The review presents the stages of modernization of the tracker system of the ATLAS detector at the Large Hadron Colider (LHC). The period from the moment of the detector creation to its further operation in the high luminosity mode of the HL-LHC is considered. Changes of the detector design at different stages, resolution when measuring tracks of charged particles, the quality of the recovery of vertices under conditions of high luminosity of the collider, leading to simultaneous recording of 200 events on average with the birth of two or more charged particles during collisions of proton bunches are shown. The physical goals are indicated, for the solution of which the realizable and planned changes of the ATLAS track system are critical.
Show AbstractOne of the main disadvantages of both classical and split microtron is a small region of stable phase oscillations, which directly affects the value of the output current of the accelerator, greatly reducing it. To increase it, an additional harmonic of the reproducing field is introduced in this paper. Theoretical calculations and computer modeling were performed, which showed an increase in the region when the second harmonic was added.
Show AbstractUsing objective physical reliability criteria, experimental data on the cross sections for partial photoneutron reactions on the 160Gd, obtained on the beams of quasimonoenergetic annihilation photons and methods for separation of neutron multiplicity were analyzed. It was established that the experimental cross sections of partial reactions (γ, 1n), (γ, 2n) and (γ, 3n) don’t satisfy the introduced criteria. The new data for partial and total photoneutron reactions for 160Gd cross sections were obtained using the experimental–theoretical method of evaluating the cross sections of the partial reactions, satisfying the reliability criteria. The noticeable deviations of the experimental cross sections from the evaluated once resulted from the unreliable sorting of neutrons between the channels with multiplicities were found.
Show AbstractWe consider spin correlations in top-quark t-channel production and subsequent decay process, including anomalous Wtb interactions. We use formalism of spinors in Weyl's representation to compute squared amplitude of the process. It is found that unique kinematic functions stay near every combinations of anomalous couplings, so this fact could be used to obtain further limits on anomalous couplings.
Show AbstractEvolution of nuclear structure concepts is traced from the simplest drop and single-particle shell models in view of the Thomas Jefferson Lab (USA) experiment, in which short-range correlations of nucleons in nuclei have been studied. It is argued that treatment of the short-range correlations requires theoretical consideration of subnucleonic (quark and gluonic) degrees of freedom in nuclei.
Show AbstractExperimental studies of the features of nonlinear propagation of harmonic acoustic waves in wedges made of an anisotropic lithium niobate crystal are carried out. The effect of fast dynamics, nonlinear absorption and generation of the second and third harmonics of the wedge elastic waves are observed.
Show AbstractThree models of multi-element ultrasound phased arrays for shock-wave surgical destruction of deep brain structures through an intact skull are proposed. The arrays contain 256, 512, and 1024 elements and have the maximum dense filling of their surface with the elements. Unlike the existing systems of ultrasound neurosurgery, these arrays can realize not a thermal but a mechanical mechanism of tissue ablation (boiling histotripsy). Such approach permits to avoid undesirable overheating and damage to the skull bones. The proposed arrays are much more compact as compared to the existing systems. The arrays have the shape of a spherical segment with an aperture of 200 mm, whereas existing arrays have the shape of a hemispherical bowl with a diameter of 300 mm. Comparative analysis of focus steering capabilities is performed and the possibility of creating volumetric lesions larger than 20 mm in each dimension is shown for all proposed arrays. Nonlinear simulation demonstrated the possibility of reaching focal waveforms with developed shock fronts higher than 70 MPa, required for boiling histotripsy method. Taking into account energy losses when focusing through the skull bones and brain tissues, the intensity at the elements of the arrays does not exceed maximum permissible value of 40 W/cm2.
Show AbstractThe use of fluorescent detectors is considered extremely promising for the registration of super-intensive X-ray beams. This is due to a number of advantages of such detectors in comparison with traditional detectors (such as CCD, diodes, X-ray films, etc.). In particular, this type of detectors has submicron spatial resolution, simultaneously with a large field of view (up to several cm2). It is also known that the dynamic range of a fluorescent detector ( lithium fluoride crystal – LiF) for soft X-ray radiation significantly exceeds the dynamic range of conventional detectors 1E4. In the framework of this work, the possibility of in-situ profile measurement of a focused synchrotron radiation with ultra-wide dynamic range 1E6 using a fluorescent detector (lithium fluoride crystal-LiF) and a confocal laser scanning microscope are presented.
Show AbstractThe luminescent-kinetic properties in the region of 1.5 µm of gradient-activated lith-ium niobate crystals inhomogeneously sensitized by optical Er3+ ions and impurity centers Ce3+, Zn2+ are studied, as well as the synthesized organic coordination compounds with op-tical centers of Yb3+ and Er3+ions are considered. As a result of the studies, it was found that in the samples sensitized with Ce3+ ions, a decrease in the luminescent lifetime of the excited state of 4I13/2 Er3+optical centers was observed. In organic coordination compounds, the opti-cal centers of erbium ions also show a decrease in the luminescent lifetime of the excited state. It was found that the decrease in the luminescent lifetime of the Er optical center in the region of 1.5 µm for LiNbO3:Er, Ce crystals compared to similar values in LiNbO3:Er is determined by the presence of Ce3+ ions in the matrix and the transfer of the electron excitation energy between the impurity centers. The presence of the concentration profile of Zn2+ ions in the crystal matrix of lithium niobate can potentially create conditions for the formation of non-equivalent optical centers for Er ions, similar to the effect on the optical centers of Mg2+nephotorefractive impurity ions. In organic coordination compounds, the decrease in the lifetime of the excited state can be explained by the exchange energy processes between the optical center and the coordination environment of the organic compound. In the investigated organic compounds, the decrease in the luminescent lifetime of Er3 + ions is due to the presence of coordination compounds and the exchange energy processes between the ions.
Show AbstractTaking a “rotating tube” as a starting point to demonstrate a rigid body motion peculiarities, several advanced options of such a things are offered to visualize the corresponding concepts in kinematics, with the instantaneous axis of rotation having a special priority. The significant difference in behavior of the devices under consideration from other nonlinear systems concerns the time needed for the achievement of stationary phases. The corresponding time intervals are found to be finite, as opposed to exponential ones widely spread in nonlinear processes – due to dry friction.
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