N. Hasebe

Gamma-ray spectrometer for Japanese lunar polar orbiter

Abstract We review the current status of the development of Gamma-Ray Spectrometer (GRS) for the Lunar mission SELENE. The GRS instrument will measure gamma-rays in the energy range from 100 keV to 9 MeV. The instrument is a high-purity Ge detector surrounded by BGO and plastic scintillators which are operated as an anticoincidence shield, and is cooled by a Stirling cycle cryocooler. The primary objective is to provide global maps of the lunar composition. Measurements are anticipated for Fe, Ti, U, Th, K, Si, Mg, Al, O, Ca and Na over the entire lunar surface. The abundance of water ice in the permanently shaded craters at both the lunar poles will be measured with this instrument.

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.

Energy loss of relativistic electrons and its fluctuation in gas proportional counters

Abstract Absolute measurements of the energy loss and its fluctuation of relativistic electrons in this gas layer over the momentum region of 50–800 MeV/ c have been extensively achieved with high accuracy using a 100 cm proportional counter, operated with a conventional mode or a special mode (the central wire is divided by a small glass bead into two sensitive lengths of 10 cm and 90 cm). The counter is filled with Ar + 10% CH 4 mixture at various pressures between 0.1 and 2.0 atm. The experimental distributions of the energy losses are compared with those predicted by the Landau theory, the Blunck-Leisegang theory, the Chechin-Ermilova theory and the Monte Carlo method (Ispiryan et al., Cobb et al. and Ermilova et al.). The observed fractional widths agree relatively well with those of the Monte Carlo calculations. The observed values of the most probable energy losses for small thickness (≤3 × 10 −2 g/cm 2 ) of gas layer are 10–25% smaller than those predicted by the Landau-Sternheimer theory and they approach to the theoretical ones with increase of the thickness. A part of such a discrepancy between the theory and the experiment may be explained by the fact that the inner shell electrons of argon atoms in the absorber material do not contribute to the most probable energy loss, when the energy loss is not larger than the binding energy of K-shell electrons. The explanation, however, does not give an understanding for the fact that even when the thickness of gas layer is equal for the short and long counters, the difference in the most probable value between both counters is larger than that predicted by the Landau-Sternheimer theory. This suggests that the density effect correction given by Sternheimer may be insufficient to the thin gas layer. The observed most probable values are also compared with those predicted by the Chechin-Ermilova theory and the Monte Carlo method (Cobb et al. and Ermilova et al.). These predictions do not give a satisfactory explanation for the decrease of the observed values. However, the Monte Carlo results calculated by Ermilova et al. show the tendency close to the observed data.

The CALorimetric Electron Telescope (CALET) for high-energy astroparticle physics on the International Space Station

The CALorimetric Electron Telescope (CALET) is a space experiment, currently under development by Japan in collaboration with Italy and the United States, which will measure the flux of cosmic-ray electrons (and positrons) up to 20 TeV energy, of gamma rays up to 10 TeV, of nuclei with Z from 1 to 40 up to 1 PeV energy, and will detect gamma-ray bursts in the 7 keV to 20 MeV energy range during a 5 year mission. These measurements are essential to investigate possible nearby astrophysical sources of high energy electrons, study the details of galactic particle propagation and search for dark matter signatures. The main detector of CALET, the Calorimeter, consists of a module to identify the particle charge, followed by a thin imaging calorimeter (3 radiation lengths) with tungsten plates interleaving scintillating fibre planes, and a thick energy measuring calorimeter (27 radiation lengths) composed of lead tungstate logs. The Calorimeter has the depth, imaging capabilities and energy resolution necessary for excellent separation between hadrons, electrons and gamma rays. The instrument is currently being prepared for launch (expected in 2015) to the International Space Station ISS, for installation on the Japanese Experiment Module - Exposure Facility (JEM-EF).

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.

Acceleration and losses of energetic protons and electrons during magnetic storm on August 30-31, 2004

Variations of particle fluxes during a moderate magnetic storm on August 30–31, 2004 are analyzed in this paper using measurements on low-orbit polar satellites CORONAS-F and SERVIS-1. The Earth’s radiation belts were filled at this time by enhanced flux of energetic particles accelerated a month ago during magnetic storms on July 23–27. The analysis has shown that even during a moderate magnetic storm a set of several adiabatic and non-adiabatic processes is observed, which leads to acceleration or release of particles and acts selectively depending on the energy range and charge of particles.

Scintillating fiber camera for neutron dosimetry in spacecraft

Abstract A scintillating fiber camera for three-dimensional imaging was newly developed for radiation dosimetry in spacecraft. The camera consists of a scintillating fiber stack, an image intensifier unit and photomultipliers for triggering events. The scintillating fiber stack has 100 scintillating fiber layers. The layers are alternatively stacked up to be perpendicular to each other. The stack is coupled to a two-stage image intensifier and then coupled to a CCD camera for the track readout. Each fiber layer consists of 100 scintillating fibers and the fiber stack composed of 100 layers leads us to a sensitive volume of 50×50×50 mm 3 . Each fiber has a cross-section of 0.5×0.5 mm 2 . It is found that the camera has the capability to clearly identify charged particles, neutrons and γ-rays by observing individual three-dimensional images of those tracks. The threshold energy for identification of neutrons and γ-rays is 5– 10 MeV for recoil proton energy when the coincidence signals from 2 photomultipliers are used as triggers and is expected to be 2–3 MeV when the triggers from either photomultiplier are used. The whole energy region for neutron dosimetry will be covered by the combination with the Bonner spheres for the energy region lower than ∼10 MeV .

Response of piezoelectric lead zirconate titanate detector to oblique impact with hypervelocity iron particles

A cosmic dust detector using piezoelectric lead zirconate titanate (PZT) is currently being developed for use onboard a spacecraft for the BepiColombo mission. The characteristics of the PZT detector were studied by carrying out hypervelocity impact measurements with iron particles supplied by a Van de Graaff accelerator. The measurements with particle velocities of less than 5 km/s showed a linear relationship between the output voltages obtained from the detector and the particle momenta. This linear relationship obtained was almost independent of the impact angle between the particle and the PZT surface.

Electron and ion spectrometer onboard the Nozomi spacecraft and its initial results in interplanetary space

Abstract The electron and ion spectrometer (EIS) is one of the fourteen instruments onboard the Nozomi spacecraft, a Mars orbiter, launched on July 4, 1998. EIS consists of two kinds of telescopes (TOF– E and ΔE – E telescopes) designed to measure the fluxes of electrons and ions in the energy range from ∼40 keV to a few MeV. The ΔE – E telescopes are used to measure electrons and protons, while the TOF– E telescope is mainly used to measure He, CNO-group, NeMgSi-group, and Fe-group. In this paper, (a) the objectives of this experiment, (b) the details of the instrument and (c) initial results of the observation in interplanetary space are described.

Search for GeV Gamma-ray Counterparts of Gravitational Wave Events by CALET

We present results on searches for gamma-ray counterparts of the LIGO/Virgo gravitational-wave events using CALorimetric Electron Telescope ({\sl CALET}) observations. The main instrument of {\sl CALET}, CALorimeter (CAL), observes gamma-rays from