Studies on Characteristics of UHE Gamma-ray Air Showers and Its Detection Capability

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Simulation code has been constructed taking into account of an interaction between primary gamma-ray and geomagnetic field, and energy spectra of secondary particles (gamma-rays and electrons) at the top of atmosphere have been estimated. Air shower development in the atmosphere initiated by such secondary component (dominantly gamma-rays) has been reconstructed by a summation of sub-showers calculated from AIRES air shower code. LPM effect starts its contribution to the shower development from 10^<19.3>eV and makes shower development to be slower and larger fluctuation with increasing a gamma-ray energy. Hence, interaction cross-section between gamma-ray and geomagnetic field becomes larger from 10^<19.2>eV depending on the geomagnetic field strength and primary energy. Shower development affected by geomagnetic field becomes faster due to the bunch of secondary component with lower energies. The contributions of both effect strongly depend on gamma-ray energy and its arrival direction, and remarkable differences on the shower characteristics could be seen as a function of these parameters. Typically average and individual positions of air shower maximum measured by proposed newly experiments will show clear differences of air shower characteristics between proton and gamma-ray initiated ones, and it will be possible to estimate gamma-ray intensity in an energy region above 10^<19>eV.