Measurement of the Background Activities of a 100Mo-enriched powder sample for AMoRE crystal material using a single high purity germanium detector

The Advanced Molybdenum-based Rare process Experiment (AMoRE) searches for neutrino-less double-beta (0{\nu}\b{eta}\b{eta}) 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 0{\nu}\b{eta}\b{eta} 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 \pm 0.4 (stat) \pm 2.2 (syst) mBq/kg. The 40K activity was found as < 16.4 mBq/kg at 90% C.L.Comment: 20 pages, 6 figures, 5 table

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

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

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

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

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

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

Measurements of the Specific Activities of 137Cs in Antarctica Environmental Samples by Using the Low-Level Radiation Analysis Method

© 2020, The Korean Physical Society. Since the King Sejong Korean Antarctic Research Station began operation in 1988, studies of various fields have been then carried out in polar regions and significant achievements have been yielded. However, environmental and biological radiations have not been dealt with compared to other research areas. In this study, the 137Cs distribution is investigated for environmental elements in the vicinity of the two research stations, the Jang Bogo Station and the King Sejong Station, operated by the Korea Polar Research Institute (KOPRI) in Antarctica by using a low-level radiation analysis method. Three different types of environmental samples, soils, mosses, and lichens are investigated for identification of 137Cs. In order to discriminate low levels of radiations from background radiations and estimate their specific activities with high reliability and precision, we used a heavily shielded HPGe detector in an underground laboratory to perform the activity measurements. GEANT4 simulations were carried out for efficiency calibrations corresponding to the shape of the pre-processed sample. 137Cs has been identified in all the samples and the energy spectrum has been found to reflect their physical and ecological characteristics11sciekc

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

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