## 2 The Archaeological Site Probing by Muon Radiography Method  
High-energy muons generated in the Earth atmosphere by the cosmic ray particles have a very high penetrability, making them unique agents for probing sizable objects under the earth and on its surface (geological deposits, volcanoes, caves, nuclear reactors, archaeological objects etc.). Even at comparatively limited energy, a muon can pass through the entire atmosphere and penetrate deep into the earth's crust: cosmic muons with energies of E\(\mu\sim\) 1-10 TeV were registered in underground laboratories at depths of about 2 km [10]. As a result, since the spectrum of atmospheric muons of cosmic origin extends to hundreds of TeV and above, muon fluxes have in their composition high-energy particles that can pass through kilometer-thick objects of high density. The physical principle of muon radiography is based on two phenomena, the first of which is the attenuation of the muon flux in the absorber owing to electromagnetic processes (ionization, bremsstrahlung radiation, generation of electron-positron pairs). When a substance of another density occurs during a charged particle flux, the intensity of electromagnetic interactions changes and affects the intensity of muon flux absorption in this zone. The other phenomenon is conditioned by multiple Coulomb scattering, when with the increase of the absorber atomic number, the extent of particle scattering increases to lead to a noticeable deviation of the particle trajectory angle from the initial one. Currently, in experiments conducted using the method of muon radiography, both electronic and emulsion track detectors are used. Emulsion detectors [11; 12] have a number of advantages, with the main one being a high angular resolution. Of all the muon radiography detectors, the emulsion ones have the best angular resolution. None of the currently known detectors of elementary particles provide a spatial resolution in the way that the nuclear emulsion does: with a grain size of 0.3-1 micron, the grain deviation from the restored trajectory of the particle does not exceed the average value of 0.8 microns, and under certain conditions can reach 0.2 microns. When using natural probing radiation, that is the flux of atmospheric muons, the detector is placed on a side or below the studied object (the so-called one-sided muon radiography [13]). The number of muons passing through the object depends on material of the object under study and the length of the muon path within it. Muons with a range in the substance greater than their path lengths in the tested object reach the detector. The registered particle tracks, which are chains of developed grains of silver halides ionized by a passing charged particle, allow restoring the spatial trajectory of this particle with accuracy of several milliradians (which means a spatial resolution about 10 m at the distance of 1 km). Each registered muon is characterized by the values of azimuth and zenith angles of its trajectory relative to the axis normal to the detector plane. The angular distributions of muon tracks registered by the detector aimed at the object indicate absorption and scattering features of these probing particles and, therefore, the presence in this area of zones with different material properties. The use of several detectors enables obtaining a 3D tomogram of the internal structure of the object under study. Detailed review of the method and its potential are given in Reference [14]. Preliminary analysis carried out on topographical maps has shown that muon radiography detectors can be arranged inside the object so that to scan it completely (Figure 2). Registration of muons in solid angles indicated in Figure 2 was carried out by track detectors, made of layers of double-sided nuclear emulsion films of 10 \(\times\) 12.5 cm\({}^{2}\)[15; 16]. In total, five emulsion detectors were used in this experiment: four wall-oriented detectors, and one directed upwards to measure the vertical muon flux.