Atmospheric Gamma-Ray Observation Over 100gev With Ppb-Bets By Long Duration Balloon Flight In Antarctica

Since atmospheric gamma rays at high altitude are mainly produced by a single interaction of primary cosmic rays with atmospheric nuclei, they are very useful to study nuclear interaction models and atmospheric neutrinos. We have observed atmospheric gamma rays from 100 GeV to 1 TeV with PPB-BETS by a long duration balloon flight of Polar Patrol Balloon (PPB) in Antarctica. The observation was carried out for 13 days at an altitude of similar to 35 km in January 2004. The detector of PPB-BETS is an imaging calorimeter composed of scintillating-fiber belts and plastic scintillators inserted between lead plates. We have collected 5.7 x 10(3) events over 100 GeV. The number of observed atmospheric gamma rays is 1.0 X 10(2) events in the energy range of 100 GeV to 1 TeV.