Observation of fluctuation of gamma-ray count rate accompanying thunderstorm activity and energy spectrum of gamma rays in the atmosphere up to several kilometers altitude from the ground

Tatsuo Torii, JAEA Japan Atomic Energy Agency, Remote Sensing Div., CLADS, Nucl. Sci. Res. Inst., Tokai-mura, Japan, Yukihisa Sanada, JAEA Japan Atomic Energy Agency, Fukushima Environmental Center, Minamisouma, Japan and Akira Watanabe, Fukushima University, Faculty of Symbiotic Systems Science, Fukushima, Japan