  How are the heavy elements formed? This has been a key open question in
physics for decades. Recent direct detections of neutron star mergers and
observations of evolved stars show signatures of chemical elements in the blue
range of their spectra that bear witness of recent nuclear processes that led
to heavy element production. The formation of heavy elements typically takes
place through neutron-capture reactions creating radioactive isotopes, which
following beta-decay turn into the stable isotopes we today can measure
indirectly in the surfaces of cool, low-mass stars or meteoritic grains. The
conditions (such as the neutron density or entropy) of these n-capture
reactions remains to date poorly constrained, and only through a
multidisciplinary effort can we, by combining and comparing observations,
experiments, and theoretical predictions, improve on one of the top 10 most
important open physics questions posed at the turn of the century. This
emphasises the need for detailed observations of the near-UV to blue wavelength
region. The shortage of spectrographs and hence spectra covering this range
with high-resolution and high signal-to-noise has for decades played a limiting
factor in our understanding of how heavy elements form in the nuclear reactions
as well as how they behave in the stellar surfaces. With CUBES we can finally
improve the observations, by covering the crucial blue range in more remote
stars and also achieve a higher signal-to-noise ratio (SNR). This is much
needed to detect and accurately deblend the absorption lines and in turn derive
more accurate and precise abundances of the heavy elements.
