arXiv subjects

S. Tkachenko

Publications and source records attributed to S. Tkachenko.

7 recordsLinked to original sources

arXiv2024

Exploring Scintillators and Cherenkov Radiators for MIP Timing Detectors

This article presents the timing performance of materials with fast light emission, tested as Minimum Ionizing Particle detectors using 150 GeV hadron beams in Monte Carlo simulations and at the CERN SPS North Area. Pixels of cross-section 2 x 2 mm2 or 3 x 3 mm2 and length of 3 or 10 mm were coupled to Hamamatsu SiPM and read out by fast high-frequency electronics. Materials whose timing performance relies on Cherenkov emission, namely BGSO, PWO, and PbF2, achieved time resolutions in the range 24-36ps. Scintillators as L(Y)SO:Ce, GAGG, and BaF2 reached below 15 ps, the best topping at 12.1 +/- 0.4 ps. These fast materials are compared to LYSO and their additional benefit is discussed. Given the promising results of BaF2, the study is completed with measurements of the scintillation properties of a set doped with yttrium to quench the slow light emission.

physics.ins-det↗

arXiv2018

Oxygen-vacancy centers in Y3Al5O12 garnet crystals: electron paramagnetic resonance and dielectric spectroscopy study

F+ center, an electron trapped at oxygen vacancy (VO), was investigated in the oxygen deficient Y3Al5O12 (YAG) crystals by EPR. The measurements were performed at temperatures 5-450 K and frequencies 9.4-350 GHz with using both the continue wave and pulse EPR technique. The pulse electron-nuclear double resonance was applied to resolve the hyperfine interaction of the trapped electron with surrounding nuclei. The measurements show that at low temperatures, T < 50 K, EPR spectrum of the F+ center is anisotropic with g factors in the range 1.999-1.988 and originates from three magnetically inequivalent positions of the center in garnet lattice according to different directions of the Al(IV)-VO-Al(VI) chains, where Al(IV) and Al(VI) are the tetrahedral and octahedral Al sites, respectively. As the temperature increases, the EPR spectrum becomes isotropic suggesting a motional averaging of the anisotropy due to motion of electron between neighboring oxygen vacancies. With further increase of the temperature to T > 200 K, we observed delocalization of the electron into the conduction band with the activation energy about 0.4-0.5 eV that resulted in substantial narrowing of the EPR spectral line with simultaneous change of its shape from the Gaussian to Lorentzian due to diminish up to zero of the Fermi contact hyperfine field at 27Al and 89Y nuclei. Such temperature behavior of the F+-center electron in YAG is completely similar to behavior of a donor electron in a semiconductor. Our findings is further supported by measurements of the conductivity and dielectric properties. In particular, these data show that the conduction electrons are not homogeneously distributed in the crystal: there are high-conductive regions separated by poorly-conductive dielectric layers. This leads to the so-called Maxwell-Wagner dielectric relaxation with huge apparent dielectric constant at low frequencies.

cond-mat.mtrl-sci↗

arXiv2015

Measurement of the EMC Effect in the Deuteron

We have determined the structure function ratio $R^d_{\rm EMC}=F_2^d/(F_2^n+F_2^p)$ from recently published $F_2^n/F_2^d$ data taken by the BONuS experiment using CLAS at Jefferson Lab. This ratio deviates from unity, with a slope $dR_{\rm EMC}^{d}/dx= -0.10\pm 0.05$ in the range of Bjorken $x$ from 0.35 to 0.7, for invariant mass $W>1.4$ GeV and $Q^2>1$ GeV$^2$. The observed EMC effect for these kinematics is consistent with conventional nuclear physics models that include off-shell corrections, as well as with empirical analyses that find the EMC effect proportional to the probability of short-range nucleon-nucleon correlations.

hep-ph↗

arXiv2015

Direct observation of quark-hadron duality in the free neutron F_2 structure function

