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Search Results: 1 - 10 of 130401 matches for " V. Kobychev "
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Constraints on the photon charge based on observations of extragalactic sources
V. V. Kobychev,S. B. Popov
Physics , 2004, DOI: 10.1134/1.1883345
Abstract: Using modern high-resolution observations of extragalactic compact radio sources we obtain an estimate of the upper bound on a photon electric charge at the level $e_{\gamma} \lesssim 3 \cdot 10^{-33}$ of elementary charge (assuming the photon charge to be energy independent). This is three orders of magnitude better than the limit obtained with radio pulsar timing. Also we set a limit on a photon charge in the gamma-ray band (energies about 0.1 MeV). In future the estimate made for extragalactic sources can be significantly improved.
Optimization of light collection from crystal scintillators for cryogenic experiments
F. A. Danevich,R. V. Kobychev,V. V. Kobychev,H. Kraus,V. B. Mikhailik,V. M. Mokina
Physics , 2014, DOI: 10.1016/j.nima.2014.01.042
Abstract: High light collection efficiency is an important requirement in any application of scintillation detectors. The purpose of this study is to investigate the possibility for improving this parameter in cryogenic scintillation bolometers, which can be considered as a promising detectors in experiments investigating neutrinoless double beta decay and dark matter. Energy resolutions and relative pulse amplitudes of scintillation detectors using ZnWO4 scintillation crystals of different shapes (cylinder 20 mm in dimater by 20 mm and hexagonal prism with diagonal 20 mm and height 20 mm), reflector materials and shapes, optical contact and surface properties (polished and diffused) were measured at room temperature. Propagation of optical photons in these experimental conditions was simulated using Geant4 and ZEMAX codes. The results of the simulations are found to be in good agreement with each other and with direct measurements of the crystals. This could be applied to optimize the geometry of scintillation detectors used in the cryogenic experiments.
Impact of geometry on light collection efficiency of scintillation detectors for cryogenic rare event searches
F. A. Danevich,V. V. Kobychev,R. V. Kobychev,H. Kraus,V. B. Mikhailik,V. M. Mokina,I. M. Solsky
Physics , 2014, DOI: 10.1016/j.nimb.2014.06.015
Abstract: Simulations of photon propagation in scintillation detectors were performed with the aim to find the optimal scintillator geometry, surface treatment, and shape of external reflector in order to achieve maximum light collection efficiency for detector configurations that avoid direct optical coupling, a situation that is commonly found in cryogenic scintillating bolometers in experimental searches for double beta decay and dark matter. To evaluate the light collection efficiency of various geometrical configurations we used the ZEMAX ray-tracing software. It was found that scintillators in the shape of a triangular prism with an external mirror shaped as truncated cone gives the highest light collection efficiency. The results of the simulations were confirmed by carrying out measurements of the light collection efficiencies of CaWO4 crystal scintillators. A comparison of simulated and measured values of light output shows good agreement
Heat flow of the Earth and resonant capture of solar 57-Fe axions
F. A. Danevich,A. V. Ivanov,V. V. Kobychev,V. I. Tretyak
Physics , 2008, DOI: 10.3103/S0884591309020056
Abstract: In a very conservative approach, supposing that total heat flow of the Earth is exclusively due to resonant capture inside the Earth of axions, emitted by 57-Fe nuclei on Sun, we obtain limit on mass of hadronic axion: m_a<1.8 keV. Taking into account release of heat from decays of 40-K, 232-Th, 238-U inside the Earth, this estimation could be improved to the value: m_a<1.6 keV. Both the values are less restrictive than limits set in devoted experiments to search for 57-Fe axions (m_a<216-745 eV), but are much better than limits obtained in experiments with 83-Kr (m_a<5.5 keV) and 7-Li (m_a<13.9-32 keV).
YAG:Nd crystals as possible detector to search for double beta and alpha decay of neodymium
F. A. Danevich,V. V. Kobychev,S. S. Nagorny,V. I. Tretyak
Physics , 2004, DOI: 10.1016/j.nima.2004.12.014
Abstract: Energy resolution, alpha/beta ratio, pulse-shape discrimination for gamma rays and alpha particles, radioactive contamination were studied with neodymium doped yttrium-aluminum garnet (YAG:Nd). Applicability of YAG:Nd scintillators to search for double beta decay and alpha activity of natural neodymium isotopes are discussed.
Quest for double beta decay of 160-Gd and Ce isotopes
F. A. Danevich,V. V. Kobychev,O. A. Ponkratenko,V. I. Tretyak,Yu. G. Zdesenko
Physics , 2000, DOI: 10.1016/S0375-9474(01)00983-6
Abstract: The double beta decay study of 160-Gd has been performed in the Solotvina Underground Laboratory with the help of Gd_2SiO_5(Ce) crystal scintillator (volume 95 cc). The background of the detector in the vicinity of the 2 beta energy of 160-Gd was reduced to 1.0 cpd/keV kg. The new improved half-life limits have been established for neutrinoless 2 beta decay of 160-Gd to the ground and first excited levels of 160-Dy: T1/2 > 2.3(1.3)E21 yr at 68%(90%) C.L. The T1/2 bounds have been also set for two neutrino mode as well as for 2 beta decay with Majorons emission. Also the limits were established for different 2 beta decay processes in 136-Ce, 138-Ce and 142-Ce.
