Photometric Method in Energy Determination of Cosmic-Ray Showers in Emulsion Chamber

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Since Japan-Brazil Emulsion Chamber Collaboration started in 1962 on Mt. Chacaltaya, X-ray films have been used together with nuclear emulsion plates for detection of the high energy cosmic-ray showers. Meanwhile, many members, Japanese and Brazilians, of this collaboration have made various attempts to use X-ray film for energy determination as well as for detection. The present work is developed in this basis. Application of the photometric method with X-ray films for energy determination of high energy electron showers gives us the following advantages. Firstly, signal to noise ratio of shower spot on X-ray film is much higher than that on nuclear emulsion plate, because of high sensitivity of X-ray films. Secondly, measurement of spot darkness of shower using micro-densitometer is more facile and more rapid, as compared with counting of electron tracks of the shower in nuclear emulsion plates. Consequently, the photometric method with X-ray film enabled us to make a scale-up of emulsion chamber with great stride. Photometric measurement and track counting method are applied simultaneously to each of 47 showers and the correspondence between spot darkness, D_<max>, and shower energy, E_0, is established empirically. The relation is also calculated with three-dimensional shower theory. Both results agree well and give the relation D_<max>∝E^<0.85>_ο for various energies. The method of energy determination for localized nuclear interaction in the chamber itself-Pb-jet shower-is also established empirically and theoretically. The same method as for electron shower is valid for Pb-jet showers with energy ΣE_γ≲1 TeV, if one uses slit larger than 150 μm radius in micro-densitometer.
理論物理学刊行会の論文
1971-09-14

Photometric Method in Energy Determination of Cosmic-Ray Showers in Emulsion Chamber

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