Measurement of the energy of γ-ray shower with x-ray films, 2

For the studies on high energy cosmic ray particles, X-ray film type emulsion cloud chambers have begun to be used for energy measurement, using X-ray films and photoelectric density meters. Cosmic ray study group of Yamanashi University has carried out the experiment on cosmic ray air shower by combining an image intensifier system and X-ray films. The X-ray film type ECC for the measurement of incident particle energy is placed on the detector of the core of air shower in the experimental apparatus. The incident energy and incident angle of γ-ray shower were analyzed from the density of films with a photoelectric density meter. Also energy distribution and the attenuation mean free path of γ-ray were analyzed. The area of the ECC was 2.25 m2, and it was exposed for 580 hours at Norikura cosmic ray observation station. The ECC consisted of an uppermost lead plate of 3 cm thick, 4 X-ray films and lead plates of 1 cm thick piled up alternately, and a lowermost plastic scintillator. 27 cases of shower were caught with the X-ray films. The energy of 14 cases among them was determined by measuring the blackening density due to the shower. The energy of incident particles distributed in the range of 0.5--4 TeV, but mostly around 1 TeV. Average pass distance through lead was 9,6 Cu. The relation between energy and maximum density is represented by the empirical formula E asymptotically equals 12.11 Dsub(max) - 0.56. The energy measurement with X-ray film type ECC is possible if high accuracy is not required. (Kako, I.)