Measurements of the Isotopic Composition of Anomalous Cosmic Ray N, O, and Ne from ACE

We have measured the elemental and isotopic composition of anomalous cosmic rays (ACRs) with energies > 8 Me V /nucleon during solar quiet periods between August 1997 and March 1998, using the Solar Isotope Spectrometer (SIS) on the Advanced Composition Explorer (ACE). The capabilities of the SIS instrument allow the examination of spectra of individual ACR isotopes. In addition to the well-known low-energy ACR enhancements in the intensity of elemental 0 and Ne, similar enhancements are found in ^(18)O and ^(22)Ne, with relative abundances of ^(18)O/^(16)O ~ 0.002 and ^(22)Ne/(20)Ne ~ 0.1. The neon abundance ratio appears more similar to that found in the solar wind than in meteorites, and is far below that deduced for the galactic cosmic ray (GCR) source, indicating that GCRs are not simply an accelerated sample of the local interstellar medium