Neutron-capture elements record the ordered chemical evolution of the
  disc over time
  An ensemble of chemical abundances probing different nucleosynthetic channels
can be leveraged to build a comprehensive understanding of the chemical and
structural evolution of the Galaxy. Using GALAH DR3 data, we seek to trace the
enrichment by the supernovae Ia, supernovae II, asymptotic giant branch stars,
and neutron-star mergers and/or collapsars nucleosynthetic sources by studying
the [Fe/H], [$\alpha$/Fe], [Ba/Fe], and [Eu/Fe] chemical compositions of
$\sim$50,000 red giant stars, respectively. Employing small
[Fe/H]-[$\alpha$/Fe] cells, which serve as an effective reference-frame of
supernovae contributions, we characterise the abundance-age profiles for
[Ba/Fe] and [Eu/Fe]. Our results disclose that these age-abundance relations
vary across the [Fe/H]-[$\alpha$/Fe] plane. Within cells, we find negative
age-[Ba/Fe] relations and flat age-[Eu/Fe] relations. Across cells, we see the
slope of the age-[Ba/Fe] relations evolve smoothly and the [Eu/Fe] relations
vary in amplitude. We subsequently model our empirical findings in a
theoretical setting using the flexible Chempy Galactic chemical evolution (GCE)
code, using the mean [Fe/H], [Mg/Fe], [Ba/Fe], and age values for stellar
populations binned in [Fe/H], [Mg/Fe], and age space. We find that within a
one-zone framework, an ensemble of GCE model parameters vary to explain the
data. Using present day orbits from \textit{Gaia} EDR3 measurements we infer
that the GCE model parameters, which set the observed chemical abundance
distributions, vary systematically across mean orbital radii. Under our
modelling assumptions, the observed chemical abundances are consistent with a
small gradient in the high mass end of the initial mass function (IMF) across
the disc, where the IMF is more top heavy towards the inner disc and more
bottom heavy in the outer disc.
