Event‐integrated fluxes of protons and alpha particles in solar‐flare‐associated particle events during solar cycle 21 (1976–1986) are determined from data obtained by detectors on board the IMP‐7 and IMP‐8 satellites. Sixty‐three solar particle events with proton fluence (E > 10 MeV) > 107 cm−2 were identified from October 1972 to March 1987. The average omnidirectional flux of protons with kinetic energy > 10 MeV for cycle 21, 64 cm−2s−1, is lower than the corresponding number for cycle 20 (92 cm−2s−1) based on satellite data and for the cycle 19 (378 cm−2s−1) based on lunar sample data. Six large events contributed 70% of the total proton fluence during solar cycle 21. Several events in early 1981 with high proton fluences could account for much of the high 56Co radioactivities observed in the small‐sized Salem meteorite. The event‐averaged alpha‐particle to proton ratio in the energy interval 1–10 MeV/nucleon varies from 0.006 to 0.05, with an average value of 0.02 for the whole cycle. The events during solar cycle 21 are characterized by softer spectra for both protons and alpha particles compared to those in earlier solar cycles. No definitive correlation exists between cycle‐averaged solar flare proton fluxes and peak sunspot numbers. A comparison with long‐term (million year) averaged data for these parameters, obtained from lunar sample data, shows that the contemporary solar flare proton spectra are characterized by softer spectra (lower R0 values). A similar comparison cannot be made for the mean long‐term averaged flux, as the contemporary average suffers from uncertainty due to statistics of single events. For this reason, the solar energetic particle activity for the last two solar cycles cannot be considered as representative of average solar particle activity over longer time periods.
Historically, proton-induced single-event effects (SEEs) ground test data are collected independent of the orientation of the microelectronic device to the proton beam direction. In this study, we present experimental and simulation evidence that shows an effect of over an order of magnitude on the proton-induced single-event upset (SEU) cross section when the angle of incidence of the proton beam is varied. The magnitude of this effect is shown to depend on the incidence proton energy and the device critical charge. The angular effect is demonstrated for Silicon-On-Sapphire and Silicon-On-Insulator technologies, but would not necessarily be limited to these technologies.
Abstract-The near-Earth asteroid rendezvous (NEAR)-Shoemaker remote-sensing x-ray/gammaray spectrometer (XGRS) completed more than a year of operation in orbit and on the surface of 433 Eros. Elemental compositions for a number of regions on the surface of Eros have been derived from analyses of the characteristic x-ray and gamma-ray emission spectra. The NEAR XGRS detection system was included as part of the interplanetary network (IPN) for the detection and localization of gamma-ray bursts (GRBs). Preliminary results for both the elemental composition of the surface of Eros and the detection of GRBs have been obtained. In addition to the science results, the design and operation of the NEAR XGRS is considered. Significant information important for the design of future remote sensing XGRS systems has been obtained and evaluated. We focus on four factors that became particularly critical during NEAR: (1) overall spacecraft design, (2) selection of materials, (3) increase of the signal-to-noise ratio and (4) knowledge of the incident solar x-ray spectrum.
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