Induced activation study of LDEF

Abstract

Analysis of the induced radioactivity of LDEF is continuing with extraction of specific activities for various spacecraft materials. Data and results of activation measurements from eight national facilities are being collected for interpretation. The major activation mechanisms in LDEF components is the proton flux in the South Atlantic Anomaly (SAA) inner radiation belt. This flux is highly anisotropic, and exposes the west side of the spacecraft to higher radiation doses. The directionally dependent activation due to these protons has clearly been observed in the data from Al experiment tray clamps, steel trunnions, and is also indicated by the presence of a variety of radioisotopes in other materials. A secondary production mechanism, thermal neutron capture, was observed in two materials having large capture cross sections, Co and Ta. The neutrons could be thermalized in nearby low Z material, although this has yet to be verified. Specific activities are presented for a number of materials which show SAA effects and thermal neutron capture. Trends are examined in the measured results that show the effect of shielding and non-SAA related activation.