Makoto Hareyama

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.

A POSSIBLE APPROACH TO THREE-DIMENSIONAL COSMIC-RAY PROPAGATION IN THE GALAXY. I. STABLE NUCLEI WITHOUT ENERGY CHANGE

We extend our model of three-dimensional cosmic-ray propagation without energy change to that including energy change due to reacceleration and ionization energy loss. We assume that there is no boundary in both the radial spread of the disk and the latitudinal spread of the halo, and that the three critical parameters, the diffusion coefficient D, the gas density n, and the cosmic-ray source density Q, depend on both the space position r and the rigidity R of the cosmic-ray particle. It is possible to apply the weighted slab technique to the transport equation, even including the energy change process, if the diffusion coefficient is separable in r and R, i.e., D(; R) = (v/c)RαD(), and combining it with the first-pole approximation in the path length distribution, we can obtain the analytical solution rather easily. We show that the rigidity dependence of the secondary-to-primary ratio behaves as R-α in the high-energy region and as vRα in the low-energy region. We compare our numerical results with experimental data in both the low- and the high-energy regions and find that our model reproduces all components over the wide energy range 1 GeV nucleon-1 to 100 TeV nucleon-1, with the adoption of appropriate scale heights in D, n, and Q. We also confirm that the reacceleration process actually occurs during the propagation in the Galaxy and that its magnitude is comparable with that expected from reasonable numerical choices for three parameters, D, n, and the velocity of the hydromagnetic turbulence vM.

First Results of High Performance Ge Gamma-Ray Spectrometer Onboard Lunar Orbiter SELENE (KAGUYA)

The high precision gamma-ray spectrometer (GRS) is carried on the first Japans large-scaled lunar explorer, SELENE (KAGUYA), successfully launched by the H-IIA rocket on Sep. 14, 2007. The GRS consists of a large Ge crystal as a main detector and massive bismuth germanate crystals and a plastic scintillator as anticoincidence detectors. After a series of initial health check of the GRS, it started a regular observation on December 21, 2007. Energy spectra including many clear peaks of major elements and trace elements on the lunar surface have been measured by the GRS. Global measurement of thorium counting rate on the lunar surface is presented. The region showing the highest count rate of thorium extends from Kepler to Fra Mauro region in the Procellarum. And Apennine Bench and Aristillus region and the northwestern region of Mare Imbrium are high in thorium count rate. Second high count rate region is located in the South Pole-Aitken basin of the farside. Arago and Compton/Belkovich craters are also e...

HZE Particle and Neutron Dosages from Cosmic Rays on the Lunar Surface

The lunar surface is directly exposed to galactic cosmic rays (GCRs) and solar energetic particles (SEPs) because of the lack of atmosphere and magnetic field on the Moon. These charged particles successively interact with the lunar material and then produce secondary radiations as neutrons and gamma rays. The annual ambient dose equivalent on the lunar surface is estimated about 840 mSv/yr during the quiet period at the solar activity minimum. Particularly, GCR heavy component largely contributes by about 80% to the annual dose equivalents. The ambient dose equivalents of SEPs are also calculated for two transient solar particles events on October 28th in 2003 and January 20th 2005. The SEP protons take the largest contribution of about 90% to the dose, while the heavy components of SEPs do not contribute so much unlike GCRs. The ambient dose equivalent due to the SEP event on 2003 exceeds 2 Sv on the lunar surface. It is clear, however, that an aluminum shield with a thickness of 10 g/cm 2 effectively r...

Dynamics of solar protons in the Earth’s magnetosphere during magnetic storms in November 2004–January 2005

The processes of penetration, trapping, and acceleration of solar protons in the Earth’s magneto-sphere during magnetic storms in November 2004 and January 2005 are studied based on the energetic particle measurements on the CORONAS-F and SERVIS-1 satellites. Acceleration of protons by 1–2 orders of magnitude was observed after trapping of solar protons with an energy of 1–15 MeV during the recovery phase of the magnetic storm of November 7–8, 2004. This acceleration was accompanied by an earthward shift of the particle flux maximum for several days, during which the series of magnetic storms continued. The process of relativistic electron acceleration proceeded simultaneously and according to a similar scenario including acceleration of protons. At the end of this period, the intensification was terminated by the process of precipitation, and a new proton belt split with the formation of two maximums at L ∼ 2 and 3. In the January 2005 series of moderate storms, solar protons were trapped at L = 3.7 during the storm of January 17–18. However, during the magnetic storm of January 21, these particles fell in the zone of quasi-trapping, or precipitated into the atmosphere, or died in the magnetosheath. At the same time, the belts that were formed in November at L ∼ 2 and 3 remained unchanged. Transformations of the proton (and electron) belts during strong magnetic storms change the intensity and structure of belts for a long time. Thus, the consequences of changes during the July 2004 storm did not disappear until November disturbances.

