Composition and Electronic Structure of La₂O₃/CNFs@C Core-Shell Nanoparticles with Variable Oxygen Content

La2O3 nanoparticles stabilized on carbon nanoflake (CNF) matrix were synthesized and graphitized to produce core-shell structures La2O3/CNFs@C. Further oxidation of these structures by nitric acid vapors for 1, 3 or 6 h was performed, and surface-oxidized particles La2O3/CNFs@C_x (x = 1, 3, 6) were produced. Bulk and surface compositions of La2O3/CNFs@C and La2O3/CNFs@C_x were investigated by thermogravimetric analysis and X-ray photoelectron spectroscopy. With increasing the duration of oxidation, the oxygen and La2O3 content in the La2O3/CNFs@C_x samples increased. The electronic structures of samples were assessed by electron paramagnetic resonance. Two paramagnetic centers were associated with unpaired localized and mobile electrons and were registered in all samples. The correlation between bulk and surface compositions of the samples and their electronic structures was investigated for the first time. The impact of the ratio between sp2- and sp3-hybridized C atoms, the number and nature of oxygen-containing groups on the surface and the presence and proportion of coordinated La atoms on the EPR spectra was demonstrated

New Composite Contrast Agents Based on Ln and Graphene Matrix for Multi-Energy Computed Tomography

The subject of the current research study is aimed at the development of novel types of contrast agents (CAs) for multi-energy computed tomography (CT) based on Ln–graphene composites, which include Ln (Ln = La, Nd, and Gd) nanoparticles with a size of 2–3 nm, acting as key contrasting elements, and graphene nanoflakes (GNFs) acting as the matrix. The synthesis and surface modifications of the GNFs and the properties of the new CAs are presented herein. The samples have had their characteristics determined using X-ray photoelectron spectroscopy, X-Ray diffraction, transmission electron microscopy, thermogravimetric analysis, and Raman spectroscopy. Multi-energy CT images of the La-, Nd-, and Gd-based CAs demonstrating their visualization and discriminative properties, as well as the possibility of a quantitative analysis, are presented

Measurement of the radiation environment of the ATLAS cavern in 2017-2018 with ATLAS-GaAsPix detectors

A network of ten GaAs:Cr semiconductor Timepix detectors with GaAs:Cr sensors was installed in the ATLAS cavern at CERN’s LHC during the shutdown periods 2015–2016 and 2016–2017 in the framework of a cooperation between ATLAS and the Medipix2 Collaboration. The purpose was to augment the existing system of measuring and characterising the radiation environment in the ATLAS cavern that is based on ATLAS-TPX devices with pixelated silicon sensors. The detectors were in continuous operation during 13 TeV proton-proton collisions in 2017–2018. Data were recorded during proton-proton bunch crossings, and during times without bunch crossings (LHC physics runs) aswell as between the physics runs. The overall level of particle radiation as well as the ratio between neutral and charged particles were measured. The detectors recorded all interactions of charge particles, neutrons and photons in GaAs sensors, in which the signal was higher than 6.5 keV in individual pixels. This made it possible to register clusters (tracks) of individual radiation particles interacting in the detectors sensors. During LHC beambeam collisions, these were all particles represented in the radiation field. In the periods without beam-beam collisions, these were photons and electrons resulting from radioactivity induced during previous collisions in GaAs detectors and in surrounding construction materials, namely by neutrons

Registration of the transition radiation with GaAs detector: Data/MC comparison

New developments of pixel detectors based on GaAs sensors offer effective registration of the transition radiation (TR) X-rays and perform simultaneous measurements of their energies and emission angles. This unique feature opens new possibilities for particle identification on the basis of maximum available information about generated TR photons. Results of studies of TR energy-angular distributions using a 500 um thick GaAs sensor attached to a Timepix3 chip are presented. Measurements, analysis techniques and a comparison with Monte Carlo (MC) simulations are described and discussed

Determination of the number of ψ(3686)\psi(3686) events at BESIII

The numbers of ψ(3686) events accumulated by the BESIII detector for the data taken during 2009 and 2012 are determined to be and , respectively, by counting inclusive hadronic events, where the uncertainties are systematic and the statistical uncertainties are negligible. The number of events for the sample taken in 2009 is consistent with that of the previous measurement. The total number of ψ(3686) events for the two data taking periods is