PoS - Proceedings of Science
Volume 444 - 38th International Cosmic Ray Conference (ICRC2023) - Gamma-ray Astronomy (GA)
Gamma-Ray Astro Imager with Nuclear Emulsion, Evaluation for timestamper emulsion film for the balloon experiment
S. Nagahara
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Pre-published on: August 17, 2023
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We are developing the GRAINE (Gamma-Ray Astro Imager with Nuclear Emulsion) project for precise (0.08 degree @ 1 - 2 GeV) and large-aperture-area observations of cosmic gamma rays in the 10 MeV - 100 GeV by long balloon flights of the nuclear emulsion telescope. We have demonstrated the performance and feasibility of balloon-borne emulsion gamma-ray telescope experiments in 2011, 2015, and 2018. We succeeded in imaging the Vela pulsar at high resolution during our 2018 observations. We are preparing for observations in spring 2023 with an aperture area of 2.5 m^2, 7.5 times larger than in 2018. Since emulsion films have no time-resolution, time information is added using a mechanism called a timestamper. For the emulsion films used in this part, a new type of film suitable for large-scale production was adopted. In this study, the basic performance and long-term properties of this film were evaluated for suitability for the GRAINE experiment. First, we evaluated the sensitivity and noise level by using films cut to several centimeters and preparing samples under different conditions that affect film quality (humidity during vacuum packing, temperature during storage, and storage period). Next, we evaluated the sensitivity of the 10 cm x 12.5 cm films by scanning the tracks with the Hyper Track Selector. These evaluation results and the latest status of the films used in the balloon-borne experiment are presented.
DOI: https://doi.org/10.22323/1.444.0825
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