A program for the precise observations of ultra heavy nuclei in galactic cosmic rays

The origin of galactic cosmic rays (GCRs) nuclei is still unknown. Precise observation of ultra heavy GCRs would be an important step in resolving their origin including the remaining problems in cosmic ray astrophysics. A program to observe UH nuclei in GCRs is proposed which involves the use of a high performance solid-state track detector on board a long-duration balloon. The program focuses measuring the elemental and isotopic compositions of UH nuclei up to the actinides. The observation of nuclear composition covers a wide range of scientific themes including studies of nucleosynthesis in cosmic ray sources, chemical evolution of galactic material, the characteristic time of cosmic rays, and heating and acceleration mechanisms of cosmic ray particles.

The Kaguya gamma-ray spectrometer: instrumentation and in-flight performances

A Gamma-Ray Spectrometer (GRS) had been developed as a part of the science payload for the first Japanese lunar explorer, Kaguya. The Kaguya was successfully launched from Tanegashima Space Center on September 14, 2007 and was injected into an orbit around the Moon and the mission ended on June 11, 2009. The Kaguya GRS (hereafter KGRS) has a large-volume Ge semiconductor detector of 252 cc as the main detector and bismuth-germanate and plastic scintillators as an active shielding. The Ge detector achieved an energy resolution of 3.0 keV (FWHM) for 1332 keV gamma ray in ground test despite the use of a mechanical cryocooler and observed gamma rays in energies ranging 0.2 to 12 MeV in lunar orbit. It was the first use of a Ge detector for lunar exploration. During the mission, KGRS participated in geochemical survey and investigated the elemental compositions of subsurface materials of the Moon. In this paper, we summarize the overview of the KGRS describing the design and in-flight performance of the instrument. This paper provides basic information required for reading science articles regarding the KGRSs observation data.

Germanium Gamma-Ray Spectrometer on SELENE (KAGUYA)

The Japanese lunar explorer SELENE was launched from Tanegashima Space Center on September 14, 2007. It consists of a main orbiter KAGUYA at 100 km altitude and two daughter satellites (relay satellite OKINA and VRAD satellite OUNA) with 14 scientific instruments. The high precision gamma-ray spectrometer (GRS) on KAGUYA measures 200 keV–12 MeV gamma rays to determine the elemental composition of the lunar surface. The GRS is composed of a large Ge crystal as a main detector and massive bismuth germinate (BGO) crystals and a plastic scintillator as anticoincidence detectors. The Ge detector is cooled by a Stirling cryocooler below 90 K during the observation. After successful launch of the spacecraft and initial checkouts, the GRS started the nominal observation on December 21, 2007, and the temperatures and counting rates of the GRS were confirmed to be stable. Energy spectra of gamma rays with a good energy resolution are being obtained over the lunar surface, which will allow us to make global maps of ...

Independent Component Analysis of the Gamma Ray Spectrometer data of SELENE (Kaguya)

We analyze the spectra measured by the Gamma Ray Spectrometer (GRS) on board the SELENE satellite orbiting the Moon. The spectra consist in 8192 energy channels ranging from 0 to 12 MeV and exhibiting lines of interest (O, Mg, Al, Si, Ti, Ca, Fe, K, Th, and U) superposed on a continuum. We have also analysed the data with various multivariate techniques, one of them being the Independent Component Analysis. We have used the JADE algorithm for our analysis that we focused in the energy range from 750 to 3000 keV. We identify at least three meaningful components. The first one is correlated to the Thorium map. The corresponding correlation coefficient spectrum exhibits the lines of Thorium, Potassium and Uranium. The second component is clearly correlated with the Iron as shown on its corresponding spectrum. Finally the third component seems to be related to the altitude of the spacecraft. This work shows that maps of elements such as iron will be available with the GRS data by a purely statistical analysis.

Narrow Spikes Enhanced by Electron Precipitation under the Inner Radiation Belt

The observation of energetic particles trapped in the magnetosphere has made clear that narrow spikes of these particles as observed at L∼1.6 are causally generated by the precipitation of particles trapped in the inner radiation belt. Furthermore, the occurrence frequency of these spikes is well correlated with the local time as coincident with the radio power transmitted from a VLF station located in west Australia, NWC. The results suggest that narrow spikes observed at L∼1.6 are mainly caused by the radio power from VLF transmitter, NWC located in Australia.