CHARGE-STATE OF ANOMALOUS COSMIC-RAY NITROGEN, OXYGEN, AND NEON - SAMPEX OBSERVATIONS

We report observations of the ionization state of anomalous cosmic-ray (ACR) nitrogen, oxygen, and neon during the period 1992 October to 19 93 May, carried out with instrumentation on the SAMPEX spacecraft. The low-altitude (510 x 675 km) and high-inclination (82-degrees) orbit e nables SAMPEX to sample the interplanetary ACR fluxes on each polar pa ss and then to observe the cutoff of these fluxes by the geomagnetic f ield at lower latitudes. The arrival time and direction of each ion is recorded by the instruments, allowing detailed calculations of the pa rticle's trajectory through the Earth's magnetic field and thereby pla cing upper limits on the ionization state of the particles. We find (a ) that ACR nitrogen, oxygen, and neon each contain singly ionized part icles and (b) that ACR oxygen is predominantly singly ionized with an upper limit of 10% for higher ionization states. These ionization stat es confirm theories of ACR origin as neutral interstellar material tha t is singly ionized near the Sun by UV or charge exchange with the sol ar wind, and is subsequently accelerated in the outer heliosphere.