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The change in the fluxes of the lightest and heaviest nuclei in the mass composition of primary cosmic radiation in the energy range of E0 = 1-100 PeV is analyzed on the basis of data from the KASCADE-Grande experiment. This analysis is performed by means of the min-max age (Smin-max) method for extensive air showers (EAS) that is proposed in the present article. This method makes it possible to estimate the exponents of the spectra for the lightest and heaviest nuclei in the mass composition of primary cosmic radiation and to study irregularities in these spectra at energies E0 in the range under consideration. The Smin-max method for estimating the mass composition of primary cosmic radiation is based on a sizable sample (more than 100 million events) of data on EAS features in the range of E0 = 1-100 PeV from the KASCADE-Grande experiment. It is shown that, in the primary-energy range of E0 = 1-100 PeV, the exponent in the integrated spectrum changes from 2.1 to 2.7 for the lightest nuclei in the mass composition of primary cosmic radiation and from 1.5 to 2.1 for the heaviest nuclei. These results comply with the conclusion drawn by the KASCADE-Grande Collaboration that the knee in the E0 spectrum of nuclei of primary cosmic radiation in the range of E0 = 3-5 PeV is due to the elimination of light nuclei. The bump appearing in the E0 spectrum of primary cosmic radiation according to the database of the KASCADE-Grande experiment and lying in the range of E0 = 50-75 PeV is analyzed by the Smin-max method and is found to agree with data of the GAMMA (GAMMA-07) experiment.

We present a description of the new complex installation for the study of extensive air showers which was created at the Tien Shan mountain cosmic ray station, as well as the results of the test measurements made there in 2014-2016. At present, the system for registration of electromagnetic shower component consists of $\sim$100 detector points built on the basis of plastic scintillator plates with the sensitive area of 0.25m$^2$ and 1m$^2$, spread equidistantly over $\sim$10$^4$m$^2$ space. The dynamic range of scintillation amplitude measurements is currently about $(3-7)\cdot 10^4$, and there is a prospect of it being extended up to $\sim$10$^6$. The direction of shower arrival is defined by signal delays from a number of the scintillators placed cross-wise at the periphery of the detector system. For the investigation of nuclear active shower components there was created a multi-tier 55m$^2$ ionization-neutron calorimeter with a sum absorber thickness of $\sim$1000g/cm$^2$, typical spatial resolution of the order of 10cm, and dynamic range of ionization measurement channel about $\sim$10$^5$. Also, the use of saturation-free neutron detectors is anticipated for registration of the high- and low-energy hadron components in the region of shower core. A complex of underground detectors is designed for the study of muonic and penetrative nuclear-active components of the shower. The full stack of data acquisition, detector calibration, and shower parameters restoration procedures are now completed, and the newly obtained shower size spectrum and lateral distribution of shower particles occur in agreement with conventional data. Future studies in the field of $10^{14}-10^{17}$eV cosmic ray physics to be held at the new shower installation are discussed., Comment: 32 pages, 20 figures. Submitted to Nucl. Instrum. Methods A

The phenomenon of gamma-ray families featuring halos that is observed in an experiment with x-ray emulsion chambers (XREC) in the Pamir experiment and in other XREC experiments is explained. The experimental properties of halos are analyzed via a comparison with the results of their simulation. It is shown that gamma-ray families featuring halos are predominantly produced (more than 96 % of them) by protons and heliumnuclei. This makes it possible to employ the experimental properties of halos to estimate the fraction of protons and helium nuclei in the mass composition of primary cosmic radiation.

In the energy range above the PCR "knee" (5-1000 PeV), the emulsion chamber data exhibit some new features which are hard to explain in the framework of the Standard Model. In this survey the results of a systematic quest of some new and exotic types of events which are observed in the Pamir emulsion chamber experiment are presented, namely, huge "halo" events, coplanar events, penetrating hadrons with abnormally weak absorption in lead, "Centauro"-type events. Possible theoretical approaches for their explanation are discussed.

The fraction of halo events among gamma-hadron families with SUM(Egamma) > 500 TeV is analyzed. The comparison of experimental data and Monte-Carlo simulations by MC0 code of quark-gluon string model under various assumptions on the PCR mass composition suggests a slowly increasing contribution of nuclei heavier than protons and alpha-particles to PCR mass composition. Effective atomic number of PCR particles changes in the energy interval 10^15-10^17 eV so that lnA grows from 2 to 2.5.

Adjusted data on the fraction of protons in the mass composition of primary cosmic rays (PCRs) in the energy range of 10^15-10^17 eV are presented. Adjustments are made according to detailed calculations of the response of the X-ray emulsion chamber in the PAMIR experiment. It is demonstrated that the fraction of protons in a PCR is 16-18% for E0 = 10^15-10^16 eV and does not change within the error for E0 = 10^16-10^17 eV.

The experimental gamma-families in which events called "halos" were detected using X-ray emulsion chambers (XRECs) of the PAMIR experiment are described. The halo nature is explained within the standard model of nuclear interactions. Based on events with halo, the fraction of p+He in primary cosmic rays (PCR) was estimated. It is shown that the PCR mass composition remains mixed in the range E0 = 1-100 PeV.

Recently essential efforts were made to improve measurement routine with X-ray films exposed in the X-ray emulsion chambers at the Pamirs. Analysis of X-ray emulsion response upon recorded events show that gamma-family energy and intensity in early publications were over estimated. The main physical results of the new analysis are presented.

The investigation of hadron-nuclear interactions in Pamir experiment is carried out by means of X-ray emulsion chambers of two types: carbon (C) and lead (Pb). While comparing the results from the chambers of both types it was found a discrepancy in n sub h and E sub h(1)R values. The observed discrepancy in C and Pb chambers is connected with the difference in values of effective coefficients of energy transfer to the soft component K sub eff for C and Pb chambers.