| Abstract : | Short-lived radioisotopes 129I and 247Cm are almost exclusively produced by the rapid neutron capture process (r-process) and were present in the early Solar system (ESS) as confirmed by meteoritic data. A recent study by Cote et al. (2021) has claimed that the observed abundances 129I and 247Cm in the ESS are from one single “last” r-process event due to the very low frequency of r-process sources. This, when combined with the fact that 129I and 247Cm have identical lifetimes of ~15.6 Myr, can be used to directly constrain the nature of the last r-process event. The conclusion by Cote et al. (2021) was based on a one-zone Galactic chemical evolution code that modelled the temporal stochasticity of r-process events in the Solar neighbourhood. Here, we use the turbulent gas diffusion formalism that can simulate both the temporal and spatial stochasticity associated with rare r-process sources. We find that 129I and 247Cm in the ESS do not come entirely from a single major event but get contributions from at least two more minor contributors. This has a dramatic effect on the evolution of the 129I/247Cm ratio when 2-3 different r-process sources, that are equally frequent but have distinct 129I/247Cm production ratios, are considered. In this case, the measured ESS value in meteorites does not necessarily correspond to that of the “last” major r-process event and consequently, cannot be used to constrain it. Interestingly, however, we find that the requirement of concordance of the observed 129I/127I and 247Cm/235U ratio in the ESS is a crucial constraint. We find that important constraints on the properties of r-process sources that were operating during the formation of the Solar system can still be made using the observed value of 129I/247Cm ratio in the ESS. |
