of LaBr3(Ce), has been developed to measure the lifetimes of the nuclear excited states. This system consists of 36 cylindrical LaBr3(Ce) scintillator crystals with a diameter and length of 1.5 inches each. It is suitable for measuring γ-ray emission time from a few tens of picoseconds to a few tens of nanoseconds. The data acquisition electronics of KHALA are fully digitized for both energy and timing information, resulting in the quick data processing. Detailed performance specifications, such as the energy resolution, timing response, and photopeak detection efficiency, of KHALA are presented. © 2023 Elsevier B.V.11Nsciescopu

    Improved intensities for the gamma transitions with E-gamma > 3 MeV from Pb-208

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    Pb-208 is a doubly magic nucleus which has been studied extensively by many experiments and nuclear models. Its properties, such as excitation energies, spins, and parities of the ground and excited states are well known. However, some gamma transitions with E-gamma > 3 MeV from the excited states to the ground state in Pb-208 have never been observed. The intensities of these gamma transitions are important issues for 0 nu beta beta decay searches because these transitions can make non-negligible background signals depending on their intensities. We conducted a measurement to search for the 3197.7, 3475.1, and 3708.4 keV transitions, which are emitted from the second, third, and fourth excited states in Pb-208, respectively. A 2 kg ThO2 sample was measured using a 100% relative efficiency high-purity germanium detector for 39.5 days at Y2L, an underground laboratory in Yangyang, Korea. We improved upper limits for intensities of the 3197.7, 3475.1, and 3708.4 keV gamma transitions as <1.2 x 10(-4)%, <1.4 x 10(-4)%, and <1.2 x 10(-4)%, respectively. These upper limits are at least a factor of 19 better than the previous results.11Nsciescopu

    Development of an array of fourteen HPGe detectors having 70% relative efficiency each

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    Searches for new physics push experiments to look for increasingly rare interactions. As a result, detectors require increasing sensitivity and specificity, and materials must be screened for naturally occurring, background-producing radioactivity. Furthermore, the detectors used for screening must approach the sensitivities of the physics-search detectors themselves, thus motivating iterative development of detectors capable of both physics searches and background screening. We report on the design, installation, and performance of a novel, low-background, fourteen-element high-purity germanium detector named the CAGe (CUP Array of Germanium), installed at the Yangyang underground laboratory in Korea.11Nsciescopu

    Study on the application of SiPM to γ ray and charged particle measurement using scintillation crystals

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    The characteristics of a Silicon Photo Multiplier (SiPM)-based scintillation detector system were studied. The influence of the bias voltage and the number of SiPMs on the energy resolution was identified. The single SiPM energy spectra in the multi-SiPM system showed their dependency on the position of the 60Co radiation source. The application of geometric mean on the multi-SiPM system was also considered to bypass single channel calibrations. Preliminary results on the performances of developing scintillation detectors with a CsI(Tl) crystal or a plastic scintillator are demonstrated. The capability of charged particle measurement for CsI(Tl) crystal and sub-nanosecond timing resolution of plastic scintillator were identified. © 2023 Elsevier B.V.11Nsciescopu
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