ZnWO_4 crystals as detectors for double beta decay and dark matter experiments
F. A. Danevich,V. V. Kobychev,S. S. Nagorny,D. V. Poda,V. I. Tretyak,S. S. Yurchenko,Yu. G. Zdesenko
Physics , 2004, DOI: 10.1016/j.nima.2005.01.303
Abstract: Energy resolution, alpha/beta ratio, and the pulse shape discrimination ability of the ZnWO_4 crystal scintillators were studied. The radioactive contamination of a ZnWO_4 crystal was investigated in the Solotvina Underground Laboratory. Possibilities to apply ZnWO_4 crystals for the dark matter and double beta decay searches are discussed. New improved half-life limits on double beta decay in zinc isotopes were established, in particular, for EC\beta^+ decay of 64-Zn as: T_1/2^2nu > 8.9 10^18 yr and T_1/2^0nu > 3.6 10^18 yr, both at 68% CL.
Final results of an experiment to search for 2beta processes in zinc and tungsten with the help of radiopure ZnWO4 crystal scintillators
P. Belli,R. Bernabei,F. Cappella,R. Cerulli,F. A. Danevich,S. d'Angelo,A. Incicchitti,V. V. Kobychev,D. V. Poda,V. I. Tretyak
Physics , 2011, DOI: 10.1088/0954-3899/38/11/115107
Abstract: A search for the double beta decay of zinc and tungsten isotopes has been performed with the help of radiopure ZnWO4 crystal scintillators (0.1-0.7 kg) at the Gran Sasso National Laboratories of the INFN. The total exposure of the low background measurements is 0.529 kg yr. New improved half-life limits on the double beta decay modes of 64Zn, 70Zn, 180W, and 186W have been established at the level of 10^{18}-10^{21} yr. In particular, limits on double electron capture and electron capture with positron emission in 64Zn have been set: T_{1/2}(2\nu 2K) > 1.1 10^{19} yr, T_{1/2} (0\nu 2\epsilon) > 3.2 10^{20} yr, T_{1/2} (2\nu \epsilon \beta^+) > 9.4 10^{20} yr, and T_{1/2} (0\nu \epsilon \beta^+) > 8.5 10^{20} yr, all at 90% C.L. Resonant neutrinoless double electron capture in 180W has been restricted on the level of T_{1/2} (0\nu 2\epsilon) > 1.3 10^{18} yr. A new half-life limit on alpha transition of 183W to the metastable excited level 1/2^- 375 keV of 179Hf has been established: T_{1/2} > 6.7 10^{20} yr.
Potential of a next generation neutrinoless double beta decay experiment based on ZnMoO4 scintillating bolometers
J. W. Beeman,F. A. Danevich,V. Ya. Degoda,E. N. Galashov,A. Giuliani,V. V. Kobychev,M. Mancuso,S. Marnieros,C. Nones,E. Olivieri,G. Pessina,C. Rusconi,V. N. Shlegel,V. I. Tretyak,Ya. V. Vasiliev
Physics , 2011, DOI: 10.1016/j.physletb.2012.03.009
Abstract: The search for neutrinoless double beta decay probes lepton number conservation with high sensitivity and investigates the neutrino nature and mass scale. Experiments presently in preparation will cover the quasi-degeneracy region of the neutrino mass pattern. Probing the so-called inverted hierarchy region requires improved sensitivities and next-generation experiments, based either on large expansions of the present searches or on new ideas. We examine here the potential of a novel technology relying on ZnMoO4 scintillating bolometers, which can provide an experiment with background close to zero in the ton x year exposure scale. The promising performance of a pilot detector is presented, both in terms of energy resolution and background control. A preliminary study of the sensitivities of future experiments shows that the inverted hierarchy region is within the reach of the technique here proposed. A realistic phased approach program towards a next-generation search is presented and briefly discussed.
Search for long-lived superheavy eka-tungsten with radiopure ZnWO$_4$ crystal scintillator
P. Belli,R. Bernabei,F. Cappella,R. Cerulli,F. A. Danevich,V. Yu. Denisov,A. d'Angelo,A. Incicchitti,V. V. Kobychev,D. V. Poda,O. G. Polischuk,V. I. Tretyak
Physics , 2015, DOI: 10.1088/0031-8949/90/8/085301
Abstract: The data collected with a radioactively pure ZnWO$_4$ crystal scintillator (699 g) in low background measurements during 2130 h at the underground (3600 m w.e.) Laboratori Nazionali del Gran Sasso (INFN, Italy) were used to set a limit on possible concentration of superheavy eka-W (seaborgium Sg, Z = 106) in the crystal. Assuming that one of the daughters in a chain of decays of the initial Sg nucleus decays with emission of high energy $\alpha$ particle ($Q_\alpha > 8$ MeV) and analyzing the high energy part of the measured $\alpha$ spectrum, the limit N(Sg)/N(W) < 5.5 $\times$ 10$^{-14}$ atoms/atom at 90% C.L. was obtained (for Sg half-life of 10$^9$ yr). In addition, a limit on the concentration of eka-Bi was set by analysing the data collected with a large BGO scintillation bolometer in an experiment performed by another group [L. Cardani et al., JINST 7 (2012) P10022]: N(eka-Bi)/N(Bi) < 1.1 $\times$ 10$^{-13}$ atoms/atom with 90% C.L. Both the limits are comparable with those obtained in recent experiments which instead look for spontaneous fission of superheavy elements or use the accelerator mass spectrometry.
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