K. Ozaki

Development of new-type nuclear emulsion for a balloon-borne emulsion gamma-ray telescope experiment

This study reports a new-type of nuclear emulsion that improves the track-finding efficiency of charged particle detection. The emulsion is applied to the GRAINE project, a balloon-borne experiment that observes cosmic γ-rays through an emulsion γ-ray telescope. The new emulsion film dramatically improves the detection efficiency for γ-rays. The nuclear emulsion gel and films for the second GRAINE balloon-borne experiment (GRAINE-2015) were fully self-produced by ourselves. New handling methods for the novel emulsion film have also been developed. Over time, the stored films gradually become desensitized to minimum ionizing particles, but the original sensitivity can be restored by a resetting process. Moreover, the fading of latent images can be arrested by a drying process. To sensitize the new-type films and avoid their fading, emulsion preprocessing was applied immediately prior to GRAINE-2015. A balloon flight with the emulsion γ-ray telescope was successfully completed in Australia on 12th May 2015. By scanning with automated optical microscopes and analyzing the penetrated tracks, we confirmed the high track-finding efficiency (97%) of the mounted films. The analysis of γ-ray event detection, aims at detecting Vela pulsar, is in progress.

First demonstration of gamma-ray imaging using a balloon-borne emulsion telescope

We promote the precise gamma-ray observation project Gamma-Ray Astro-Imager with Nuclear Emulsion (GRAINE), which uses balloon-borne emulsion gamma-ray telescopes. The emulsion telescope realizes observations with high angular resolution, polarization sensitivity, and large aperture area in the 0.01--100 GeV energy region. Herein, we report the data analysis of emulsion tracks and the first demonstration of gamma-ray imaging via an emulsion telescope by using the flight data from the balloon experiment performed in 2015 (GRAINE 2015). The emulsion films were scanned by the latest read-out system for a total area of 41 m

Measurement of Cosmic Ray Nuclei with GRAINE2015

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

in three months, and then the gamma-ray event selection was automatically processed. Millions of electron-pair events are accumulated in the balloon-borne emulsion telescope. The emulsion telescope detected signals from a calibration source (gamma rays from the interaction of cosmic rays with an aluminum plate) with a high significance during the balloon observation and created a gamma-ray image consistent with the source size and the expected angular resolution in the energy range of 100--300 MeV. The flight performance obtained in the GRAINE 2015 experiment proves that balloon-borne emulsion telescope experiments with larger area are feasible while maintaining expected imaging performance.

Multi-stage shifter for subsecond time resolution of emulsion gamma-ray telescopes

GRAINE(Gamma Ray Astro-Imager with Nuclear Emulsion) experiment consists of a balloon borne emulsion chamber and emulsion film shifting system launched on May 6, 2015 in Australia and its acceptance and flight duration is 3780m

Demonstration of polarization sensitivity of emulsion-based pair conversion telescope for cosmic gamma-ray polarimetry

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GRAINE 2015, a balloon-borne emulsion

sr and 14 hours at 37 km above sea level, respectively. The main scientific goals of GRAINE2015 are the precise measurement of sub GeV gamma-rays from Vela pulsar, the measurement of charm particle production cross section at high altitude in the air and the study of cosmic ray nuclei compositions. The nuclear emulsion films used in GRAINE2015 will be able to measure cosmic ray nuclei from hydrogen nuclei to more than iron nuclei. The measurement of the chemical composition of cosmic ray nuclei in the MeV-TeV energy range will reveal new insights about the cosmic ray nuclei life in the our galaxy, from their origin to the propagation in the interstellar medium. The Cosmic ray nuclei absolute charge Z is measured along the trajectory in the GRAINE2015 emulsion films by using high speed emulsion track selector (HTS). This allows to scan the entire emulsion film within the zenith angle less than 63 degree. The charge measurement methods in HTS scan data are here explained, and their performance presented.