N. I. Starkov

Problems and horizons of the search for tracks of heavy and superheavy nuclei in olivine crystals from meteorites (OLIMPIYA project)

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.

Heavy-particle energy loss simulation using the Geant4 toolkit

Currently, the Geant4 is a standard tool for simulating experiments in high-energy physics. In this paper, we describe an improvement of the ionization model for hadrons, ions, and classical magnetic monopole, implemented in Geant4. Simulation results are discussed; their accuracy is analyzed depending on chosen parameters, and compared with experimental data.

Prospects of the Study of Geological Structures by Muon Radiography Based on Emulsion Track Detectors

For the first time in Russia, researchers of the Lebedev Physical Institute and Skobeltsyn Institute of Nuclear Physics perform test experiments for studying the internal structure of large natural and industrial objects by the muon radiography method using the emulsion technique. The used technique is based on the high penetrability of cosmic muons and implies the detection of the attenuation of their flux passed through the object under study using nuclear photoemulsions with a uniquely high spatial resolution. The results of the first test experiment are presented, which confirm the promising application of the method when using emulsion track detectors and their subsequent hi-tech automated processing.

Search for superheavy elements in galactic cosmic rays

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 < Z < 130 have been detected. The regression analysis has provided a more accurate estimate of the charge number of one of these nuclei (119−6+10 with a probability of 95%). Such nuclei should form stability islands. Their detection in nature confirms theoretical predictions and justifies efforts for their synthesis under terrestrial conditions. The model calculations performed in this work possibly can explain the results of some experiments on the investigation of the charge composition of cosmic rays in which particles with charge numbers in the range 94 < Z < 100 were detected (they cannot enter into the composition of primary cosmic radiation because their lifetime is very short). The calculations indicate that events with Z > 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.

Quasifree proton scattering on halo nuclei as a tool for studying the neutron-halo structure

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.

CHARGE SPECTRUM OF HEAVY AND SUPERHEAVY COMPONENTS OF GALACTIC COSMIC RAYS: RESULTS OF THE OLIMPIYA EXPERIMENT

The aim of the OLIMPIYA experiment is to search for and identify traces of heavy and superheavy nuclei of galactic cosmic rays (GCR) in olivine crystals from stony–iron meteorites serving as nuclear track detectors. The method is based on layer-by-layer grinding and etching of particle tracks in these crystals. Unlike the techniques of other authors, this annealing-free method uses two parameters: the etching rate along the track (V etch) and the total track length (L), to identify charge Z of a projectile. A series of irradiations with different swift heavy ions at the accelerator facilities of GSI (Darmstadt) and IMP (Lanzhou) were performed in order to determine and calibrate the dependence of projectile charge on V etch and L. To date, one of the most essential results of the experiment is the obtained charge spectrum of GCR nuclei within the range of Z > 40, based on about 11.6 thousand processed tracks. As the result of data processing, 384 nuclei with charges Z ≥ 75 have been identified, including 10 nuclei identified as actinides (90 < Z < 103). Three tracks were identified to be produced by nuclei with charges 113 < Z < 129. Such nuclei may be part of the Island of Stability of transfermium elements.

Results of the model experiment on cosmic muon radiography of a mountain

The results of the model experiment on cosmic muon radiography of a mountain with an object placed in it are presented. Scales of the difference between muon fluxes passed and not passed through the object are shown. The results for objects with densities higher and lower than that of basic ground are compared. The simulation results for the case with two detectors, which allows the determination of the object position in space, are presented. To estimate the degree of the uncertainty associated with muon rescattering in materials, events of muon of passage in iron and ground are simulated in wide energy and length ranges using the GEANT4 package. The results are presented as distributions of the number of events over the final energy and deflection angle as functions of the primary energy and the muon pathlength in a medium.

Search for the νμ→ντ Oscillation with the OPERA Hybrid Detector

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.

Detecting galactic cosmic ray transuranium nuclei in olivine crystals from meteorites

Results from the experimental search for and identification of tracks from the superheavy and transuranium nuclei of galactic cosmic rays in pallacite olivine crystals, conducted as part of project OLIMPIA [1], are presented. To date, 170 crystals from Marjalahti and Eagle Station pallacites have been processed and 6800 tracks corresponding to nuclei with charges Z > 55 have been found; 45 of these are from nuclei with charges of 88 < Z < 92 and three super-long ones were produced by nuclei with Z > 105. The charge of one of these nuclei is estimated in the first approximation as Z = 119(+10,−6). Our data confirm the hypothesis of islands of stability for natural trans-Fermi nuclei.

Calibration measurements of the characteristics of tracks from superheavy nuclei in olivine crystals from meteorites

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.