Galactic Chemical Evolution of Radioactive Isotopes
  The presence of short-lived ($\sim$\,Myr) radioactive isotopes in meteoritic
inclusions at the time of their formation represents a unique opportunity to
study the circumstances that led to the formation of the Solar System. To
interpret these observations we need to calculate the evolution of
radioactive-to-stable isotopic ratios in the Galaxy. We present an extension of
the open-source galactic chemical evolution codes NuPyCEE and JINAPyCEE that
enables to track the decay of radioactive isotopes in the interstellar medium.
We show how the evolution of isotopic ratio depends on the star formation
history and efficiency, star-to-gas mass ratio, and galactic outflows. Given
the uncertainties in the observations used to calibrate our model, our
predictions for isotopic ratios at the time of formation of the Sun are
uncertain by a factor of 3.6. At that time, to recover the actual
radioactive-to-stable isotopic ratios predicted by our model, one can multiply
the steady-state solution (see Equation~1) by $2.3^{+3.4}_{-0.7}$. However, in
the cases where the radioactive isotope has a half-life longer than
$\sim$\,200\,Myr, or the target radioactive or stable isotopes have mass-
and/or metallicity-depended production rates, or they originate from different
sources with different delay-time distributions, or the reference isotope is
radioactive, our codes should be used for more accurate solutions. Our
preliminary calculations confirm the dichotomy between radioactive nuclei in
the early Solar System with $r$- and $s$-process origin, and that $^{55}$Mn and
$^{60}$Fe can be explained by galactic chemical evolution, while $^{26}$Al
cannot.
