  Cerium-134 is an isotope desired for applications as a chemical analogue to
the promising therapeutic radionuclide $^{225}$Ac, for use in bio-distribution
assays as an in vivo generator of the short-lived positron-emitting isotope
$^{134}$La. In the 50-100 MeV energy range relevant to the production of
$^{134}$Ce by means of high-energy proton bombardment of lanthanum, existing
cross section data are discrepant and have gaps at important energies. To
address these deficiencies, a series of 17 $^{139}$La foils (99.919% natural
abundance) were irradiated in two stacked-target experiments: one at the LANL's
Isotope Production Facility with an incident proton energy of 100 MeV, and a
second at BNL's Brookhaven Linac Isotope Producer with an incident proton
energy of 200 MeV - a complete energy range spanning approximately 55-200 MeV.
Cross sections are reported for 30 products of $^{139}$La(p,x) reactions
(representing up to 55% of the total non-elastic cross section), in addition to
24 residual products measured in the $^{nat}$Cu and $^{nat}$Ti foils that were
used as proton flux monitors. The measured production cross sections for
$^{139}$La reactions were compared to literature data as well as default
calculations from the nuclear reaction modeling codes TALYS, EMPIRE and ALICE,
as well as the TENDL-2023 library. The default calculations typically exhibited
poor predictive capability, due to the complexity of multiple interacting
physics models in this energy range, and deficiencies in preequilibrium
reaction modeling. Building upon previous efforts to evaluate proton-induced
reactions in this energy range, a parameter adjustment procedure was performed
upon the optical model and the two-component exciton model using the TALYS-2.0
code. This resulted in an improvement in $^{139}$La(p,x) cross sections for
applications including isotope production, over default predictions.
