T. Yanagimachi

New two-dimensional position sensitive silicon detector with good position linearity and resolution

Abstract A two-dimensional position sensitive silicon detector (PSSD) with a good linear response, consisting of a square ion-implanted resistive anode with a boundary of an additional resistive-strip electrode, was newly developed. Linearity and resolution for the PSSD were investigated using 40 MeV helium and 95 MeV nitrogen ion beams. The PSSD has an effective area of 45 mm×45 mm, a thickness of 400 μm, a junction capacitance of 500 pF, a surface resistance of the ion-implanted resistive anode of 18 kω□ and a resistance of the strip line of 1.4 kω. The nonlinearities and resolutions (FWHM) of the position were 0.75% and 1.97 mm for 40 MeV helium ions obtained by 6 μs pulse shaping, and 0.47% and 0.71 mm for 95 MeV nitrogen ions obtained by 12 μs pulse shaping, respectively.

Improvement of mass resolution of cosmic ray nuclei using a ΔE × E Si detector telescope

Using 5-in.-diameter Si(Li) detectors with a detector thickness of 1, 2 and 3 mm combined with 62 mm × 62 mm position-sensitive Si detectors, an excellent isotope telescope has been constructed for the Geotail mission. The performance of the telescope and the individual detectors has been investigated using 56Fe beams with energies between 430 and 696 MeV/n. The nonuniformity of the detector thickness as measured by exposing the detectors to a monochromatic Fe beam is 0.44% for 1 mm thick detectors, 0.54% for 2 mm thick detectors and 0.15% for 3 mm thick detectors. The secondary isotopes of Al through Fe produced by 430 MeV/n 56Fe in a polyethylene target were clearly resolved by the telescope. The measured mass resolution for Si, Ca and Mn were 0.36 amu, 0.42 amu and 0.44 amu in FWHM, respectively. The telescope has the following two key features: an excellent resolution (better than 0.5 amu) and an exceptionally high sensitivity (SΩ = 43 cm2sr) for a broad range of species from He through Ni with energies between 2.4 and 210 MeV/n.

CHARGE WAVEFORM OF A NEW TWO-DIMENSIONAL POSITION-SENSITIVE SILICON DETECTOR.

The operation principles of the two-dimensional position-sensitive silicon detector newly developed by Doke et al. were studied using a simple model. This model treats the detector as an area of continuously distributed capacitance C and resistance Rs of position surface layer. A linear relationship can then be obtained between the position of the incident particle and change collected at the contacts of the detector. The kinetics of charge collected at corner contacts, ballistic deficit and noise were calculated. Rise time of the charge pulse (10–90%) was found to vary with the position of incidence up to about RsC/8. It was found that a shaping time constant longer than RsC/3 is required for pulse shaping with single CR-differentiation and single CR-integration in order to obtain a ballistic deficit of less than 1%.

The first observation of sulfur in anomalous cosmic rays by the Geotail and the wind spacecrafts

The Geotail high-energy particle instruments have observed cosmic-ray particles in the energy range from 3 MeV n-1 to 150 MeV n-1 at 1 AU during the period 1992 September-1995 August. A remarkable enhancement of anomalous cosmic-ray (ACR) N, O, Ne, and C is observed during the period. A measurable enhancement of the sulfur flux below about 20 MeV n-1 was observed. This is the first evidence showing the existence of sulfur in the anomalous component. The flux increase of anomalous sulfur, with a first ionization potential (FIP) of 10.4 eV, is smaller than that of ACR carbon with an FIP of 11.3 eV and much smaller than those of high-FIP elements, which suggests that the fractions of neutral carbon and sulfur atoms are significantly low in the very local interstellar medium.

