Institute for Nuclear Research of Ukraine

Kiev, Ukraine

Institute for Nuclear Research of Ukraine

Kiev, Ukraine
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Tretyak V.I.,Institute for Nuclear Research of Ukraine | Tretyak V.I.,Seoul National University
Astroparticle Physics | Year: 2010

Semi-empirical method of calculation of quenching factors for scintillators is described. It is based on classical Birks formula with the total stopping powers for electrons and ions which are calculated with the ESTAR and SRIM codes, respectively. Method has only one fitting parameter (the Birks factor kB) which can have different values for the same material in different conditions of measurements and data treatment. A hypothesis is used that, once the kB value is obtained by fitting data for particles of one kind and in some energy region (e.g. for a few MeV α particles from internal contamination of a detector), it can be applied to calculate quenching factors for particles of another kind and for another energies (e.g. for low energy nuclear recoils) if all data are measured in the same experimental conditions and are treated in the same way. Applicability of the method is demonstrated on many examples including materials with different mechanisms of scintillation: organic scintillators (solid C8 H8, and liquid C16 H18, C9 H12); crystal scintillators (pure CdWO4, PbWO4, ZnWO4, CaWO4, CeF3, and doped CaF2(Eu), CsI(Tl), CsI(Na), NaI(Tl)); liquid noble gases (LXe). Estimations of quenching factors for nuclear recoils are also given for some scintillators where experimental data are absent (CdWO4, PbWO4, CeF3, Bi4 Ge3 O12, LiF, ZnSe). © 2009 Elsevier B.V. All rights reserved.

Ivanyuk F.A.,Institute for Nuclear Research of Ukraine
Physics Procedia | Year: 2013

The scission of a nucleus into two fragments is at present the least understood part of the fission process, though the most important for the formation of the observables. To investigate the potential energy landscape at the largest possible deformations, i.e. at the scission point (line, hypersurface), the Strutinsky's optimal shape approach is applied. For the accurate description of the mass-asymmetric nuclear shape at the scission point, it turned out necessary to construct an interpolation between the two sets of constraints for the elongation and mass asymmetry which are applied successfully at small deformations (quadrupole and octupole moments) and for separated fragments (the distance between the centers of mass and the difference of fragments masses). In addition, a constraint on the neck radius was added, what makes it possible to introduce the so called super-short and super-long shapes at the scission point and to consider the contributions to the observable data from different fission modes. The calculated results for the mass distribution of the fission fragment and the Coulomb repulsion energy "immediately after scission" are in a reasonable agreement with experimental data. © 2013 The Authors.

Sugakov V.I.,Institute for Nuclear Research of Ukraine | Vertsimakha G.V.,Institute for Nuclear Research of Ukraine
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Effects of the resonant interaction between an exciton in a semiconductor quantum well and localized plasmon excitations in a spherical metal nanoparticle are studied. The calculations show that (1) if the exciton energy level is lower than the energy of the plasmon, the exciton-plasmon interaction may result in the localization of the exciton as a whole in the vicinity of the nanoparticle; (2) a giant (by several orders of magnitude) increase in the oscillator strength of the localized exciton transition takes place near the resonance between the exciton and the plasmon levels. The energy of the lowest excited level of the system was calculated by the variational method, the dependence of the localized exciton energy on the distance between the particle, and the quantum well as well as on the particle radius was obtained. © 2010 The American Physical Society.

Danevich F.A.,Institute for Nuclear Research of Ukraine
IEEE Transactions on Nuclear Science | Year: 2012

Experiments to search for neutrinoless double beta decay are considered as an unique tool to study properties of neutrino and weak interactions. Scintillation detectors possess important properties required for high-sensitivity double beta decay experiments: presence of elements of interest, low level of intrinsic radioactivity, reasonable spectrometric characteristics, fast response, pulse-shape discrimination ability. Moreover, some crystal scintillators can be applied as cryogenic scintillating bolometers with high energy resolution and excellent particle discrimination. High concentration of isotope of interest and as low as possible radioactive contamination are important requirements to a scintillation material to be used in double beta decay experiments. Therefore development of radiopure crystal scintillators from isotopically enriched materials is required. Other important issues are maximal output of detectors and minimal loss of enriched materials. High quality, radiopure cadmium tungstate crystal scintillators were developed from enriched 106 and 116, while calcium molybdate scintillators were grown form calcium depleted in 48 Ca and molybdenum enriched in 100 Mo. Prospects of several scintillation materials, promising for double beta experiments, are discussed. © 2012 IEEE.

