Tamaki Kobayashi

Cosmic-Ray Spectra and Composition in the Energy Range of 10-1000 TeV per Particle Obtained by the RUNJOB Experiment

This is a full report on the cosmic-ray spectra and composition obtained by the emulsion chambers on board 10 long-duration balloons, launched from Kamchatka between 1995 and 1999. The total exposure of these campaigns amounts to 575 m2 hr, with an average flight altitude of ~32 km. We present final results on the energy spectra of two light elements, protons and helium nuclei, and on those of three heavy-element groups, CNO, NeMgSi, and Fe, covering the very high energy region of 10-1000 TeV particle-1. We additionally present the secondary/primary ratio, the all-particle spectrum, and the average mass of the primary cosmic rays. We find that our proton spectrum is in good agreement with other results, but the intensity of the helium component is nearly half that obtained by JACEE and SOKOL. The slopes of the spectra of these two elements obtained from RUNJOB data are almost parallel, with values of 2.7-2.8 in the energy range of 10-500 TeV nucleon-1. RUNJOB heavy-component spectra are in agreement with the extrapolation from those at lower energies obtained by CRN (Chicago group), monotonically decreasing with energy. We have also observed secondary components, such as the LiBeB group and the sub-Fe group, and present the secondary/primary ratio in the TeV nucleon-1 region. We determine the all-particle spectrum and the average mass of the primary cosmic rays in the energy region of 20-1000 TeV particle-1. The intensity of the RUNJOB all-particle spectrum is 40%-50% less than those obtained by JACEE and SOKOL, and the RUNJOB average mass remains almost constant up to ~1 PeV.

Successive magnetic phase transitions in Nd2CuO4

A neutron scattering study on Nd 2 CuO 4 , a mother material of the electron-doped superconductor (Nd 1- x Ce x )CuO 4- y , was carried out. Reentrant magnetic phase transitions associated with spin reorientation of antiferromagnetic ordering were observed. La 2 NiO 4 -type order was stabilized in the range 80 K\({\lesssim}T{\lesssim}\)250 K and at \(T{\lesssim}40\) K. Between 40 K\({\lesssim}T{\lesssim}\)80 K, La 2 CuO 4 -type order was realized. Diffuse scattering due to the two-dimensional spin fluctuation was also observed at around T ≃250 K.

High energy cosmic-ray electrons beyond 100 GeV

Abstract High energy cosmic-ray electrons lose their energy by synchrotron and inverse Compton processes during their propagation through the Galaxy. Then the electron spectrum brings us a unique information for the sources and propagation of cosmic-rays, and many observations have been carried out since the first discovery of cosmic-ray electrons. Beyond 100GeV, however, only a few measurements were successful to observe the absolute flux of electrons. The emulsion chamber observations were the most successful to observe the spectrum extending up to a few TeV region in collaborating with University of Washington group. Beyond 100GeV, the statistical accuracy of observed data is still limited, and we spent efforts to accumulate the data by improving the methods of detection of electrons particularly in a few hundred GeV region. We report here the results based on the new flight exposures of chambers 1996 and 1998. The statistical accuracy of electron spectrum was much improved at several hundred GeV. Our old spectrum is still consistent with the new data. The results and improvements to the observations of those high energy electrons, and their astrophysical significance are presented.

Observations of high energy primary electrons and their astrophysical significance

Abstract Cosmic-ray electrons lose their energy by synchrotron and inverse Compton processes during their propagation through the Galaxy. It has been recognized that the spectrum of electrons will bring us unique information about the propagation and acceleration of cosmic-rays. First, we review the past observations of high energy primary electrons beyond 100 GeV, and discuss the inherent technical difficulties in the direct observations of electrons in this high energy region. Next, discussion is made on the observations and their astrophysical significance to the electron spectrum in the TeV region. By these observations, it is promising to find the major contributing sources and to determine the parameters in models of propagation of cosmic-rays. Astrophysical importance is emphasized in the observations of electrons with more statistical significance in TeV region.

Superconductivities in the (Bi,Pb)-oxycarbonate system

Abstract Two (Bi,Pb)-oxycarbonate superconductors have been found by resistivity and magnetization measurements. Transition temperatures are 41 K (54K) for the low- T c phase (high- T c phase). The crystal structures were analyzed by using the HRTEM and X-ray diffraction techniques. The lattice parameters were a 0 =3.821 A , c 0 =39.444 A (a 0 =3.88 A , c 0 =54.52 A ) for low- T c phase (high- T c phase) in the tetragonal unit cell. A crystal structure model is proposed in which the chemical formula for the low- T c phase (high- T c phase) is (Bi,Pb) 2 Sr 4 Cu 2 CO 3 O 8 ((Bi,Pb) 2 Sr 6 Cu 3 (CO 3 ) 2 O 10 ), which can be described as the combination of a single (double) Sr 2 CO 3 block and a single (Bi,Pb) 2 Sr 2 O 4 block.

