Constraints on the Time Delay between Nucleosynthesis and Cosmic-Ray Acceleration from Observations of [TSUP]59[/TSUP]N[CLC]i[/CLC] and [TSUP]59[/TSUP]C[CLC]o[/CLC]

Abstract

Measurements of the abundances of cosmic-ray 59 Ni and 59 Co are reported from 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. The CRIS data indicate that the decay of 59 Ni to 59 Co has occurred, leading to the conclusion that a time longer than the yr half-life of 59 Ni elapsed before the particles 4 7.6 # 10 were accelerated. Such long delays indicate the acceleration of old, stellar or interstellar material rather than fresh supernova ejecta. For cosmic-ray source material to have the composition of supernova ejecta would require that these ejecta not undergo significant mixing with normal interstellar gas before ∼10 5 yr has elapsed.

Observation of the 60 Fe nucleosynthesis-clock isotope in galactic cosmic rays

“…With the same method, using charge-changing instead of mass-changing crosssections, we have also estimated the 60 Fe/Fe ratio at the cosmic-ray acceleration source, using λ Fe = 2.94 g/cm 2 , and find it to be Q 60 /Q Fe = (6.2 ± 2.4) × 10 -5 . We note that the uncertainty in the 56 Fe abundance is much smaller than the statistical uncertainty of 60 Fe and does not significantly contribute to that of the 60 Fe/ 56 Fe ratio.…”

The Nine Lives of Cosmic Rays in Galaxies

“…The high 22 Ne/ 20 Ne ratio together with the lack of the unstable 59 Ni in CRs (Wiedenbeck et al 1999) yield important time constraints for CR acceleration in massive-star clusters: it should take place soon (< few Myr) after enrichment of the ambient medium in 22 Ne by the Wolf-Rayet winds, and about 0.1 Myr after a supernova explosion to avoid accelerating freshly synthesized 59 Ni. This may be possible if the injections of 22 Ne-rich wind material and of 59 Ni-rich supernova ejecta are sufficiently separated in time (Binns et al 2007) and if 59 Ni largely remains inside the supernova ejecta, beyond reach of the forward shock wave (Prantzos 2012).…”

Effect of Supernovae on the Local Interstellar Material

“…Once it is accelerated to high energy, the 59 Ni is stripped off electrons, and therefore cannot decay. Data from the CRIS experiment show a lack of 59 Ni in GCRs, indicating that the 59 Ni has decayed from the amount one would expect from a SN explosion [192]. Therefore Wiedenbeck et al (1999, [192]) suggest that acceleration of the material took place at least 76,000 years after it was ejected.…”