Using data from the recent BONuS experiment at Jefferson Lab, which utilized a novel spectator tagging technique to extract the inclusive electron-free neutron scattering cross section, we obtain the first direct observation of quark-hadron duality in the neutron F_2 structure function. The data are used to reconstruct the lowest few (N=2, 4 and 6) moments of F_2 in the three prominent nucleon resonance regions, as well as the moments integrated over the entire resonance region. Comparison with moments computed from global parametrizations of parton distribution functions suggest that quark--hadron duality holds locally for the neutron in the second and third resonance regions down to Q^2 ~ 1 GeV^2, with violations possibly up to 20% observed in the first resonance region.

hep-ex↗

arXiv2014

Measurement of the structure function of the nearly free neutron using spectator tagging in inelastic $^2$H(e, e'p)X scattering with CLAS

Much less is known about neutron structure than that of the proton due to the absence of free neutron targets. Neutron information is usually extracted from data on nuclear targets such as deuterium, requiring corrections for nuclear binding and nucleon off-shell effects. These corrections are model dependent and have significant uncertainties, especially for large values of the Bjorken scaling variable x. The Barely Off-shell Nucleon Structure (BONuS) experiment at Jefferson Lab measured the inelastic electron deuteron scattering cross section, tagging spectator protons in coincidence with the scattered electrons. This method reduces nuclear binding uncertainties significantly and has allowed for the first time a (nearly) model independent extraction of the neutron structure function. A novel compact radial time projection chamber was built to detect protons with momentum between 70 and 150 MeV/c. For the extraction of the free neutron structure function $F_{2n}$, spectator protons at backward angle and with momenta below 100 MeV/c were selected, ensuring that the scattering took place on a nearly free neutron. The scattered electrons were detected with Jefferson Lab's CLAS spectrometer. The extracted neutron structure function $F_{2n}$ and its ratio to the deuteron structure function $F_{2d}$ are presented in both the resonance and deep inelastic regions. The dependence of the cross section on the spectator proton momentum and angle is investigated, and tests of the spectator mechanism for different kinematics are performed. Our data set can be used to study neutron resonance excitations, test quark hadron duality in the neutron, develop more precise parametrizations of structure functions, as well as investigate binding effects (including possible mechanisms for the nuclear EMC effect) and provide a first glimpse of the asymptotic behavior of d/u as x goes to 1.

nucl-ex↗

arXiv2012

Measurement of the neutron F2 structure function via spectator tagging with CLAS

We report on the first measurement of the F2 structure function of the neutron from semi-inclusive scattering of electrons from deuterium, with low-momentum protons detected in the backward hemisphere. Restricting the momentum of the spectator protons to < 100 MeV and their angles to < 100 degrees relative to the momentum transfer allows an interpretation of the process in terms of scattering from nearly on-shell neutrons. The F2n data collected cover the nucleon resonance and deep-inelastic regions over a wide range of Bjorken x for 0.65 < Q2 < 4.52 GeV2, with uncertainties from nuclear corrections estimated to be less than a few percent. These measurements provide the first determination of the neutron to proton structure function ratio F2n/F2p at 0.2 < x < 0.8 with little uncertainty due to nuclear effects.

nucl-ex↗

arXiv2011

Radioactive contamination of SrI2(Eu) crystal scintillator

A strontium iodide crystal doped by europium (SrI2(Eu)) was produced by using the Stockbarger growth technique. The crystal was subjected to a characterization that includes relative photoelectron output and energy resolution for gamma quanta. The intrinsic radioactivity of the SrI2(Eu) crystal scintillator was tested both by using it as scintillator at sea level and by ultra-low background HPGe gamma spectrometry deep underground. The response of the SrI2(Eu) detector to alpha particles (alpha/beta ratio and pulse shape) was estimated by analysing the 226Ra internal trace contamination of the crystal. We have measured: alpha/beta=0.55 at E_alpha=7.7 MeV, and no difference in the time decay of the scintillation pulses induced by alpha particles and gamma quanta. The application of the obtained results in the search for the double electron capture and electron capture with positron emission in 84Sr has been investigated at a level of sensitivity: T_1/2 \sim 10^{15}-10^{16} yr. The results of these studies demonstrate the potentiality of this material for a variety of scintillation applications, including low-level counting experiments.

physics.ins-det↗