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1.
Phys Rev Lett ; 131(20): 201802, 2023 Nov 17.
Artigo em Inglês | MEDLINE | ID: mdl-38039466

RESUMO

We search for energetic electron recoil signals induced by boosted dark matter (BDM) from the galactic center using the COSINE-100 array of NaI(Tl) crystal detectors at the Yangyang Underground Laboratory. The signal would be an excess of events with energies above 4 MeV over the well-understood background. Because no excess of events are observed in a 97.7 kg·yr exposure, we set limits on BDM interactions under a variety of hypotheses. Notably, we explored the dark photon parameter space, leading to competitive limits compared to direct dark photon search experiments, particularly for dark photon masses below 4 MeV and considering the invisible decay mode. Furthermore, by comparing our results with a previous BDM search conducted by the Super-Kamionkande experiment, we found that the COSINE-100 detector has advantages in searching for low-mass dark matter. This analysis demonstrates the potential of the COSINE-100 detector to search for MeV electron recoil signals produced by the dark sector particle interactions.

2.
Phys Rev Lett ; 122(13): 131802, 2019 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-31012610

RESUMO

A search for inelastic boosted dark matter (IBDM) using the COSINE-100 detector with 59.5 days of data is presented. This relativistic dark matter is theorized to interact with the target material through inelastic scattering with electrons, creating a heavier state that subsequently produces standard model particles, such as an electron-positron pair. In this study, we search for this electron-positron pair in coincidence with the initially scattered electron as a signature for an IBDM interaction. No excess over the predicted background event rate is observed. Therefore, we present limits on IBDM interactions under various hypotheses, one of which allows us to explore an area of the dark photon parameter space that has not yet been covered by other experiments. This is the first experimental search for IBDM using a terrestrial detector.

3.
Phys Rev Lett ; 123(3): 031302, 2019 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-31386435

RESUMO

We present new constraints on the dark matter-induced annual modulation signal using 1.7 years of COSINE-100 data with a total exposure of 97.7 kg yr. The COSINE-100 experiment, consisting of 106 kg of NaI(Tl) target material, is designed to carry out a model-independent test of DAMA/LIBRA's claim of WIMP discovery by searching for the same annual modulation signal using the same NaI(Tl) target. The crystal data show a 2.7 cpd/kg/keV background rate on average in the 2-6 keV energy region of interest. Using a χ-squared minimization method we observe best fit values for modulation amplitude and phase of 0.0092±0.0067 cpd/kg/keV and 127.2±45.9 d, respectively.

4.
J Xray Sci Technol ; 25(3): 505-514, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28157115

RESUMO

The King AbdulAziz City for Science & Technology in the Kingdom of Saudi Arabia plans to build a 10 MeV, 15 kW linear accelerator (LINAC) for electron beam and X-ray. The accelerator will be supplied by EB Tech, Republic of Korea, and the design and construction of the accelerator building will be conducted in the cooperation with EB Tech. This report presents the shielding analysis of the accelerator building using the Monte Carlo N-Particle Transport Code (MCNP). In order to improve the accuracy in estimating deep radiation penetration and to reduce computation time, various variance reduction techniques, including the weight window (WW) method, the deterministic transport (DXTRAN) spheres were considered. Radiation levels were estimated at selected locations in the shielding facility running MCNP6 for particle histories up to 1.0×10+8. The final results indicated that the calculated doses at all selected detector locations met the dose requirement of 50 mSv/yr, which is the United State Nuclear Regulatory Commission (U.S. NRC) requirement.


