Since its launch the AlphaMagneticSpectrometer-02 (AMS-02) has delivered outstanding quality measurements of the spectra of cosmic-ray (CR) species, which resulted in a number of breakthroughs, including the spectrum of iron: because of the large fragmentation cross section and large ionization energy losses, most of CR iron at low energies is local, and may harbor some features associated with relatively recent supernova (SN) activity inside the Local Bubble. The analysis of new iron spectrum together with Voyager 1 and ACE-CRIS data revealed an unexpected bump in the iron spectrum and in the Fe/He, Fe/O, and Fe/Si ratios at 1–2 GV: the found excess fitted well with recent discoveries of radioactive 60Fe deposits in terrestrial and lunar samples, and in CRs. This was the first time such an excess was found in the spectrum of an element that is dominated by stable species, most notably 56Fe: it will be fundamental to measure the spectra of other heavy CR species to see if a similar spectral feature is present. Our calculations within the GALPROP–HELMOD framework provided an updated local interstellar spectrum (LIS) of iron in the energy range from 1 MeV/n to 10 TeV/n: starting from this LIS and the 60Fe/56Fe abundance measured by ACE-CRIS, Fe isotopes composition is estimated and compared to SN yields, along with the prediction of the important SubFe/Fe ratio for different scenarios.
cosmic rays; iron; heliosphere; galprop; helmod; supernovae
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