  Neutron star mergers offer unique conditions for the creation of the heavy
elements and additionally provide a testbed for our understanding of this
synthesis known as the $r$-process. We have performed dynamical nucleosynthesis
calculations and identified a single isotope, $^{254}$Cf, which has a
particularly high impact on the brightness of electromagnetic transients
associated with mergers on the order of 15 to 250 days. This is due to the
anomalously long half-life of this isotope and the efficiency of fission
thermalization compared to other nuclear channels. We estimate the fission
fragment yield of this nucleus and outline the astrophysical conditions under
which $^{254}$Cf has the greatest impact to the light curve. Future
observations in the middle-IR which are bright during this regime could
indicate the production of actinide nucleosynthesis.
