Y. Hatano

Energy Spectrum of Primary Cosmic Rays Between 10**14.5-ev and 10**18-ev

Size spectra of electrons (Ne) and muons (Nmu ) are obtained from the Akeno extensive air-shower experiment. The primary spectrum estimated from each spectrum is the same and is expressed by J(E0)dE0(4.0-5.0)*10-23(E0/1015.67)- gamma dE0 m-2 s-1 sr-1 where gamma =2.62+or-0.12 below and gamma =3.02+or-0.05 above 1015.67 eV. There is no other significant change of slope in either the electron or the muon size spectrum beyond the corresponding energy 1015.67 eV.

Anisotropy of the arrival direction of extensive air showers observed at Akeno

The anisotropy of the arrival direction of the primary cosmic ray of energy 1015 to 1018 eV is studied using approximately 300000 showers observed in 1981 and 1982 at the EAS array at Akeno. The anisotropy of the second harmonics appears to be (1.1+or-0.4)% in the region 1016 to 1017 eV. The showers with rich muon content seem to come preferentially from a direction of about 230 degrees in the right ascension. No statistically meaningful anisotropy is found for muon-poor showers.

Expanded Array for Giant Air Shower Observation at Akeno

Abstract As the first stage of a future huge air shower array, the Akeno array was expanded to about 20 km2 by adding 19 scintillation counters of 2.25 m2 area outside the present 1 km2 array and installing a new data collection system. These detectors are connected successively by two optical fiber cables. The total number of electrons and the arrival direction of extensive air showers of 1010 GeV can be determined with accuracies of 25% and 3° respectively with this array. The present recording system is applicable to other experiments in which many sensors are connected in sequence.

The Lateral Distribution of Electrons of Extensive Air Shower Observed at Akeno (920 g/cm2)

Lateral distribution of electrons is determined with scintillators of 50 and 3 mm thickness from the core to 500 m in the Akeno array. Lateral distribution can not be represented by the NKG function with a single age parameter. From size and depth dependence of age parameter and its fluctuation at fixed muon size, elongation rate and fluctuations in the depth of shower maximum are estimated and discussed.

A new method of ionization-neutron calorimeter for direct investigation of high-energy electrons and primary nuclei of cosmic-rays up to the “knee” region

Abstract A new technique of the Ionization Neutron Calorimeter (INCA) to be installed aboard a satellite or a space station is capable of opening new horizons for cosmic-ray physics. The main goal of the experiment proposed is studying local nearby sources of high-energy cosmic rays by measuring the spectrum and composition of the nuclear component with the energy resolution of better than 30% that is sufficient for solution of these problems in the energy range 0.1–10 PeV, i.e., in the so-called “knee” region, and the spectrum of primary electrons in the energy range 0.1–10 TeV with the proton-background suppression factor up to 107. In addition, this experiment can provide new information on the cosmic-ray gamma-radiation in the energy interval 30 GeV–1 TeV, neutrons and gamma-rays from solar flares, and the existence of very massive exotic charged particles in cosmic radiation. The INCA is a calorimeter combining properties of conventional ionization calorimeters and classical neutron monitors. It can measure both the ionization produced by charged particles and evaporation neutrons arising as a result of excitation of heavy-absorber nuclei by cascade particles. The advantages of the INCA are not only excellent electron–proton separation but a high geometry factor of about 2 m 2 sr / ton owing to the INCA optimized composition and shape, whereas conventional ionization calorimeters are usually limited by geometry factor on the order of 0.1 m 2 sr / ton . To verify the INCA concept, a prototype was constructed and exposed to pion and proton accelerator beams with energies of 4 and 70 GeV, respectively, and to an electron beam with an energy of 200–550 MeV. The experimental data obtained agree well with the results of a Monte Carlo simulation by the SHIELD code.

Size dependence of frequency attenuation length of extensive air showers observed at Akeno

The size dependence of the frequency attenuation length ( Lambda ) of extensive air showers has been studied at Akeno for electron sizes between 105 and 108.5. Lambda decreases with increasing size up to 106 and increases slowly above 107. The value between 107 and 108 is 99+or-7 g cm-2. This indicates that the depth of the shower maximum above a few 1016 eV is shallower than that obtained by optical methods and is consistent with that from the equiintensity cut method. The result supports the view that heavy enriched primary particles with a conservative interaction model or proton-dominated primaries with interactions of high multiplicity are required.

Afterpulses and decay times of fast scintillation counters for extensive air shower experiments

Abstract A fast scintillation counter system to observe the arrival time distribution of relativistic particles in extensive air showers has been developed. The generation rate of afterpulses observed by a ternary plastic scintillator counter of a fast-time-response photomultiplier were studied in detail. It was found that the effect of afterpulses generated in the photomultiplier and scintillation process was negligibly small compared with that of afterpulses produced by delayed particles in the shower. It was also found that long decay components in the scintillator output can be explained as being due to afterpulses.

A large area multitube proportional counter

Abstract A large area and light weight multitube proportional counter (MTPC) has been constructed for a position detector of cosmic ray telescopes. The MTPC composed of aluminium tubes of 10 mm×10 mm cross section and 0.4 mm in thickness. The weight of an x − y pair of the MTPC is 25 kg for an effective area of 1 m×1 m and 50 kg for 1.8 m×1.8 m area, respectively. Position resolutions obtained from data of an engineering balloon experiment are better than ±0.6 cm for Z = 6 and ±0.85 cm for Z = 26.

New doors opened by the polar patrol balloon‐cosmic quark matter, micrograins and gamma rays

Balloon experiments in Antarctica make possible to observe continuously the astrophysical objects in the southern polar sky during the flight of more than 20 days. New fields and instrument for the polar balloon experiment are proposed.

Search for antimatter at the 10−7 level with the polar patrol balloon

A new annihilation technique for antimatter search is under development of the balloon experiments in the Antarctica. The capability of antiparticle‐particle discrimination of the detector is about 10−9 by combining the Cherenkov technique, 10−5, which was confirmed by using accelerator antiproton beams, and topological methods, 10−4. The polar balloon flight with the 1/4 m2 detector will reach to the flux sensitivities around 10−7 level for antiprotons and antiheliums and the 10−6 level for heavier antinuclei.