Speaker
Prof.
Martin Israel
(Washington University in St Louis)
Description
The Cosmic Ray Isotope Spectrometer (CRIS) on the ACE spacecraft has been measuring the isotopic composition of Galactic Cosmic Rays (GCRs) since October 1997. Using selected data from the past seventeen years, we have a set of 3.55 x 10^5 Fe nuclei in the energy interval ~240 to ~470 MeV/nucleon with excellent mass resolution characterized by sigma = 0.24 amu. In this data set we have detected fifteen well resolved iron-60 nuclei. Iron-60 is beta- unstable with a half-life 2.6 million years. The detection of these radioactive nuclei permits us to set an upper limit of a few million years on the time between nucleosynthesis of these nuclei and their acceleration to cosmic-ray energy. A lower limit of ~10^5 years was established by the CRIS observation that the electron-capture isotope nickel-59 is essentially absent in the GCRs. These two limits bracket the nucleosynthesis-to-acceleration time to a range that is consistent with the emerging evidence that the bulk of GCRs are accelerated in associations of massive stars (OB associations).
| Registration number following "ICRC2015-I/" | 68 |
|---|---|
| Collaboration | -- not specified -- |
Author
Prof.
Martin Israel
(Washington University in St Louis)
Co-authors
Dr
Alan Cummings
(California Institute of Technology)
Prof.
Edward Stone
(California Institute of Technology)
Dr
Eric Christian
(NASA/GSFC)
Dr
Georgia de Nolfo
(NASA/GSFC)
Dr
Kelly Lave
(Washington University in St. Louis)
Dr
Mark Wiedenbeck
(Jet Propulsion Laboratory)
Dr
Richard Leske
(California Institute of Technology)
Dr
Richard Mewaldt
(California Institute of Technology)
Dr
Tycho von Rosenvinge
(NASA/GSFC)
Prof.
Walter Binns
(Washington University in St. Louis)
