Measurements of the cosmic-ray hydrogen and helium spectra at energies from 20 to 800 TeV are presented. The experiments were performed on a series of twelve balloon flights, including several long duration Australia to South America and Antarctic circumpolar flights. No clear evidence is seen for a spectral break. Both the hydrogen and the helium spectra are consistent with power laws over the entire energy range, with integral spectral indices 1.80 ± 0.04 and 1.68 -->+ 0.04−0.06 for the protons and helium, respectively. The results are fully consistent with expectations based on supernova shock acceleration coupled with a leaky box model of propagation through the Galaxy.

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Cosmic-ray proton and helium spectra: Results from the JACEE Experiment

Detailed experimental information is given for five families of the highest energy range, Σ E γ >1000 TeV. They are named Andromeda, Ursa Maior, M.A.I, M.A.II and M.A.III. Among them, Andromeda, Ursa Maior and M.A.III are observed by a chamber of large thickness and their information both on the electromagnetic and hadronic component is available. All the observed three events are hadron-rich and the energy spectrum of hadrons is harder than that of electrons/gamma-rays. The data is found inconsistent with the hypothesis of proton primary with pion multiple production under the scaling model, after comparison with simulation calculation.

The Highest Energy Events Observed by Chacaltaya Emulsion Chambers

A new method of emulsion chamber analysis by using an image scanner is developed in order to process a large number of X-ray films used in the Tibet hybrid experiment which is carried out to observe primary proton spectrum in the PeV region. The experimental procedure in this method consists of multiple steps of processing the image of the X-ray films, i.e. the detection of cascade showers induced by high-energy γ-rays, the noise reduction, the spatial reconstruction of γ-families and their energy determination. The quality of the results obtained by the new method is compared with that obtained by the current manual method or Monte Carlo simulations. It is shown that sufficiently high quality of the emulsion chamber analysis is realized by the automatic method both in energy and geometrical resolution.

Automatic analysis of the emulsion chamber using the image scanner applied to the Tibet hybrid experiment

Primary proton spectrum around the knee observed by the Tibet air-shower experiment

This article discusses the possibility of screen-type X-ray film for the observation of heavy cosmic-ray primaries. We investigate in detail the optical characteristics of the intensifying screen Gd 2 O 2 S:Tb, and perform a simulation calculation for three-dimensional diffusion of scintillation light emitted from numerous δ-rays (knockon electrons produced by a heavy primary) in the screen. On the basis of these theoretical speculations, we report the experimental results obtained recently by a balloon-borne emulsion chamber with full use of the screen type X-ray film, focusing to the charge resolution of heavy primaries and their flux with energy larger than the rigidity cutoff at Sanriku latitude, E c ∼ 4 GeV/n. All results show that the emulsion chamber with multilayered screen-type X-ray film is quite valid and powerful for the observation of heavy cosmic-ray primaries.

Possibility of screen-type X-ray film for observation of heavy cosmic-ray primaries

Characteristic curves of photographic material used in emulsion chambers

The characteristic features of big family events with ΣEγ≥103 TeV, which were observed with emulsion chambers at Mt. Fuji (3776 m above sea-level), are presented in comparison with the results of the Monte Carlo simulation. Moreover, the behaviour of the halo accompanying big family events is described in connection with that of high-energy gamma-rays incident upon the chamber. On the basis of the experimental data, some inferences about the hadronic interactions at energies around 104 TeV are discussed. The general tendency of our data does not seriously contradict the scaling prediction if the primaries are adequately mixed with heavy nuclei. In this case, the cross-sections should increase rapidly with energy up to 104 TeV at least. There exist no clear signs showing a rapid increase of the average transverse momentum.

Gigantic gamma-ray family events with ΣEγ≥1000 TeV and hadronic interactions

Intensity of Gamma Rays, Hadrons and Families at MT. Fuji

The energy spectra of high energy gamma-rays and hadrons were obtained by the emulsion chamber with 40 c.u. thickness at Mt. Fuji (3750 m). These results are compared with the Monte Carlo calculation based on the same model which is used in a family analysis. Our data are compatible with the model of heavy-enriched primary and scaling in the fragmentation region.

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E. Mikumo

Papers

Characteristic curves of photographic material used in emulsion chambers

Gigantic gamma-ray family events with ΣEγ≥1000 TeV and hadronic interactions

Intensity of Gamma Rays, Hadrons and Families at MT. Fuji

High energy gamma-rays and hadrons at Mount Fuji

Revised Data of Atmospheric High Energy Cosmic-Ray Energy Spectra Obtained at MT. Fuji