Assuntos
Aceleradores de Partículas , Proteção Radiológica , Elétrons , Desenho de Equipamento , Método de Monte Carlo , Proteção Radiológica/instrumentação , Proteção Radiológica/métodos , Raios X
5.
Appl Radiat Isot ; 193: 110654, 2023 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-36646029

RESUMO

The CUP array of germanium (CAGe) is an array of fourteen high-purity germanium (HPGe) detectors. The detection efficiency of full-energy-peak emitted from the various samples assayed on the CAGe was calculated using the Monte Carlo simulation toolkit GEANT4. If the dead layer on the surface of the crystal is treated in the simulation as a continuous part of the active crystal, then the detection efficiency will be overestimated. Thus, the detection efficiency of the CAGe was adjusted using multi-nuclide source data and Monte Carlo simulations. The gamma spectra of the known activity source were obtained for each HPGe detector of the CAGe. The detection efficiency measured by the multi-source data was smaller than that of simulation data if the simulation treated the whole volume of germanium crystals as active for gamma detection. By optimizing the dead layers' thicknesses in the simulation, the detection efficiency calculated by the simulation could be matched to that of multi-source data.

6.
Phys Rev Lett ; 108(18): 181301, 2012 May 04.
Artigo em Inglês | MEDLINE | ID: mdl-22681055

RESUMO

New limits are presented on the cross section for weakly interacting massive particle (WIMP) nucleon scattering in the KIMS CsI(Tℓ) detector array at the Yangyang Underground Laboratory. The exposure used for these results is 24 524.3 kg·days. Nuclei recoiling from WIMP interactions are identified by a pulse shape discrimination method. A low energy background due to alpha emitters on the crystal surfaces is identified and taken into account in the analysis. The detected numbers of nuclear recoils are consistent with zero and 90% confidence level upper limits on the WIMP interaction rates are set for electron equivalent energies from 3 to 11 keV. The 90% upper limit of the nuclear recoil event rate for 3.6-5.8 keV corresponding to 2-4 keV in NaI(Tℓ) is 0.0098 counts/kg/keV/day, which is below the annual modulation amplitude reported by DAMA. This is incompatible with interpretations that enhance the modulation amplitude such as inelastic dark matter models. We establish the most stringent cross section limits on spin-dependent WIMP-proton elastic scattering for the WIMP masses greater than 20 GeV/c2.

7.
Eur Phys J C Part Fields ; 78(6): 490, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30956554

RESUMO

The COSINE-100 dark matter search experiment is an array of NaI(Tl) crystal detectors located in the Yangyang Underground Laboratory (Y2L). To understand measured backgrounds in the NaI(Tl) crystals we have performed Monte Carlo simulations using the Geant4 toolkit and developed background models for each crystal that consider contributions from both internal and external sources, including cosmogenic nuclides. The background models are based on comparisons of measurement data with Monte Carlo simulations that are guided by a campaign of material assays and are used to evaluate backgrounds and identify their sources. The average background level for the six crystals (70 kg total mass) that are studied is 3.5 counts/day/keV/kg in the (2-6) keV energy interval. The dominant contributors in this energy region are found to be 210 Pb and 3 H.

8.
Appl Radiat Isot ; 81: 290-3, 2013 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-23726518

RESUMO

An experiment for the detection of 0νß(+)/EC and 0νEC/EC in 92Mo nuclei has been carried out with a scintillating crystal, CaMoO4, in coincidence with the HPGe detector. We study the background events inside the event selection window for 0ν ß(+)/EC decays of CaMoO4 detector. For 51.2 days of data taking period, we didn't observe any event in the neutrinoless EC/EC decay event window. The (92)Mo 0νß(+)/EC decay half-life limit was set to 0.61×10(20) 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.


Assuntos
Raios gama , Isótopos/análise , Molibdênio/análise , Contagem de Cintilação/instrumentação , Espectrometria gama/instrumentação , Partículas beta , Partículas Elementares , Desenho de Equipamento , Análise de Falha de Equipamento , Meia-Vida , Doses de Radiação , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
9.
Appl Radiat Isot ; 69(9): 1294-8, 2011 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-21592803

RESUMO

We investigate the caesium concentrations in soils in mountain areas near Gori nuclear power plant in Korea, focusing on the measurement limits to the (134)Cs. In order to lower the minimum detectable amount (MDA) of activity for the (134)Cs, we have used the ammonium molybdophosphate (AMP) precipitation method to get rid of the (40)K existing in natural radioactivity, which reduces the MDA activity about 10 times smaller than those without the AMP precipitation method. The MDA results for the (134)Cs were found to be in the range between 0.015 and 0.044 Bq/kg-dry weight. In order to diminish the background, we also have measured a part of the soil samples in Yangyang, a small town in the east coast of Korea. However, it turns out that in order to detect the (134)Cs in the samples the MDA should be reduced to the level of mBq/kg-dry weight.


