The Isotopic Composition of Anomalous Cosmic Ray Neon

We have used observations of neon in the energy interval 14.6 - 35.6 MeV /nuc from the cosmic-ray experiment on the Voyager 2 (V2) spacecraft during 1986-1988 to derive the ^(22)Ne/^(20)Ne ratio for the source material of the anomalous cosmic rays (ACRs). Because of the relatively small contamination from galactic cosmic-ray (CCR) neon during the time period selected, we have significantly improved the precision with which this ratio is known. We find that the derived ACR source ratio, ^(22)Ne/^(20)Ne = 0.077 +0.068/-0.043, is consistent with the composition of the solar wind (0.073) and meteoritic neon-A (0.12), but inconsistent with the galactic cosmic ray source (0.43). This finding places new limits on the possible source material of the anomalous component. If the anomalous component does derive from the inward flowing interstellar neutral gas, then the composition of the source of galactic cosmic rays differs from that of the very local interstellar medium (VLISM)