Studies of the knee of the cosmic rays primary spectrum through measurements in the 1016–1018 eV energy range

In this contribution I review the most recent results obtained by experiments studying the primary cosmic rays spectrum at energies around the knee, i.e. the change of slope observed at Eknee∼3×1015eV.The main results are: the change of slope has been observed in the spectra of all secondary components of extensive air showers. The primary chemical composition gets heavier above the knee. Almost all experiments, with the exception of TIBET ASγASγ, attribute the change of slope to the light component of cosmic rays. The arrival directions of cosmic rays are highly isotropic.These results favor an astrophysical explanation of the knee either as the maximum energy achievable in galactic sources or of end of the containment inside galactic magnetic fields. Nevertheless the scenario is neither complete nor univocally accepted and relevant informations can be obtained studying the 1016–1018 eV energy range.