Rapid recovery of anomalous cosmic ray flux at 1 Au in solar cycle 22

A new observation of low energy cosmic ray particles with the energies from 4 to 120 MeV/n by the HEP instrument onboard the GEOTAIL satellite orbiting at 1 AU shows a remarkable enhancement of anomalous cosmic ray (ACR) N, O and Ne in the period September 1992–December 1993 before approaching to the solar minimum in solar cycle 22. The ACR fluxes obtained by the GEOTAIL observation are in good agreement with the results earlier obtained from the SAMPEX satellite [Mewaldt et al. 1993a,b]. The ACR carbon is also evident though the C enhancement is small compared with those of N, O and Ne. We confirm the new SAMPEX finding that the ACR fluxes have recovered more rapidly in 1992–1993 than in previous solar cycles and find this tendency continues to the end of 1993.

Composition and energy spectra of anomalous cosmic rays observed by the GEOTAIL satellite

Abstract The composition and energy spectra of anomalous cosmic-rays (ACRs) in the energies 6 – 200 MeV/n have been measured during the period from September 1992 to August 1995 using the High Energy Particle instrument onboard the GEOTAIL satellite orbiting at 1 AU. A remarkable enhancement of ACR N, O, Ne and Ar is observed during the period. A flux enhancement of anomalous argon at 1 AU is confirmed by the GEOTAIL satellite. The first possible evidence for the emergence of a measurable sulfur component in ACR below about 20 MeV/n is found. The flux increase of anomalous sulfur with 10.4 eV FIP is smaller than that of ACR carbon with 11.3 eV FIP, and much smaller than those of high FIP elements, which suggests that the fraction of neutral carbon and sulfur atoms is significantly lower in the very local interstellar medium.

The wide band spectrometer for the solar flare satellite SOLAR-A

Abstract The Wide Band Spectrometer (WBS) for the solar flare satellite SOLAR-A scheduled for launch in 1991 consists of three kinds of detectors to observe the wide band spectrum from soft X-rays to gamma-rays. The soft X-ray spectrometer (gas proportional counter), hard X-ray spectrometer (NaI scintillation counter and gamma-ray spectrometer (two BGO scintillation counters) cover the 2–30 keV, 20–400 keV and 0.2–100 MeV bands, respectively. Further, the WBS contains a radiation belt monitor consisting of a NaI scintillation counter which is capable of detecting cosmic gamma-ray bursts. The details of these detectors, electronics systems and data collection are described.

The correlation between cir ion intensity and solar wind speed at 1 AU

Abstract We have investigated the relationship between solar wind speeds and the energetic proton intensity associated with corotating interaction regions (CIR) observed at 1 AU during 1973 – 1995 using NSSDC Data. The speed-difference between the high-speed solar wind and the slow-speed solar wind, which forms CIR at outer heliosphere, shows a good correlation with the peak intensity of 1 – 2 MeV protons during the solar quiet periods. The speed-difference is probably related to the shock strength of the reverse shock of the CIR formed beyond ∼ 1 AU. We have also found the solar activity dependence of the correlation between these quantities in CIR events during the period between 1973 and 1995. The intensity of CIR particles during the solar active periods is higher than that during the quiet periods, suggesting that the density of seed particles in CIR events during the solar active periods is larger than that during the solar quiet period.

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.

Observation of galactic cosmic ray particles by the HEP-HI telescope on the GEOTAIL satellite

Abstract The energy spectra (40 to 300 MeV/n) of galactic cosmic ray particles (C, N, O, Ne, Mg, Si, and Fe) observed by the HEP-HI silicon detector telescope onboard the GEOTAIL satellite were investigated over the period from January 1993 to May 1996, from the viewpoint of solar modulation. From the GEOTAIL data and those of relativistic heavy particles observed by HEAO-3, the modulation potential φ was obtained by using a solution of the Fokker-Plank equation with the “force-field” approximation. In the equation the diffusion coefficient was used as adjustable parameter, under the assumptions of a fixed velocity of solar wind (400km/sec) and the radius of the heliosphere of 50AU. The time variation of the modulation potential thus obtained is compared with that obtained from the CLIMAX neutron monitor. A reasonable correlation between both time variations is found when five months delay is applied to the results obtained by the HEP-HI telescope.