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An experiment for measuring the flux of cosmic diffuse gamma rays with energies above 100 TeV (the Carpet-3 air shower array) is now being prepared at the Baksan Neutrino Observatory, Institute for Nuclear Research, Russian Academy of Sciences. The preparations entail a substantial increase of the areas of both the muon detector and the surface air shower array. The experiment’s sensitivity to showers generated by primary gamma rays is estimated for different configurations of the array. In addition, preliminary estimates of the upper limit on the flux of diffuse gamma rays with energies higher than 1.3 PeV, derived using experimental data from the old Carpet-2 array, are presented for a net exposure time of 9.2 years.

A way of estimating a muon-enduced neutron flux has been proposed. The technique is used to estimate the neutron background at the Baksan Underground Scintillation Telescope (BUST). A two-pulse signature (unstable 12B production and its subsequent decay) is used to identify neutron events. The integrated average neutron flux on the external planes of detector is an order of magnitude higher than the one on the internal planes. Within the limits of statistical error, the resulting neutron flux agrees with predictions from simulations for the depth at which the BUST lies using the FLUKA program.

The results from a 29-month investigation into the EAS electromagnetic component using the PRISMA-32 array are presented, notably for the central density spectrum and energy deposit spectrum. The array consists of 32 en-detectors in which specialized inorganic scintillators (SL6-5 phosphorus composition) based on silver-activated zinc sulfide (ZnS) with LiF enriched to 90% 6Li (ZnS(Ag) + 6LiF) are used as detecting layers. The possibility of detecting the electromagnetic component using a thin scintillation neutron detector with the multiple passage of charged particles is shown. The experimental data are compared to the results from simulations.

The current status of the experiment on recording neutrino bursts from core collapse stars is presented. The actual observational time T (from June 30, 1980 until December 31, 2009) is 25.58 years. An upper bound of the mean frequency of gravitational collapse in our Galaxy fcol < 0.090 year−1 at a 90% confidence level. The results of studying single events at the facility in the case of muon inelastic interaction of cosmic rays with the matter of the detector are presented.

Characteristics of the hadronic component of exstensive air shower (EAS) trunks are investigated at the CARPET-2 array of the Baksan Neutrino Observatory, Institute for Nuclear Research, Russian Academy of Sciences. In this work, we study showers with axes that located within its muon detector (MD). We discuss the procedure for selecting such showers in our experiment. The relationship between the number of thermal neutrons detected by heat detectors installed in the muon detector’s tunnel and the total energy of a cascade generated by hadrons in the magnetic detector’s absorbent matter is presented.

The first results of measurements of the thermal-neutron flux in extensive air showers (EASs) using an unshielded scintillation thermal-neutron detector in the Multicom prototype array at the Baksan Neutrino Observatory of the Institute for Nuclear Research are reported. The operating capacity of the new method for studying the EAS hadron component via detection of thermal neutrons and good prospects of this method are demonstrated.

A new data acquisition system that makes it possible to measure the count rate of each detector of the Andyrchi air shower array every millisecond is described. This new detection system allows us to search for ultrashort bursts of cosmic ray intensity when operating the array in the single-component detection mode. The method of data acquisition and analysis is discussed.

The prototype of a novel type EAS (extensive air shower) recording and investigation array (the PRISMA project) is created on the basis of the NEVOD experimental complex through cooperation between Institute for Nuclear Research, Russian Academy of Sciences, and the National Research Nuclear University MEPhI. The prototype (ProtoPRISMA) consists of thirty-two en-detectors sensitive to EAS electromagnetic (e) and hadronic (via the registration of thermal neutrons) (n) components. The array is designed to develop and to test a new method of EAS investigation using neutron and electromagnetic components and to obtain preliminary data on the spectrum and composition of cosmic rays.

An innovative method for studying the properties of extensive air showers (EASes) that is based on the detection of thermal neutrons generated by high energy hadrons under a soil absorber of 500 g cm−2 is proposed and tested. It is shown that underground hadronic calorimeter can be performed with special scintillation detectors developed by the authors. The method could be quite useful in gamma shower selection and investigations of EAS properties, primary cosmic ray mass composition, EAS core location, and so on.

The first experimental data on detection of thermal neutrons accompanying extensive air showers (EASs) which were obtained at two prototypes of the future novel PRISMA EAS array are reported. The operation of this array (even in the minimum prototype version) and its ability to yield completely new information on the hadron and electron components of the EAS were experimentally checked.

The first results obtained during one year of measurements at the upgraded shower Carpet-2 installation at the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences, are presented. The results of calculation of the energy response of the installation are given. The results of data analysis using the standard method and the East-West method are compared. The constraints on amplitudes of harmonics of solar anisotropy for three values of primary energy: E > 12 TeV, E > 40 TeV, and E > 70 TeV, are obtained.

The state of the art and the project of modernization of the extensive-air-shower array Carpet-2 of the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences are described. The modernized array will allow the performance of detailed study of variations in the cosmic ray intensity, the energy spectra and composition of primary cosmic rays in the energy range 1013–1016 eV, and the anisotropy of primary cosmic rays with energies above 1013 eV.

Search for neutrino bursts from collapsing stars with the Baksan underground scintillation telescope has been carried out since 1980. In this study, the experimental data obtained during the period from 2001 to 2005 inclusive are analyzed. The upper limit of the mean frequency of collapses in the Galaxy over the entire period of observations (the total live time is 21.83 yr) was found to be 0.105 yr−1.