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The nuclear composition of primary cosmic rays is investigated in the energy range 1015–1016 eV. These investigations are performed by comparing the properties of the gamma-hadron families observed by the Pamir and the Pamir-Chacaltaya collaborations with the properties of families generated on the basis of the MC0 quasiscaling model for various nuclear compositions. It is shown that all properties of experimental families are in good agreement with the predictions of the MC0 model for a normal nuclear composition, but that these experimental results are at odds with the results of the calculations that assume a nuclear composition enriched in heavy nuclei.

I. V. AMURINA,1 V. P. ANTONOVA,2 G. M. AUTOVA,3 M. K. BABAEV,4 A. S. BAYGUBEKOV,4 P. F. BEYL’,1 R. U. BEISEMBAEV,1 A. E. BODUNOV-SKVORTSOV,5 A. S. BORISOV,5 K. V. CHERDYNTSEVA,5 A. P. CHUBENKO,5 P. A. CHUBENKO,5 V. G. DENISOVA,5 V. I. DROBZHEV,2 E. N. GUDKOVA,5 A. V. GUREVICH,5 Z. M. GUSEVA,5 E. A. KANEVSKAYA,5 J. KEMPA,6 M. G. KOGAN,5 E. V. KOSTIN,5 O. N. KRYAKUNOVA,2 A. V. KRUGLOV,1 S. V. KRYUKOV,2 M. I. KRYLOWA,1 A. I. KUPCHISHIN,7 A. K. MANAGADZE,8 I. S. MART’YANOV,4 V. M. MAXIMENKO,5 K. M. MUKASHEV,3 R. A. MUKHAMEDSHIN,9 R. A. NAM,1 N. M. NESTEROVA,5 KH. NURITDINOV,10 V. V. OSKOMOV,7 V. P. PAVLYUCHENKO,5 V. V. PISCAL’,1 R. YU. POLYAKOV,1 V. S. PUCHKOV,5 S. E. PYATOVSKY,5 I. V. RAKOBOL’SKAYA,8 T. M. ROGANOVA,8 N. N. ROINISHVILI,11 V. A. RYABOV,5 N. O. SADUEV,7 T. KH. SADYKOV,4 S. B. SHAULOV,5 A. L. SHCHEPETOV,5 S. A. SLAVATINSKY,5 A. V. STEPANOV,1 L. G. SVESHNIKOVA,8 G. T. SHOIYNBAEVA,3 ZH. T. TOLEGEN,7 YU. N. VAVILOV,5 A. V. VARGASOV,5 N. G. VIL’DANOV,1 L. I. VIL’DANOVA,1 V. I. YAKOVLEV,5 T. S. YULDASHBAEV,10 N. N. ZASTROZHNOVA,4 G. T. ZATSEPIN9 and V. V. ZHUKOV1 1Tien Shan Mountain Scientific Station of LPI, Almaty, 480037 Kazakhstan 2Institute of Ionosphere, Ministry of Education and Science, Almaty, 480020 Kazakhstan 3Abai Almaty State University, Almaty, 480100 Kazakhstan 4Physical-Technical Institute of Academy of Sciences of Uzbekistan, Almaty, 700084 Kazakhstan 5P. N. Lebedev Physical Institute, Moscow, 119991 Russia 6Warsaw University of Technology, Warszawska Politechnika, Off-Campus, Plock, 09400 Poland 7Al-Faraby Kazakh National University, Ministry of Education and Science, Almaty, 480012 Kazakhstan 8D. V. Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119899 Russia 9Institute for Nuclear Research, Russian Academy of Sciences, Moscow, 117312 Russia 10Physical-Technical Institute of Academy of Sciences of Uzbekistan, Tashkent, 700084 Uzbekistan 11Institute of Physics Academy of Sciences of the Georgian Republic, Tbilisi, 380077 Georgia

Results of emulsion chamber experiments concerning the properties of multiple particle production at very high energy are discussed in the review, including the cross sections of inelastic and semihard processes, scaling violation in the fragmentation region, average transverse momenta at 1015 eV, exotic events and others.

Chemical composition of PCR were investigated by means of emulsion chambers in several works [1-3]. The conclusion was that the fraction of Fe induced families is less than 3% – 7% and heavy nuclei in primary cosmic rays with energy more than 1016 eV are less than 0.22 – 0.27. The aim of the present report is to show the origin of sensitivity of γ-hadron families to the atomic number of PCR and review once more the conclusion about normal composition of PCR in the energy interval 1015 — 1016 eV.

Factorial moments and fractal dimensions methods are applied to experimental γ -families. Average factorial and fractal characteristics in azimuthal plane are investigated. The results of factorial and fractal study of artificial γ -families, generated by various nuclei, are given as well. The influence of electromagnetic cascade in the atmosphere on structural characteristics of families is analyzed.

The possibilities of investigations of two channels of multiple particle production, an indication of which was found at SPS energies, are discussed in this report.

Inelastic interactions of nuclear-active particles in carbon and iron have been studied using cloud chambers in a magnetic field and an ionization calorimeter at Tskhra-Tskharo Pass at an altitude of 2 500 m above sea level. The installation consists of two cloud chambers 2 × 1 × 0.4 m3 in a magnetic field of 7 000 oersteds and an ionization calorimeter of total thickness about 800 g/cm2. It is triggered when an energy greater than 5 × 1010 eV is released in the ionization calorimeter. The measurements in carbon and iron can be taken simultaneously. Results taken up to the present show that the mean free path for carbon is (96 ± 13) g/cm2 and for iron (130 ± 6) g/cm2.