## 2 Outlook
The analysis of the atmospheric neutron fluxes obtained from the Excel-Based Program for Calculating Atmospheric Cosmic-Ray Spectrum (EXPACS) shows that the dose deposited by these neutral particles increases with the increase in altitude and latitude, e.g., for an altitude of high mountain (4 km), the dose is increased \(\sim\)19 times; while, for an altitude of commercial flights (10 km), it is increased \(\sim\)156 times. For what concerns the higher energies, the increased dangers related to the augmented penetration power of particles is balanced by the relatively low fluxes. Nevertheless, the nature of these particles is not fully understood, leaving many questions unanswered. In the work reported in [6] by [PERSON], the detection of galactic cosmic rays from ground with air shower arrays up to \(10^{18}\) eV is described. The aim of this paper is to discuss the conflicting results in the \(10^{15}\) eV energy range and the perspectives to clarify the origin of the so-called 'knee' in the all-particle energy spectrum, crucial to give a solid basis for models up to the end of the cosmic ray spectrum. The basic techniques used in reconstructing primary particle characteristics (energy, mass, and arrival direction) from the ground are provided, highlighting why indirect measurements are difficult and results are still conflicting. Entering the topic of the characterization of the indirect detection on ground, three papers propose different techniques for the muon flux analysis. Some new insights on cosmic-ray muons are reported in [7]. In this paper, the authors present some interesting results on these particles registered by a digital gamma-ray spectrometer's active shield, made of five large plastic scintillators. In analogous active shields working in anticoincidence mode with germanium detectors, the generated data are used only as a gating signal and are consequently not stored. However, thanks to digital acquisition applied in designed novel gamma-ray spectrometers, it has become possible to use generated data to reduce the germanium detector background (cosmic rays veto system) and also to initialize long-term monitoring of the muon flux intensity. Fourier analyses also reveal the presence of daily (24 h), near-monthly (27 days) and over bi-monthly (68 days) cycles. Problems of digital processing of Poisson-distributed data time series from various counters of radiation particles, photons, slow neutrons etc. are relevant for experimental physics and measuring technology. In [8] a low-pass filtering method for normalized Poisson-distributed data time series is proposed and a digital quasi-Gaussian filter with a finite impulse response is designed. Moreover, the results of testing such filtering method on model and experimental Poisson data from the UMAGAN muon hodoscope, are presented. Finally, the Cosmic-Ray Extremely Distributed Observatory (CREDO) project--established to detect ultra high-energy cosmic ray particles--is described in [9]. Among other and more conventional detection techniques, it makes also use of cameras in smartphones as particle detectors, creating a extremely innovative and highly educational method of experimental observations. In this paper the search for cosmic-ray muons, recorded using this method, is presented. This research received no external funding. The authors declare no conflict of interest.