Constraints on the time delay between nucleosynthesis and cosmic-ray acceleration from observations of Ni-59 and Co-59

Measurements of the abundances of cosmic-ray Ni-59 and Co-59 are reported f rom the Cosmic-Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer. These nuclides form a parent-daughter pair in a radioactive decay which can occur only by electron capture. This decay cannot occur once the nuclei are accelerated to high energies and stripped of their electrons. T he CRTS data indicate that the decay of Ni-59 to Co-59 has occurred, leadin g to the conclusion that a time longer than the 7.6 x 10(4) yr half-life of Ni-59 elapsed before the particles were accelerated. Such long delays indi cate the acceleration of old, stellar or interstellar material rather than fresh supernova ejecta. For cosmic-ray source material to have the composit ion of supernova ejecta would require that these ejecta not undergo signifi cant mixing with normal interstellar gas before similar to 10(5) yr has ela psed.