Galactic cosmic ray iron composition

We have studied the isotopic composition of galactic cosmic ray iron in the energy interval 500-750 MeV/nucleon with a visual track detector system consisting of nuclear emulsion and cellulose-nitrate plastic. Stopping iron nuclei were identified from ionization - range measurements in the two detector parts. Cone lenhths were measured in the plastic sheets and the residual ranges of the particles were measured in plastic and in emulsion. We have determined the mass of 17 iron nuclei with an uncertainty of about 0.3 amu. The isotopic composition at the detector level was found to be 52Fe:53Fe:54Fe: 55Fe:56Fe:57Fe:58Fe = 0:1:4:3:8:1:0. These numbers are not in conflict with the assumption that the isotopic composition of cosmic ray iron at the source is similar to the solar system composition.(authors)