Misurazione delle componenti pesante e leggera dello spettro primario dei raggi cosmici nel range energetico 10^(16)-10^(18) eV con l'esperimento KASCADE-Grande.

One of the most interesting questions concerning the cosmic ray physics is the one connected to the change of slope in the primary cosmic ray energy spectrum. The cosmic ray (CR) flux, as a function of the energy, follows a power law function: E^(-gamma) where gamma assumes a constant value equal to 2.7. At energies around 3*10^(15) eV, however, the spectrum's slope changes becoming steeper and gamma turns to 3.1. This change in the slope of the spectrum is known as the knee of cosmic rays. The origins of this knee are, at present, unknown. Several hypothesis and theories, however, have been expressed about it. The experimental results achieved in the last decade, especially by the EAS-TOP and KASCADE experiments, showed that the change of slope observed at E=3*10^(15) eV is due to the light component (H and He) of primary cosmic rays. At present, however, the same feature, forecast at an energy of E=10^(17) eV, has not been observed for the heavy component (Fe). The KASCADE-Grande experiment, as an extension of the KASCADE experiment, was built with the definite purpose to study the spectrum's behavior in the energy range around which the knee of the heavy component is expected (10^(16)-10^(18) eV). The aim of this thesis work is to analyze, using the data of the KASCADE-Grande experiment, the behavior of Extensive Air Showers on the basis of the ratio between the number of muons and charged particles at observation level. This ratio provides an evaluation of the mass of the particle which originated the shower, allowing the distinction between the light (H) and heavy (Fe) components of primary CRs. In this way it is possible to study the two components' spectra thus verifying the existence (or non existence) of the heavy component's knee.