The Isotopic Composition of Anomalous and Galactic Cosmic Rays from SAMPEX

Abstract

New measurements of the anomalous cosmic ray (ACR) isotopic composition are presented, using data from the Mass Spectrometer Telescope (MAST) on SAMPEX. At high invariant latitudes or in interplanetary space, ACR isotopic composition measurements require correction for contamination from galactic cosmic rays (GCRs); however, at lower latitudes singly-charged ACRs can penetrate the Earth's magnetic field while fully stripped GCRs of similar energies are excluded, allowing us to study a pure ACR sample. Preliminary values for ACRs obtained using this geomagnetic filter approach are: ^(15)N /N < 0.032, ^(18)0/^(16)0 < 0.0057, and ^(22)Ne = ^(20)Ne = 0.087(+0.137, -0.026). We compare our values with those found by previous investigators and with those measured in other samples of solar and galactic material.