Co/Ni element ratio in the galactic cosmic rays between 0.8 and 4.3 GeV/nucleon.

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 an upper limit for this ratio of 0.093 ± 0.037 over the energy interval 0.8 to 4.3 GeV/nucleon; because a Co peak is not seen in the data, this result is given as an upper limit. Comparing this upper limit with calculations by Webber & Gupta [14] suggests that at the source of these cosmic rays a substantial amount of the electron-capture isotope [sup 59]Ni survived. This conclusion is in conflict with the clear evidence from ACE/CRIS below 0.5 GeV/nucleon that there is negligible [sup 59]Ni surviving at the source. Possible explanations for this apparent discrepancy are discussed. [ABSTRACT FROM AUTHOR]