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