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

Abstract

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 balloonborne 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 selfproduced 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 trackfinding efficiency (97%) of the mounted films. The analysis of γ-ray event detection, aims at detecting Vela pulsar, is in progress. K: Particle tracking detectors (Solid-state detectors); Gamma telescopes 1Corresponding author.

GRAINE balloon experiment in 2015

“…The track-finding efficiency of HTS was higher than 95% at tan θ < 2.0 angular region as a result of evaluating the filling rate of tracks penetrating multiple films [12]. Figure 4.…”

Ultra fast nuclear emulsion readout system HTS

“…We evaluated base track finding efficiency and angular accuracy by using a nuclear emulsion films used for GRAINE 2015 flight [4]. The track finding efficiency was defined as the proportion of the number of tracks found in a certain film to the number of tracks that could be connected by the next film.…”

Latest nuclear emulsion technology

“…Figure 6 shows the trackfinding efficiency obtained by the high-sensitive film and HTS. At each incident angle from tan θ = 0.0 (a vertical angle) to tan θ = 2.0, more than 95% was evaluated [9].…”