GRAINE project: The first balloon-borne, emulsion gamma-ray telescope experiment

salman syed ali;

The GRAINE project (Gamma-Ray Astro-Imager with Nuclear Emulsion) has been developed for the observation of cosmic γ -rays in the energy range 10MeV–100 GeV with a precise (0.08◦ at 1–2 GeV), polarization-sensitive, large-aperture-area (∼10m2) emulsion telescope by
repeated long-duration balloon flights. In 2011, the first balloon-borne experiment was successfully performed with a 12.5 × 10 cm2 aperture area and 4.6 hour flight duration for a feasibility and performance test. Systematic detection, energy reconstruction, and timestamping of γ -ray eventswere performed across thewhole area of the emulsion film, up to 45◦ incident zenith angle, down to 50MeV γ -ray energy, with 97% detection reliability, 0.2 sec timestamp accuracy, and
98% timestamp reliability. A γ -ray data checking and calibration method was created using the γ -rays produced in the converter. We measured the atmospheric γ -ray flux in the energy range 50–300MeV and obtained a first understanding of the cosmic γ -ray background. By combining the attitude data, we established a procedure for determining the γ -ray arrival direction in celestial coordinates. The first flight of the balloon-borne emulsion telescope confirmed its potential as a high-performance cosmic γ -ray detector.