Generation and Evolution of Fission Fragment Angular Momenta: A Global and Microscopic Study

How the fission fragment angular momenta (FFAM) develop dynamically from nothing is a crucial issue in the study of fission mechanism. To this end, we construct a time-dependent generator coordinate method that includes multiple rotations of fragments and their relative motion, the coupling between rotations, as well as vibrations based on the covariant density functional theory. We investigate the generation of FFAM from the equilibrium state of the compound nucleus to a large separation of fission fragments for the first time. Remarkably, the probability distribution of FFAM exhibits a rapid fluctuation in the two-dimensional FFAM plane during the forming process of fragments and takes shape as the fragments are basically formed. The final distributions of FFAM are consistent with the experimental measurements and the sawtooth-like mass dependence of average FFAM is reproduced very well. We also find that the magnitudes of FFAM are almost uncorrelated for lower and medium angular momenta, while strong correlations of orientations at the opening angle $\phi_{\rm LH}\approx 26^{\rm o}$, $100^{\rm o}$, and $160^{\rm o}$ are predicted due to the quantum fluctuations