A big volume NaI (⌀ 6" x 5") scintillation detector together with a foreseen lightning detector aim to study events of cosmic-ray-triggered electrostatic discharges in the atmosphere. The detector is equipped with lead shielding in order to suppress the Earth component of the natural gamma-ray background and is read out by a 4K spectrometric ADC made by ToIvEl. The amplification is adjusted so that the spectrometer covers energies up to 110MeV. The e+/e- annihilation peak and potassium-40, bismuth-214, thallium-208 peaks are clearly visible on the left side of the shown spectrum and are used to obtain the calibration. The higher energy events are due to cosmic rays. The ambient pressure, humidity, and temperature inside the shielding are also monitored. Test data are being collected for better understanding of the detector stability.