Co/Ni Element Ratio in the Galactic Cosmic Rays between 0.8 and 4.3 GeV/nucleon
S.H. Sposato1, L.M. Barbier2, W.R. Binns1, E.R. Christian2, J.R. Cummings1, 
G.A. deNolfo3, P.L. Hink1, M.H. Israel1, R.A. Mewaldt3, J.W. Mitchell2, 
S.M. Schindler3, R.E. Streitmatter2, C.J. Waddington4

1 Dept of Physics & McDonnell Cntr for Space Sci, 
  Washington University, St. Louis, MO 63130, USA
2 Laboratory of High Energy Astrophysics, GSFC, Greenbelt, MD 20771, USA
3 Space Radiation Laboratory, Caltech, Pasadena, CA 91125, USA
4 Dept of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA

In a one-day balloon flight of the Trans-Iron Galactic Element Recorder (TIGER) in 1997, the instrument achieved excellent charge resolution for elements near the Fe peak, permitting a new measurement of the element ratio Co/Ni. The best fit to the data, extrapolated to the top of the atmosphere gives a result of 0.093 +/- 0.037 over the energy interval 0.8 to 4.3 GeV/nucleon; however, because a Co peak is not seen in the data, this result must be considered as an upper limit. Comparing this upper limit with calculations by Webber and Gupta (1990), suggests that at the source of these cosmic rays a substantial amount of 59Ni survived. This conclusion is in conflict with the clear evidence from ACE-CRIS below 0.5 GeV/nucleon that there is negligible 59Ni surviving at the source. Possible explanations for this apparent discrepancy will be discussed.