The characteristics of Fuji Nuclear Emulsion Type ET-7A have been investigated. The exposure of emulsions was carried out at sea level, the top of Mt. Fuji and free balloon of 30, 000 meters height. After the exposure, the emulsions were developed by the amidolbisulphite temperature method or by the metol-hydroquinone two bath method. The dependence of the sensitivity of emulsions on the temperature of development and on the development time is investigated.
The results showed that the tracks of minimum ionization particle are clearly visible. The blob density of the plateau ionizing particles (electrons of μ-e decay and of cascade shower) is 25-40 blobs/100 microns, the fog grains in the processed emulsion is 0.1-5.0/1, 000 cubic microns, and the grain size distribution in the tracks of the plateau ionizing particle is nearly to Ilford G.5 emulsion.

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