Assuntos
Radioisótopos de Césio/análise , Poluentes Radioativos do Solo/análise , Precipitação Química , Monitoramento Ambiental , Coreia (Geográfico) , Limite de Detecção , Molibdênio/química , Ácidos Fosfóricos/química , Solo/química
10.
Phys Rev Lett ; 99(9): 091301, 2007 Aug 31.
Artigo em Inglês | MEDLINE | ID: mdl-17930998

RESUMO

The Korea Invisible Mass Search (KIMS) experiment presents new limits on the weakly interacting massive particle (WIMP)-nucleon cross section using data from an exposure of 3409 kg.d taken with low-background CsI(Tl) crystals at the Yangyang Underground Laboratory. The most stringent limit on the spin-dependent interaction for a pure proton case is obtained. The DAMA signal region for both spin-independent and spin-dependent interactions for the WIMP masses greater than 20 GeV/c2 is excluded by the single experiment with crystal scintillators.

11.
Acta Microbiol Hung ; 36(1): 67-75, 1989.
Artigo em Inglês | MEDLINE | ID: mdl-2603646

RESUMO

The prototype strain of the human adenovirus type 35 (AV35) was examined. BamHI, EcoRI, HindIII, KpnI, PstI, and SalI restriction endonucleases were used for the mapping of DNA fragments. Three original maps were constructed, and previously published maps were somewhat modified. A PstI-specific fragment library was also prepared and characterized using the pBR322/E. coli system. Some of the recombinants seem to be applicable for rapid DNA diagnostics, and for the comparative mapping of type- and subgroup-specific DNA sequences. The comparative presentation of physical maps of subgroup B human adenoviruses might improve the efficiency of genotyping of adenoviruses using restriction endonucleases.


Assuntos
Adenovírus Humanos/genética , DNA Viral/genética , Clonagem Molecular , Sondas de DNA , Desoxirribonucleases de Sítio Específico do Tipo II , Mapeamento por Restrição
12.
Acta Microbiol Hung ; 36(4): 445-57, 1989.
Artigo em Inglês | MEDLINE | ID: mdl-2534900

RESUMO

Cloned PstI fragments of human adenovirus 35 (AV35) genome were compared with the DNA of representatives of human adenovirus subgroups A (type 12), B (type 7), C (types 1, and 5), D (type 8), and E (type 4), using blot hybridization techniques. The E1b region of AV35 was found to be more distantly related to those of other subgroups than E1a regions sequences and examined by others. DNA hybridization was observed only between E1b of AV35 and the DNA of AV4, thus the recombinant constructed might be applied as B-subgroup-specific diagnostic probe. Common nucleotide sequences were detected within the E3 regions of serotypes 1, 4, 5, 7, 8, and 35. On the basis of inter-subgroup homology, and PstI-fragments it may be concluded, that the structure of E3 sequences of AV7 and AV35 DNA are closely related to those of AV3 DNA sequenced by Signäs et al. [18]. E4 regions were compared only of serotypes representing subgroups B, C, and D. These sequences were subgroup specific, similarly to E1b regions.


Assuntos
Adenovírus Humanos/genética , DNA Viral , Proteínas de Ligação a DNA/genética , Proteínas Oncogênicas Virais/genética , Proteínas Precoces de Adenovirus , Infecções por Adenovirus Humanos/complicações , Infecções por Adenovirus Humanos/genética , Southern Blotting , Células Cultivadas , Humanos , Síndromes de Imunodeficiência/complicações , Síndromes de Imunodeficiência/genética , Síndromes de Imunodeficiência/microbiologia , Prevalência , Homologia de Sequência do Ácido Nucleico
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