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

• DOI: 10.1126/science.aad6004
• Publication Date: 2016-04-22T03:39:02Z
• Authors: W. R. Binns; M. H. Israel; E. R. Christian; A. C. Cummings; G. A. de Nolfo; K. A. Lave; R. A. Leske; R. A. Mewaldt; E. C. Stone; T. T. von Rosenvinge; M. E. Wiedenbeck
• Keywords: Cosmic ray spallation; Radioactive decay

Iron-60 ((60)Fe) is a radioactive isotope in cosmic rays that serves as clock to infer an upper limit on the time between nucleosynthesis and acceleration. We have used ACE-CRIS instrument collect 3.55 × 10(5) iron nuclei, with energies ~195 ~500 mega-electron volts per nucleon, of which we identify 15 (60)Fe nuclei. The (60)Fe/(56)Fe source ratio (7.5 ± 2.9) 10(-5) detection supernova-produced implies required for acceleration transport Earth does not greatly exceed half-life 2.6 million years distance can diffuse over this time, ⪍1 kiloparsec. A natural place origin nearby clusters massive stars.