  In the framework of the development of the SWGO experiment we have performed
a detailed study of the single unit of an extensive air shower observatory
based on an array of water Cherenkov detectors. Indeed, one of the possible
water Cherenkov detector unit configurations for SWGO consists of tanks, and to
reach a high detection efficiency and discrimination capability between
gamma-ray and hadronic air showers, different tank designs are under
investigation. In this study, we considered double-layer tanks with several
sizes, shapes and number of photo-multiplier tubes (PMTs). Muons, electrons,
and gamma-rays with energies typical of secondary particles in extensive air
showers have been simulated entering the tanks with zenith angles from 0 to 60
degrees. The tank response was evaluated considering the number of
photoelectrons produced by the PMTs, the detection efficiency, and the time
resolution of the measurement of the first photon. This analysis allowed to
compare the performance of tanks with different size, configuration of PMTs,
and with circular, hexagonal and square geometry. The method used and the
results will be discussed in this paper.
