IMP-8 observations of the spectra, composition, and variability of solar heavy ions at high energies relevant to manned space missions.
In more than 25 years of almost continuous observations, the University of Chicago's Cosmic Ray Telescope (CRT) on IMP-8 has amassed a unique database on high-energy solar heavy ions of potential relevance to manned spaceflight. In the very largest particle events, IMP-8/CRT has even observed solar Fe ions above the Galactic cosmic ray background up to approximately 800 MeV/nucleon, an energy sufficiently high to penetrate nearly 25 g/cm2 of shielding. IMP-8/CRT observations show that high-energy heavy-ion spectra are often surprisingly hard power laws, without the exponential roll-offs suggested by stochastic acceleration fits to lower energy measurements alone. Also, in many solar particle events the Fe/O ratio grows with increasing energy, contrary to the notion that ions with higher mass-to-charge ratios should be less abundant at higher energies. Previous studies of radiation hazards for manned spaceflight have often assumed heavy-ion composition and steeply-falling energy spectra inconsistent with these observations. Conclusions based on such studies should therefore be re-assessed. The significant event-to-event variability observed in the high-energy solar heavy ions also has important implications for strategies in building probabilistic models of solar particle radiation hazards.
Tylka
A J
AJ
E.O. Hulburt Center for Space Research, Naval Research Laboratory, Washington, DC 20375, USA. tylka@crs2.nrl.navy.mil
Dietrich
W F
WF
D001256:Astronomy / Q000295:instrumentation; D003359:Cosmic Radiation; D020450:Heavy Ions; D006801:Humans; D007501:Iron; D008962:Models, Theoretical; D010100:Oxygen; D011834:Radiation Monitoring / Q000295:instrumentation*; D011835:Radiation Protection; D019445:Solar Activity; D013026:Space Flight / Q000295:instrumentation*; D018531:Spacecraft / Q000295:instrumentation
D007501:Iron; D010100:Oxygen