Lower limits on the nucleosynthezis of $^{44}$Ti and $^{60}$Fe in the dynamic spiral-arms model

TL;DR

This paper establishes lower limits on the nucleosynthesis of $^{44}$Ti and $^{60}$Fe in cosmic rays using the dynamic spiral-arms model, linking observed isotope ratios to source production and acceleration timescales.

Contribution

It introduces a method to derive lower bounds on isotope production in cosmic rays based on observed ratios and the dynamic spiral-arms model, highlighting constraints on nucleosynthesis and acceleration timescales.

Findings

Lower limit on $^{44}$Ti nucleosynthesis at the source.

Lower limit on $^{60}$Fe production based on observations.

Acceleration timescale of radioisotopes constrained to less than a century.

Abstract

We have previously focused on studying the electron-capture isotopes within the dynamic spiral-arms model and empirically derived the energy dependence of the electron attachment rate using the observation of $^{49}$Ti/$^{49}$V and $^{51}$V/$^{51}$Cr ratios in cosmic rays (Benyamin et al. 2017). We have also shown how this relation recovers the energy dependence seen in the lab measurements (Letaw et al. 1985). In this work we use this relation to construct the $^{44}$Ca/$^{44}$Ti ratio and place a lower limit on the amount of $^{44}$Ti that is required to be nucleosynthesized at the source. The results also imply that the acceleration process of the radioisotopes cannot be much longer than a century time scale (or else the required nucleosynthesized amount has to be correspondingly larger). We also provide a similar lower limit on the source $^{60}$Fe by comparing to the recently observed $^{60}$Fe/$^{56}$Fe (Binns et al. 2016).