We have previously focused on studying the electron-capture isotopes within the dynamic spiral-arms cosmic-rays propagation model and empirically derived the energy dependence of the electron attachment rate using the observation of 49Ti/49V and 51V/51Cr ratios in cosmic rays. We have also shown how this relation recovers the energy dependence seen in the lab measurements. In this work, we use this relation to construct the 44Ti/44Ca ratio and place a lower limit on the amount of 44Ti that is required for it to be nucleosynthesized at the source. The results also imply that the acceleration process of the radioisotopes cannot be much longer than a century timescale (or else the required nucleosynthesized amount has to be correspondingly larger). We also provide a similar lower limit on the source 60Fe by comparing to the recently observed 60Fe/56Fe.
Bibliographical noteFunding Information:
The authors wish to thank Michael Paul for use valuable suggestions. N.J.S. gratefully acknowledges the support of the Israel Science Foundation (grant No. 1423/15) and the I-CORE Program of the Planning and Budgeting Committee and the Israel Science Foundation (center 1829/12).
© 2018. The American Astronomical Society. All rights reserved.
- Galaxy: kinematics and dynamics
- cosmic rays