Study of the cosmic ray primary spectrum at 10(15)< E-0 < 10(16) eV with the EAS-TOP array

The break observed in the electron shower size power law spectrum of Extens ive Air Showers (EAS) at corresponding primary energy E-0 similar to (3 - 5 )10(15) eV ("knee") 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, an d following the most accepted high energy interaction models, leads to an i ncreasing average primary mass in this energy range. The study of such beha viour is expected to provide a crucial information for the understanding of the physical parameters that characterize the break for the different prim aries.