Study of the cosmic ray primary spectrum at 1015 < E0 < 1016 eV with the EAS-TOP array

The break observed in the electron shower size power law spectrum of Extensive Air Showers (EAS) at corresponding primary energy E-0 similar to (3 - 5)10(15) eV (&quot;knee&quot;) is studied in different EAS components (electromagnetic and muonic) and at different atmospheric depths. A consistent description is obtained. The interpretation of data in terms of primary composition, and following the most accepted high energy interaction models, leads to an increasing average primary mass in this energy range. The study of such behaviour is expected to provide a crucial information for the understanding of the physical parameters that characterize the break for the different primaries.