Superconductor with Tc up to 8 K in the compound (Ln,Ca)(Sr,Ba)2(C,Cu)Cu2O7-δ

Abstract We have synthesized a new family of oxycarbonate compounds (Ln,Ca) (Sr,Ba) 2 (C,Cu)Cu 2 O 7-δ (Ln: rare-earth metals) with a so-called “CO 3 -1212” structure. Two kinds of single phase in the general formula Er 0.5 Ca 0.5 Sr 2- x Ba x Cu 3- y C y O 7-δ with ( x , y )=(0.6, 0.5) and (1.3, 0.4) were prepared at different CO 2 partial pressures. The former compound shows a superconducting transition at about 45 K, and the latter has T c up to 80 K. This rise in T c may come from the increase of carrier density because of the decrease of carbon content. We have also studied the Ln-dependence, and it is revealed that most of the compounds Ln 0.5 Ca 0.5 Sr 0.7 Ba 1.3 Cu 2.6 C 0.4 O 7−δ show the same results, except for Ln = Ce and Tb, which did not construct the structure, and also Ln = Pr , which shows suppressed superconductivity with T c of 30 K.

Azimuthally controlled observation of heavy cosmic-ray primaries by means of the balloon-borne emulsion chamber

Abstract We have exposed an emulsion chamber with an area of 1.22 m 2 on board of the balloon at an atmospheric depth of 8.9 g/cm 2 for 15.8 h, which has been azimuthally controlled within the accuracy of Δφ = 0.5°. With the use of the east-west asymmetry effect of arriving cosmic-ray primaries, we can obtain the energy spectra for individual elements in the kinetic energy range from a few GeV/nucleon up to ∼ 15 GeV/nucleon. We present also the energy spectra obtained by the opening-angle method for the higher energy region, 5–1000 GeV/nucleon, for the elements not lighter than silicon. We find that the energy spectra obtained by the former method continue smoothly to those obtained by the latter, indicating that the energy determination using the opening-angle method is performed correctly. We compare also the present results with those obtained by the previous work. We find that the iron flux is in nice agreement with that obtained by the previous observation, the differential spectral index being constant, ∼ 2.5, up to a few TeV/nucleon, while in the case of the silicon component, it is ∼ 2.7 for 10–1000 GeV/nucleon in this work, significantly harder than the previous one, ∼ 2.9. We also report the flux of the sub-iron component and its abundance ratio to the iron component. We find the abundance ratio of [Z = 21–25]/iron is slightly less than those obtained previously in the higher energy region, ≳ 100 GeV/n.

OBSERVATIONS OF HIGH-ENERGY COSMIC-RAY ELECTRONS FROM 30 GeV TO 3 TeV WITH EMULSION CHAMBERS

We have performed a series of cosmic-ray electron observations using balloon-borne emulsion chambers since 1968. While we previously reported the results from subsets of the exposures, the final results of the total exposures up to 2001 are presented here. Our successive experiments have yielded a total exposure of 8.19 m2 sr day at altitudes of 4.0-9.4 g cm–2. The performance of the emulsion chambers was examined by accelerator beam tests and Monte Carlo simulations, and the on-board calibrations were carried out by using the flight data. In this work, we present the cosmic-ray electron spectrum in the energy range from 30 GeV to 3 TeV at the top of the atmosphere, which is well represented by a power-law function with an index of –3.28 ± 0.10. The observed data can also be interpreted in terms of diffusive propagation models. The evidence of cosmic-ray electrons up to 3 TeV suggests the existence of cosmic-ray electron sources at distances within ~1 kpc and times within ~1 × 105 yr ago.

The CALET, CALorimetric Electron Telescope, mission for the International Space Station

Abstract The CALorimetric Electron Telescope, CALET, mission is proposed for the Japanese Experiment Module Exposure Facility of the International Space Station. Major goals of the mission are precise measurements of the electrons in a few GeV - 10 TeV and the gamma-rays in 100 MeV - several TeV, keeping an energy resolution of a few % over 100 GeV. From the measurements, a systematic investigation of high-energy electromagnetic process in universe will be performed. A detection of SUSY particle which is a candidate of the dark matter would also be expected. The detector is composed of an imaging calorimeter of scintillating fibers and a total absorption calorimeter. Total thickness of the absorber is 45 r.1 for electro-magnetic particles and 2.1 m.f.p for protons. Total weight of the payload is nearly 2,200 kg, and the effective geometrical factor should be ∼ 1.0 m 2 sr. The hadron rejection power can be 10 6 for electrons.

Pressure effects on the antiferromagnetic ordering in Pr2CuO4-y

Neutron diffraction experiments have been carried out to study the effects of pressure on the antiferromagnetism in Pr 2 CuO 4- y . The intensity of magnetic scattering is sensitively affected by pressure. This result is interpreted as the changes in the spin orientations induced under high pressure. In contrast, the three-dimensional (3D) ordering temperature T N is little dependent on pressure. The absence of the pressure effect on T N indicates a marked contrast to the large effect on T N in La 2 CuO 4- y .