Search

In this study, we investigate etched channels of a special shape that arise during the search for superheavy nuclei in olivines from meteorites. The possibility of the appearance of tracks of this shape due to electrons penetrating olivine at a distance of several microns from the track is considered. The calculation results related to the spatio-temporal development of an electron shower during the passage of a heavy ion through olivine are presented. It has been shown that it is not possible to explain the observed effect only by the presence of δ electrons. In addition, the correspondence of a number of assumptions of some models of ion passage through matter to the obtained characteristics of δ electrons is discussed.

Cosmic ray muonography is a novel technique for imaging of the internal structures of large natural and industrial objects. It exploits the capability of high energy muons from cosmic rays to penetrate large thicknesses of large subjects to be studied, in order to obtain a density map. It uses muon flux attenuation and absorption in materials of investigated objects. Nuclear emulsions are tracking detectors well suited to be employed in muonography for investigations of inner structure of large objects up to kilometers size, since emulsions have firstly an excellent angular resolution, they are compact and robust, do not require power supply. The muonography methods are applied to study one of UNESCO world heritage objects, the unusual building in the Naryn-Kala citadel hidden underground. The use of nuclear emulsions as probing radiation detectors provides for a uniquely high resolution capacity of recording instrumentation combined with the potential of modern image analysis methods giving 3D reconstruction of the internal structures of the investigated object.

About 0.85 × 105 events involving stopped μ + and muonium decay were observed in a nuclear photoemulsion with the aim of searches for a light dark photon (DPh) in the decay process DPh → e + e −. With a probability of about 10−5, no event of the decay μ+ → е + ν μ ν е accompanied by an electron–positron pair was observed. In the interval of 1.1 MeV ≤ m DPh ≤ 60 MeV, the mixing parameter e 2 was estimated at about 10−5 to 10−4.

In Russia, the Lebedev Physical Institute of the Russian Academy of Sciences and the Skobeltsyn Institute of Nuclear Physics of Moscow State University are starting a series of pilot muon radiography exper-iments with nuclear emulsion detectors to study the interior structure of large-scale natural and industrial objects. As a result, the optimal conditions for experimental organization have been determined, algorithms of data processing have been worked out, and peculiarities of the method have been ultimately investigated. Here we present the experimental data, including field observations (in the mine of Geophysical department of Russian Academy of Sciences) confirming the availability of the method with track detectors on the base of nuclear emulsions with uniquely high spatial resolution, providing their high-tech automated processing.

The charge distribution of approximately 6000 nuclei with charge numbers above 55 in galactic cosmic rays has been obtained in the OLIMPIYA project. Three superheavy nuclei with the charge numbers in the range 105 92 are due to the fragmentation of heavier nuclei from the stability island, rather than to methodical inaccuracies or fault of instruments. Several such events have been revealed. Thus, the track method makes it possible to obtain the results very important for understanding of the physical picture of the world. The results obtained within the OLIMPIYA project show that the study of tracks of galactic cosmic rays in olivine crystals from meteorites opens new capabilities for the investigation of fluxes and spectra in cosmic rays in the region of heavy and superheavy nuclei.

This work reviews the status of the international OPERA experiment aimed at searching for the νμ → ντ oscillation. Development of the emulsion techniques in the preceding DONUT and CHORUS experiments is described. A brief overview of the NOMAD experiment is given, in which properties of ντ interactions were thoroughly investigated. Characteristics of the CERN-Gran Sasso (CNGS) neutrino beam are given, the structure of the OPERA hybrid detector and the functions of its subsystems are considered, and the automatic emulsion scanning technique is briefly reviewed. Uncertainties in reconstruction of event parameters using the electronic and emulsion detectors are discussed and the procedure adopted in the experiment for identification of ντ interactions is described. The main sources of background in the search for νμ → ντ oscillation are considered. Topologies of the first two ντ candidates observed in the OPERA emulsion detector are presented. Possibilities of increasing the ντ interaction selection efficiency using multidimensional criteria are briefly discussed.

Nuclear emulsion was exposed to xenon nuclei accelerated at the JINR Nuclotron. Visual and automated scanning of the extracted beam profile was performed using the exposed emulsion film.

An experimental method is proposed for investigating the structure of the two-neutron halo in quasifree proton scattering on clusters of halo nuclei. This scattering process is studied in inverse kinematics by using a 6He beam incident to a stack of track emulsions. Preliminary data on the reaction 6He + p → 4He + p + X are compared with the results of simple kinematical calculations for quasifree proton scattering on the clusters forming the halo of the 6He nucleus.

To identify the charge of detected cosmic ray nuclei, it is necessary that the dynamic and geometric parameters of tracks (the etching rate of a nuclear track, as well as the length and the diameter of the track channel) be determined with a high accuracy. Results of the experimental investigations of tracks produced in olivine crystals from the Marjalahti pallasite by accelerated Xe and U nuclei are presented. These investigations were performed as part of the Olimpiya project. It is shown that the etching rate and the fully etched track length are independent of the track orientation relative to the crystallographic symmetry axes of each olivine crystal under investigation.

A technique for measuring the charges of relativistic nuclei in thick emulsion layers irradiated in a longitudinal direction is described. This technique has been implemented on the PAVICOM completely auto- mated facility at the Lebedev Physical Institute. The calibration curves for relativistic nuclei with Z > 3 are pre- sented. The advantages of this technique are demonstrated using charge measurements of 28 Si nuclear frag- ments as an example. PACS numbers: 29.40.Rg, 29.85.+c DOI: 10.1134/S0020441207040070

In this paper, we consider the nuclear-physical and astrophysical aspects of investigations associated with the search for heavy and superheavy nuclei in the composition of cosmic rays. We also discuss the potentiality of searching for tracks of these nuclei in the olivine crystals found in meteorites with the use of the completely automated PAVICOM setup, which was designed for the scanning and processing of tracks of particles.

The electron-photon shower development in a lead plate-emulsion sandwich chamber with a total effective lead thickness of 3.5 radiation units was studied for an electron energy of 26 GeV. The experimental electron multiplication coefficient (Pexp=19.4±1.4) agrees with a theoretical value (Pcalcd=20.4) calculated with corrections for the particle scattering and absorption.