  Thorium ions exhibit unique nuclear properties with high relevance for
testing symmetries of nature, and Paul traps feature an ideal experimental
platform for performing high precision quantum logic spectroscopy. Loading of
stable or long-lived isotopes is well-established and relies on ionization from
an atomic beam. A different approach allows trapping short-lived isotopes
available as alpha-decay daughters, which recoil from a thin sample of the
precursor nuclide. A prominent example is the short-lived $^{229\text{m}}$Th,
populated in a decay of long-lived $^{233}$U. Here, ions are provided by an
external source and are decelerated to be available for trapping. Such setups
offer the option to trap various isotopes and charge states of thorium.
Investigating this complex procedure, we demonstrate the observation of single
$^{232}$Th$^+$ ions trapped, embedded into and sympathetically cooled via
Coulomb interactions by co-trapped $^{40}$Ca$^+$ ions. Furthermore, we discuss
different options for a non-destructive identification of the sympathetically
cooled thorium ions in the trap, and describe in detail our chosen experimental
method, identifying mass and charge of thorium ions from the positions of
calcium ions, as their fluorescence is imaged on a CCD camera. These findings
are verified by means of a time-of-flight signal when extracting ions of
different mass-to-charge ratio from the Paul trap and steering them into a
detector.
