The cosmic ray actinide charge spectrum derived from a 10 m(2) array of solid state nuclear track detectors in Earth orbit

The DIAS-ESTEC Ultra Heavy Cosmic Ray Experiment (UHCRE) on the Long Durati on Exposure Facility, collected approximately 3000 cosmic ray nuclei with Z > 65 in the energy region E > 1.5 GeV nucleon(-1) during a six year exposu re in Earth orbit. The entire accessible collecting area of the solid state nuclear track detector (SSNTD) array has been scanned for actinides, yield ing a sample of 30 from an exposure of approximate to 150 m(2) sr yr. The U HCRE experimental setup is described and the observed charge spectrum prese nted. The current best value for the cosmic ray actinide relative abundance , (Z > 88)/(74 less than or equal to Z less than or equal to 87), is report ed. (C) 2001 Elsevier Science Ltd. All rights reserved.