  Although the origin of ultra high energy cosmic rays is still unknown,
significant progress has been achieved in last decades with the construction of
large arrays that are currently taking data. One of the most important pieces
of information comes from the chemical composition of primary particles. It is
well known that the muon content of air showers generated by the interaction of
cosmic rays with the atmosphere is rather sensitive to primary mass. Therefore,
the measurement of the number of muons at ground level is an essential
ingredient to infer the cosmic ray mass composition. In this work we present a
new method for reconstructing the muon lateral distribution function with an
array of segmented counters. The energy range from .4 to 2.5 EeV is considered.
For a triangular array spaced at 750 m we found that 450 m is the optimal
distance to evaluate the number of muons. The corresponding statistical and
systematic uncertainties of the new and of a previous reconstruction methods
are compared. Since the statistical uncertainty of the new reconstruction is
less than in the original one, the power to discriminate between heavy and
light cosmic ray primaries is enhanced. The detector dynamic range is also
extended in the new reconstruction, so events falling closer to a detector can
be included in composition studies.
