Vol 82, No 9 (2019)

In the context of the search for the triples of relativistic α particles in the Hoyle state, the analysis of available data on the dissociation of the ¹²C, ¹⁶O, and ²²Ne nuclei in a nuclear track emulsion was carried out. The Hoyle state is identified by the invariant mass calculated from the pair opening angles in α triples in the approximation of the conservation of the momentum per nucleon of the parent nucleus. The contribution of the Hoyle state to the ¹²C → 3α dissociation is 10%. In the case of the ¹⁶O → 4α coherent dissociation, it reaches 22% when the portion of the ¹⁶O → 2⁸Be channel is 5%.

The paper reports results of studying the geometry of craters formed by the action of laser pulses on solid-state targets of aluminum and lithium films at a power density on the target of (1–5) × 10¹⁰ W/cm² and variation of the number of pulses in the range of 1–150, as well as the results of ex situ layer-by-layer analysis of lithium films on quartz coatings carried out using the method laser induced breakdown spectroscopy to determine the thickness of the films.

The new results of cathode surface degradation in muon proportional chambers of CMS after a long-term irradiation with a ⁹⁰Sr β-source are presented. The data of the complex analysis of the copper foil samples from the cathode are shown. The AFM method revealed the general radiation damage of the copper surface and the dynamics of its change. It is clearly demonstrated that the revealed development of the radiation erosion on the cathode is a result of electron irradiation. Moreover, the nature of erosion and level of the destruction of copper are associated with irradiation intensity. The study of the elemental and phase composition together with the data of structural analysis allowed us to single out the stages of the radiation aging of the copper surface on the cathodes and consider the processes which are at the basis of them.

The uniformity of composition of rapidly quenched PREP particles of the powder of high temperature Ni-based superalloys and stainless steels is characterized by an important feature—the occurrence of anomalous particles (granules) with a significantly different content, mainly of microalloying interstitial elements, carbon and boron, as well as active carbide- and boride-forming alloying elements. A detailed multi-scale experimental study of the heating zone of the crater of the Ni-based superalloy electrode after its use to obtain rapidly quenched PREP powder was carried out in order to find the nature and mechanisms of the formation of anomalous granules. Direct nuclear physics methods of activation autoradiography on carbon, track autoradiography on boron, metallography, SEM, EDX, OIM were used. In the electrode crater, the heat-affected zone (HAZ) and the partially melted zone (PMZ) were detected. Intense migration of boron to the electrode surface due to the formation of thermal macrocracks was also revealed. The behavior of carbon is determined by the formation of a thin layer of melt on the surface of the crater. The features of the evolution of the terminal solidification region TSR and incipiently melted regions IMR, the main type of heterogeneity of the composition of the dendritic structure of Ni-based superalloys and stainless steels, are revealed. The interrelation of the evolution of these areas is established, which is a consequence of the thermodynamic principle of the reversibility of the processes of solidification and melting, respectively, in the smelting of an ingot electrode and in the process of subsequent atomization. The analysis of the influence of the behavior of boron, carbon, and the characteristics of the crater structure on the nature and mechanism of the formation of anomalous granules using the PREP method for producing rapidly quenched powder of the Ni-based superalloy is performed.

A method is presented for restoring the performance of gas discharge detectors wherein a spontaneous self-sustaining current, i.e., Malter effect, occurs. A successful practical implementation of the method is demonstrated by the example of recovery of operability for multiwire proportional chambers used in the muon detector of the LHCb experiment carried out at the Large Hadron Collider. Four proportional chambers wherein Malter currents regularly occur during the experiment were subjected to high-voltage discharge training in the working gas mixture of 40% Ar + 55% CO₂ + 5% CF₄ with 2% of oxygen added. It is shown that, with addition of oxygen, the recovery of the proportional chambers occurs tens of times faster in compare to the training in the working gas mixture. The reconstructed chambers were installed in the LHCb muon detector and have been working in a collider beam experiment for more than two years already.

Atom probe tomography (ATP) is a technique that has actively been developed in recent years. This method allows one to investigate three-dimensional distributions of chemical elements in various materials with atomic spatial resolution. The raw APT data reconstruction algorithm uses the geometry of evaporated ion trajectories. However, the basic algorithm uses the approximation of rectilinear trajectories of ions moving from the specimen to the detector. In this study, we present the main approaches to adapting and optimizing the basic APT data reconstruction algorithm concerning the mass reconstruction procedure. Methods for taking into account the nonlinear distortions of ion trajectories due to the wide-angle detection system and other features of ion detection in atom probe tomography are demonstrated. Using a titanium alloy (Ti—5Al—2.7Mo—2Zr), we demonstrate that the consideration of the above effects in the reconstruction of ATP data makes it possible to increase the mass resolution, m/Δm_50%, of the main peaks of the mass spectrum to 600 and above. In general, the set of performed procedures allows one to achieve a high accuracy of the positioning of the peaks up to 0.01 amu and ensures a significant (more than tenfold) increase in the mass resolution for mass spectrum peaks that are distant from the main peaks.

The design and the procedures for assembling and testing drift tubes 15 mm in diameter made of 125-µm-thick Mylar film with a double-sided aluminum coating are presented. The technology of assembling three-layer chambers made of such tubes with a length of up to 2.5 m intended for use in experiments at the accelerator facility at the Institute for High Energy Physics of the National Research Center Kurchatov Institute—IHEP is described. Some results obtained during detection of cosmic muon tracks in the chambers are presented.

Promising approaches and methods for studying nuclear matter at high baryonic densities and low temperatures are discussed.