H. Semba

Observation of a high-energy cosmic-ray family caused by a Centauro-type nuclear interaction in the joint emulsion chamber experiment at the Pamirs

Abstract An exotic cosmic-ray family event is observed in the large emulsion chamber exposed by the joint at the Pamirs (4360 m above sea level). The family is composed of 120 γ -ray-induced showers and 37 hadron-induced showers with individual visible energy exceeding 1 TeV. The decisive feature of the event is the hadron dominance: ΣE γ , ΣE ( γ ) h , 〈 E γ , 〈 E ( γ ) h 〉, 〈 E γ · R γ 〉 and 〈 E ( γ ) · R h 〉 being 298 TeV, 476 TeV, 2.5 TeV, 12.9 TeV, 28.6 GeV m and 173 GeV m, respectively. Most probably the event is due to a Centauro interaction, which occured in the atmosphere at ∼700 m above the chamber. The event will constitute the second beautiful candidate for a Centauro observed at the Pamirs.

Energy determination of the cascade shower by means of a new type of emulsion chamber with diffuser module

Abstract An account is given of a new type of emulsion chambers which have been in our use since 1997 in our RUNJOB program (RUssia–Nippon JOint Balloon-program). Each chamber is equipped with an additional “diffuser module” placed under the usual set of modules. We have made the experiments using 4 cm thick diffuser modules composed of several photo-sensitive layers (X-ray films and/or nuclear emulsion plates) sandwiched with spacers. The result is as follows. Even in the case where the path length of only 6 radiation lengths is available within the calorimeter module placed above, the visible energy sum is determined with an accuracy better than σ∼0.2 for a group of electromagnetic cascade showers induced by a proton of energy up to several tens of TeV, or by an iron nucleus of energy up to one hundred TeV. If the available path length in the calorimeter module is 9 radiation lengths, we can estimate the energy sum up to ∼100 TeV within an accuracy of σ∼0.2 for a proton-induced cascade shower group. It means that the use of our new-type emulsion chamber can reduce the detector payload dramatically, which is essentially important for the high-energy cosmic-ray observations made on board the vehicles such as balloons, satellites and so on.

First results obtained by RUNJOB campaign

Abstract We report experimental results obtained by using a wide-gap type emulsion chamber flown in the first Japanese-Russo joint balloon project, called RUNJOB ( RU ssia- N ippon JO int B alloon-program). Two balloons were launched from Kamchatka in July 1995, and both were recovered successfully near the Volga River. The exposure time was 130 hours for the first flight and 168 hours for the second. The mean ceiling altitude, in both flights, was 32 km corresponding to 10 g/cm 2 . Total area of the emulsion chamber was 0.8 m 2 , and the thickness 0.385 and 2.28 collision m.f.p.s for vertically incident proton- and iron-primaries, respectively. We detected 381 showers using Fuji-#200-type X-ray film; of these 174 showers were due to atmospheric secondary γ-rays, and the rest 207 came from nuclear components. The energy range covers 20∼200 TeV for proton-primary, 3∼30 TeV/nucleon for helium-primary, and 0.7∼5 TeV/nucleon for iron-primary. We give the energy spectra for various elements (proton, helium, …, iron) as well as the all-particle spectrum and the average mass of the cosmic-ray primaries.

High-Energy Gamma Rays in the RUNJOB Experiment

The latest results of studies of the gamma-ray spectra recorded together with charged particles in the Russian-Nippon Joint Balloon (RUNJOB) experiment are presented. A comparison of the experimental spectra with the results of the calculations based on assumptions of different intensities of the gamma-ray spectra demonstrates that the previously published intensities of primary cosmic rays measured in the RUNJOB experiments are underestimated.