Speaker
Description
The origin and character of the fission fragment angular momenta are currently topics of intense theoretical study. We describe how the angular-momentum bearing modes of the evolving dinuclear complex are being agitated at different rates by multiple transfers of individual nucleons, the mechanism long understood to be the primary cause of the transport phenomena displayed by damped nuclear reactions, including the generation of the angular momenta of the fragments [1,2]. The resulting fragment angular momenta are predominantly perpendicular to the fission axis and, although they are built up from collective rotational modes in which the two spins are highly correlated, they nevertheless emerge as largely independent [3,4], a feature supported by recent experimental data [5].
The fission simulation code FREYA [6], which treats angular momentum as suggested by the nucleon-exchange mechanism, presents a powerful tool for exploring observational consequences of the correlated fragment spin distributions and a number of examples will be discussed. For example, there is a marked correlation between the fragment spin magnitudes and the photon multiplicity [4].
[1] J. Randrup, Transport of angular momentum in damped nuclear reactions, Nucl. Phys. A 383, 468 (1982).
[2] T. Dossing and J. Randrup, Dynamical evolution of angular momentum in damped nuclear reactions: (I) Accumulation of angular momentum by nucleon transfer, Nucl. Phys. A 433, 215 (1985).
[3] J. Randrup and R. Vogt, Generation of fragment angular momentum in fission, Phys. Rev. Lett. 127, 062502 (2021).
[4] R. Vogt and J. Randrup, Angular momentum effects in fission, Phys. Rev. C 103, 014610 (2021).
[5] J. Wilson et al., Angular momentum generation in nuclear fission, Nature 590, 566 (2021).
[6] J.M. Verbeke, J. Randrup, and R. Vogt, Fission Reaction Event Yield Algorithm FREYA 2.0.2, Comp. Phys. Comm. 222, 263 (2018).