Speaker
Description
Observations of cosmic gamma rays contribute greatly to cosmic ray physics by elucidating a mechanism of cosmic ray acceleration and identifying gamma-ray sources, but due to the technical difficulties of the measurement method, many parts of this field are less developed than other wavelength. In particular, the polarization of cosmic gamma rays is a physical quantity that can reveal the magnetic field structure of astronomical objects, and is expected to provide a new approach to the radiation mechanism but there are few examples of its observation. The Gamma-Ray Astro-Imager with Nuclear Emulsion (GRAINE) experiment aims to precisely observe cosmic gamma rays with a balloon-borne telescope using nuclear emulsions with excellent spatial resolution. GRAINE can observe cosmic gamma rays with the worlds’ highest resolution by measuring electron pair production originating from cosmic gamma rays in the sub-GeV/GeV energy band and is sensitive to polarization. Polarization measurement requires grain-by-grain analysis in track images at the vicinity of pair-production conversion point, and we are currently developing a precision measurement system using an optical microscope. In this study, we observed Compton-scattered electron tracks due to 6.6 MeV gamma ray beam using nuclear emulsion films and the precision measurement system to verify the ability to measure low-energy electrons, and also to measure the polarization of gamma rays.
