Californium-254 and Kilonova Light Curves

Light Curve Observation and Simulation from GW170817 Kilonova Series

The collaboration led by FIRE(Fission in R-process Elements) members from LANL(Los Almos National Lab)/NC State/Notre Dame has explored several issues concerning the nuclear physics of Cf-254 production in NSM’s observation for the first time. They model r-process nucleosynthesis using PRISM(Version 2.0, by LANL/Notre Dame) with all relevant nuclear reaction channels and reheating of the ejecta handled self-consistently. Fission from neutron-induced, β-delayed and spontaneous(SF) channels are also included.

Fig.1 Upper panel: primary fission fragment yield of Cf-254(SF) calculated in the hybrid approach (see text). Bottom panel: the two-dimensional fragment yield of Cf-254(SF), with our charge distribution systematics. Stable nuclei are shaded black with the extent of FRDM2012 outlined in light gray.
The fission fragment yields of Cf-254 are constructed with a hybrid method that combines both theoretical and experimental data, see Figure.1. Due to the anomalously long half-life of this isotope and the efficiency of fission thermalization compared to other nuclear channels, it is identified that this single isotope, Cf-254, which has a particularly high impact on the brightness of electromagnetic transients associated with mergers on the order of 15 to 250 days, see Figure 2.

The production of Cf-254 implies the nucleosynthesis of at least some actinide material. Thus, a combined approach of improving experimental knowledge in this region along with the coupling of late-time light curves with nucleosynthetic simulations have the potential to play a major role in cementing the origin of the heaviest r-process elements. This work has been accepted for publication by APJL.

Further Reading: arXiv:1806.09724

Fig 2 Effective heating rates, including energy partitioning between decay products and their thermalization, with and without contribution from spontaneous fission of actinides, in particular Cf-254. The dark purple solid line shows the (thermalized) contribution from fissioning Cf-254 nuclide alone.

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