Characterization Of Large-Area Silicon Ionization Detectors For The ACE Mission

We report on extensive tests of large-area (10 cm diameter) high-purity ion-implanted silicon detectors for the solar isotope spectrometer (SIS), and lithium-drifted silicon detectors for the cosmic ray isotope spectrometer (CRIS), which are under development for launch on the advanced composition explorer (ACE) mission. Depletion and breakdown characteristics versus bias were studied, as were long-term current and noise stability in a thermally cycled vacuum. Dead-layer and total thickness maps were obtained using laser interferometry, beams of energetic argon nuclei and radioactive sources of alpha particles. Results, selection criteria, and yields are presented

Two-Dimensional Position-Sensitive Silicon Detectors For The ACE Solar Isotope Spectrometer

Two-dimensional position-sensitive silicon detectors ('matrix detectors') have been designed, procured, and tested as part of the development of the solar isotope spectrometer (SIS) instrument for NASA's Advanced Composition Explorer (ACE) mission. Important characteristics of these devices include: thickness approximately 50 - 90 micrometer, active area 34 cm^2, 64 strips on each surface with 1 mm strip pitch. The SIS instrument uses four such detectors, processing signals from each of the 512 individual strips with a separate 12-bit pulse height analyzer implemented with custom-designed VLSI circuits. A set of 25 matrix detectors have been characterized through a variety of tests intended both toe select the best candidates for use in the flight instrument and to provide the calibrations needed to interpret flight data. We discuss the design of the SIS matrix detectors and present selected results from the detector tests that have been performed

Why Are Most Ground Level Events Associated with High Fe/O Ratios?

In a seminal paper about Ground Level Events (GLEs), Dietrich and Lopate (1999) reported on 24 GLEs from April, 1973 to May, 1998. They noted that alt but one of these GLEs, June 15, 1991, were associated with a Solar Energetic Particle (SEP) event with an enhanced Fe/O ratio. The Fe/O ratio observed for the June 15, 1991 event was only 0.03, well below the nominal coronal abundance of Fe/O = 0.134. For the remaining events, Fe/O ranged from 0.27 to over 3, welt over the nominal coronal value. During Solar Cycle 23, 14 more GLEs were observed, only one of which had very low Fe/O. This was the event of January 20, 2005, the largest ground-level neutron monitor event in 49 years. We will report on our efforts to find out whether the events of June 15, 1991 and January 20, 2005 have features in common, besides high Fe/O, that distinguish them from all other GLE events and may help determine the cause of elevated Fe/O in almost all GLE events. We will use energetic particle, magnetic field, and solar wind plasma data from NASA's IMP-8 Wind, and ACE spacecraft