The Isotopic Composition of Anomalous Cosmic Rays from SAMPEX

Measurements of the anomalous cosmic ray (ACR) isotopic composition have been made in three regions of the magnetosphere accessible from the polar Earth orbit of SAMPEX, including the interplanetary medium at high latitudes and geomagnetically trapped ACRs. At those latitudes where ACRs can penetrate the Earth's magnetic field while fully stripped galactic cosmic rays (GCRs) of similar energies are excluded, a pure ACR sample is observed to have the following composition: ^(15)N/N < 0.023, ^(18)O/^(16)O < 0.0034, and ^(22)Ne/^(20)Ne = 0.077(+0.085, -0.023). We compare our values with those found by previous investigators and with those measured in other samples of solar and galactic material. In particular, a comparison of ^(22)Ne/^(20)Ne measurements from various sources implies that GCRs are not simply an accelerated sample of the local interstellar medium