SOURCE ABUNDANCES OF ULTRA HEAVY-ELEMENTS DERIVED FROM UHCRE MEASUREMENTS

A total of 205 tracks have been located, measured, and positively iden titied as originating from Ultra Heavy (Z greater than or equal to 65) cosmic ray ions with energies over 2 GeV/amu in the 10 UHCRE plastic track detector (mainly Lexan polycarbonate) stacks studied by our Grou p. About 40 values of reduced etch rate S have been obtained along eac h of these tracks. A method based on determining the gradient of S, to gether with calibration in accelerators, is used to determine the char ge of each ion resulting in one of such tracks to obtain the charge sp ectrum of the recorded Ultra Heavy ions. The abundance ratio of ions w ith 87 less than or equal to Z less than or equal to 100, to those wit h 74 less than or equal to Z less than or equal to 86, as well as that of ions with 81 less than or equal to Z less than or equal to 86 to t hose with 74 less than or equal to Z less than or equal to 80 are calc ulated at 0.016 and 0.32, respectively, which agree with the values ob tained from measurements in the HEAO-3 and Ariel-6 experiments. The ab undance ratio of ions with 70 less than or equal to Z less than or equ al to 73 to those with 74 less than or equal to Z less than or equal t o 86 is also calculated, but its value (0.074) did not seem to be sign ificant because of our detectors' low registration efficiency in the c harge range 70 less than or equal to Z less than or equal to 73. A com puter program developed by our Group, based on the Leaky Box cosmic ra y propagation model, has been used to determine the source abundances of cosmic ray nuclei with Z greater than or equal to 65 inferred from the abundances measured in the UHCRE. It appeared that r-process synth esized elements were overabundant compared to the Solar System abundan ces, as predicted by other authors. Copyright (C) 1996 Elsevier Scienc e Ltd