Letter to the Editor Evidence from Voyager and ISEE-3 spacecraft Data for the decay of secondary K-electron capture isotopes during the propagation of cosmic rays in the Galaxy

New data from the cosmic ray experiment on the Voyager spacecraft confirms and extends earlier data from a similar experiment on the ISEE-3 spacecraft which indicates the possibility of the decay of certain K-capture isotopes during the interstellar propagation of galactic cosmic rays. These cosmic ray measurements, along with the cross section measurements, indicate that ∼ 25% of the K-capture isotopes 51Cr and 49V produced as secondaries have decayed at interstellar energy of ∼ 400 MeV/nuc. This suggests a possible interstellar energy gain ∼ 100 MeV/nuc out of the current interstellar energy ∼ 500 MeV/nuc. This measurement suggests that the study of the K-capture isotopes may now have reached a level that will soon provide definitive information on the amount of reacceleration that may occur during cosmic-ray propagation after an initial acceleration in the cosmic ray sources.