Marchenko V.S.,Institute for Nuclear Research of Ukraine
Physics of Plasmas | Year: 2014

Tokamak discharges with extended weak-shear central core are known to suffer from infernal modes when the core safety factor approaches the mode ratio. These modes can cause an outward convection of the well-passing energetic ions deposited in the core by fusion reactions and/or neutral beam injection. Convection mechanism consists in collisional slowing down of energetic ions trapped in the Doppler-precession resonance with a finite-amplitude infernal mode. Convection velocity can reach a few m/s in modern spherical tori. Possible relation of this transport with the enhanced fast ion losses in the presence of " long lived modes" in the MAST tokamak [I. T. Chapman et al., Nucl. Fusion 50, 045007 (2010)] is discussed. © 2014 AIP Publishing LLC.

Denisov V.Yu.,Institute for Nuclear Research of Ukraine
Physical Review C - Nuclear Physics | Year: 2013

The cluster decays 228Th→208Pb+20O, 232U→208Pb+24Ne, 236Pu→208Pb+28Mg, and 242Cm→208Pb+34Si are considered in the framework of the multidimensional cluster-preformation model. The macroscopic potential-energy surface related to the interaction between the cluster and the residue nucleus is evaluated in the framework of the nonlocal â4 extended Thomas-Fermi approach with Skyrme and Coulomb forces. The shell correction to the macroscopic potential energy is also taken into account. The dynamical surface deformations of both the cluster and the residue nucleus are taken into consideration at the barrier penetration path. The heights of saddle points related to deformed nuclear shapes are lower than the barrier height between the spherical cluster and residue nuclei; therefore the dynamical deformations of nuclei increase the barrier penetrability and reduce the half-life of cluster decay. The shell-correction contribution into the potential energy between cluster and residue nucleus is important for both the potential landscape and the half-life evaluation. The experimental values of cluster-decay half-lives are well reproduced in the model. © 2013 American Physical Society.

Denisov V.Y.,Institute for Nuclear Research of Ukraine | Khudenko A.A.,Institute for Nuclear Research of Ukraine
Physical Review C - Nuclear Physics | Year: 2010

The α-decay half-lives of even-even superheavy elements within the range of proton number 104≤Z≤126, which can be formed by possible cold and hot fusion reactions, are calculated in the framework of various approaches for α-decay half-life evaluation and by using the Q values of α transitions obtained within different approximations for atomic masses. The dependencies of α-decay half-lives of superheavy elements on model approaches for both the Q values and half-life calculations are discussed in detail. © 2010 The American Physical Society.

Ivanyuk F.A.,Institute for Nuclear Research of Ukraine
Physica Scripta | Year: 2014

In the present work the formal definition of the scission point - the maximal elongation at which the nucleus splits into two fragments - is given. The shape and the deformation energy at the scission point are calculated using the macroscopic-microscopic model. Three minima in the scission point deformation energy are found corresponding to the 'standard', 'supershort' and 'superlong' fission modes. The contribution of each fission mode to the mass distribution of the fission fragments and total kinetic energy is discussed and compared with the experimental results. In the example of the fission of U-235 by thermal neutrons it is shown that the present approach reproduces correctly the position of the peaks of the mass distribution of the fission fragments, the value and the fine details of the total kinetic energy distribution and the magnitude of the total excitation energy of the fission fragments. © 2014 The Royal Swedish Academy of Sciences.

Dzyublik A.Y.,Institute for Nuclear Research of Ukraine
JETP Letters | Year: 2011

The nuclear excitation at electron transition (NEET), induced by X rays, is described on the basis of strict collision theory. All stages of the process are considered, including formation of the hole in the electron K shell, its decay accompanied by excitation of the nucleus, filling of the M-vacancy and subsequent deexcitation of the nucleus. The cross sections for the NEET and photoabsorption of X rays near K-edge are calculated. The results agree with the data of Kishimoto et al. © 2011 Pleiades Publishing, Ltd.

Denisov V.Y.,Institute for Nuclear Research of Ukraine
Physical Review C - Nuclear Physics | Year: 2014

It is suggested that the full nucleus-nucleus potential consists of the macroscopic and shell-correction parts. The deep sub-barrier fusion hindrance takes place in a nucleus-nucleus system with a strong negative shell-correction contribution to the full heavy-ion potential, while a strong positive shell-correction contribution to the full potential leads to weak enhancement of the deep sub-barrier fusion cross section. © 2014 American Physical Society.

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